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UBC Theses and Dissertations

The input stage of a TV-computer reading system for the blind Tsang, Robert Chuen Bong 1973

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THE INPUT STAGE OF A TV-COMPUTER READING SYSTEM FOR THE BLIND by ROBERT CHUEN BONG TSANG B.ENG.,McGill University,1 9 7 1 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n the department of E l e c t r i c a l Engineering We accept t h i s t h e s i s as conforming to the required standard Research Supervisor Members of the committee Actin g Head of the Department THE UNIVERSITY OF BRITISH COLUMBIA Ju l y , 1973 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h C olumbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada ABSTRACT The input stage of a TV-computer reading system has been b u i l t using s t a t e - o f - t h e - a r t integrated c i r c u i t s . A' stroboscopic sampling method i s used. Programs are developed to rearrange the input data f o r l a t e r proce-ssing. The system i s also a v a i l a b l e to work as an image enlarger f o r people with low-vision. Judging from the appearance of the f i n a l d i s p l a y s , the si g n a l - t o - n o i s e r a t i o i s acceptable. The p o s s i b i l i t y of inc o r p o r a t i n g an automatic focus device i s examined and an algorithm i s developed to t h i s end. Best focus i s obtained by ad j u s t i n g the camera's lens to maximize the *T* f u n c t i o n which i s r e l a t e d to the d i f f e r e n c e s i n the greyness between samples. The hardware and software are developed f o r the TV camera to work with a PDP-12 computer as an input system. Sugges-tio n s f o r f u r t h e r improvements of the system are a l s o included. i i TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i i i LIST OF SYMBOLS V LIST OF ILLUSTRATIONS v i ACKNOWLODGEMENT . ; i x 1. INTRODUCTION 1 1.1 DIRECT-TRANSLATION MACHINES EVALUATIONS . . . . 1 1.2 A RELATIVELY COMPLEX READING SYSTEM 3 1.3 INPUT CONSIDERATIONS OF READING SYSTEMS . . . . 6 1.4 THESIS ORGANIZATIONS . . . 7 2. •STROBOSCOPIC-SAMPLING* TECHNIQUE . 9 3. A TV-COMPUTER INPUT AND DISPLAY SYSTEMS DESCRIPTION AND DESIGN CRITERIA 13 4. HARDWARE IMPLEMENTATION AND PERFORMANCE 19 4.1 PHASE-LOCKED LOOP (PLL) 19 4.1.1 HISTORY AND DEVELOPMENT 19 4.1.2 PHASE-LOCKED LOOP THEORY OF OPERATION . . 20 4.1.2.a THE BASIC LOOP 20 . 4.1.2.D THE LOOP FILTER 22 4.1.3 PLL APPLICATIONS 26 4.2 THE FREQUENCY COUNTER , . 32 4.3 THE SAMPLE-AND-HOLD UNIT 34 4.4 AUXILIARY DISPLAY CIRCUITRY . . . . . . . . . . 36 4.5 SAMPLING PULSE CONTROL CIRCUIT FOR HIGH RESOLUTION PICTURES 39 5. PROGRAMMING TECHNIQUES • ^3 i i i 5.1 INPUT1 ^3 5.2 OUTl kk 5.3 MAN2 46 5.4 D I P I . . ^9 5.5 INTERl 51 5.6 HP3 51 5.7 INTER2 51 5.8 HP4 51 6. READING ASSIST DEVICES FOR PEOPLE WITH LOW VISION . . 55 7. FOCUS CONSIDERATIONS 58 7.1 PROPERTIES OF FOCUS 58 7.2 A PROPOSED METHOD FOR THE PRESENT SYSTEM (THE T FUNCTION) 60 7.2.a SOFTWARE IMPLEMENTATION OF T FUNCTION . . . 62 7.2.b EXPERIMENTAL RESULTS ON THE T FUNCTION . . . 62 8. CONCLUSIONS 66 BIBLIOGRAPHY 69 APPENDIX 1 : TECHNICAL INGORMATION ON THE CAMERA 72 APPENDIX 2 : COMPUTER SYSTEM DESCRIPTION 73 i v L I S T O F S Y M B O L S M T h e f r e q u e n c y m u l t i p l i c a t i o n s . D T h e f r e q u e n c y c o u n t d o w n . f s T h e s a m p l i n g f r e q u e n c y . f o T h e m a x i m u m s i g n a l s s a m p l i n g f r e q u e n c y . N f T h e n u m b e r o f f r a m e s t o s a m p l e o n e c j o m p l e t j e p i c t u r e . 61 T h e p h a s e o f t h e i n p u t s i g n a l . Qo T h e p h a s e o f t h e V C O o u t p u t * v d T h e p h a s e d e t e c t o r v o l t a g e o u t p u t . F ( s ) T h e l o o p f i l t e r t r a n s f e r f u n c t i o n . K d T h e - p h a s e d e t e c t o r g a i n f a c t o r . ( v o l t s / r a d i a n s ) K o T h e V C O g a i n c o n s t a n t . ( r a d i a n s / s e c o n d s / v o l t s ) ™iS s ) T h e L a p l a c e t r a n s f o r m o f t h e l o o p t r a n s f e r f u n c t i o n w i t h p a s s i v e l o o p f i l t e r . H 2 ( s ) T h e L a p l a c e t r a n s f o r m o f t h e l o o p t r a n s f e r f u n c t i o n w i t h a c t i v e l o o p f i l t e r . w n T h e " n a t u r a l f r e q u e n c y " o f t h e l o o p . S T h e " d a m p i n g f a c t o r " o f t h e l o o p . K K o d T h e " l o o p g a i n " . ( t i m e ) - 1 f A r e f e r e n c e t h r e s h o l d f o r t h e f u n c t i o n F . O D ± T h e g r e y n e s s a t a p o i n t . ( o p t i c a l d e n s i t y ) n T h e n u m b e r o f p o i n t s i n t h e i m a g e w i t h 0 D i >» ^ • V e 2 T h e v i d e o s a m p l e s v o l t a g e s . F T h e f u n c t i o n F . T T h e T f u n c t i o n . A e i T h e d i f f e r e n c e i n g r e y n e s s b e t w e e n a n y t w o p o i n t s . P L L P h a s e - l o c k e d l o o p . V C O V o l t a g e - c o n t r o l l e d o s c i l l a t o r . LIST OF ILLUSTRATIONS Figure NO. Page (1) Reading machine system diagram . . . . . . . . . h (2) Schematic diagram of a t y p i c a l cable TV system . 5 (3) A TV-computer reading system with synthetic speech output • « 8 (k) An i l l u s t r a t i o n of stroboscopic scanning . . . . 10 (5) The corresponding p o s i t i o n of s t r o b o s c o p i c a l l y sampled points i n the p i c t u r e • • • • 11 (6) S t r o b o s c o p i c a l l y sampled s i g n a l . . . . . . . . 11 (7a) P i c t u r e d i s p l a y f o r p i c t u r e without s t a r t - o f -p i c t u r e pulse . . . . . . . . . . . . . . . . . 12 (7b) P i c t u r e d i s p l a y f o r p i c t u r e with s t a r t - o f -p i c t u r e pulse 12 (8) Block diagram f o r the TV-computer input system . 17 (9) TV sampling u n i t with a u x i l i a r y d i s p l a y u n i t (Block diagram) . . . . . . . . . . . 18 (10) Basic loop block diagram . . . . . . * • • . • • 20 ( l l a ) Passive f i l t e r 23 ( l i b ) A c t ive f i l t e r 23 (12) Frequency response; high-gain, second-order loop . . . . . . . . . . . . . . • • • . . . • * 25 (13) E r r o r response of high-gain loop 25 (14) PLL frequency m u l t i p l i c a t i o n block diagram . . . 27 (15) The a c t u a l loop f i l t e r used 27 (16) PLL (NE562) frequency m u l t i p l i c a t i o n c i r c u i t diagram . . . . . 29 v i (17) The PLL frequency multiplication stages * . . • • 30 (18) F i r s t stage PLL output and 31.5 kc signal from camera. (20 usec/div., l v / d i v . ) . 30 (19) Second stage PLL output waveform and 31•5 kc signal from camera. (10 usec/div., lv/div.) . . . 31 (20) Third stage PLL output waveform and 31.5 kc signal from camera. (5 usec/div., lV/div.). . . • 31 (21) The counter c i r c u i t u t i l i z i n g a d i g i t a l comparator • • • • 33 (22) Schematic of a sample and hold unit . . . . . . . 35 (23) Sample and hold timing diagram 35 (24) The auxiliary display system . . . . . . . . . . 36 (25) The v e r t i c a l sawtooth generator . . . . . . . . . 37 (26) The horizontal sawtooth generator . . . . . . . . 37 (27) Examples of stroboscopically sampled picture display on oscilloscope . * • . . . . • » » • • • 38 (28) The multivibrator delay c i r c u i t s 4 l (29) Sampling pulse control c i r c u i t with computer controls 4-2 (30) Flow diagram for INPUT1 . . . . . . . 45 (31) The CRT grid 46 (32) Flow diagram for 0UT1 47 (33) Cont'ed flow diagram for OUTl 48 (34) Flow diagram of MAN2 50 (35) Picture display for DIP1 • 53 (36) Picture display for INTER1 and HP3 . . . . . . . 54 (37) Example of a contour display 54 v i i (38) I l l u s t r a t i o n o f r e a r r a n g e d p r i n t l i n e d i s p l a y • . 5*> (38a) P o s i t i v e d i s p l a y e x a m p l e o f r e a r r a n g e d p r i n t l i n e 57 (38b) N e g a t i v e d i s p l a y e x a m p l e o f r e a r r a n g e d p r i n t l i n e . . . . . . 57 (39) G r e y n e s s p r o f i l e v e r s u s f o c u s c u r v e • • • • • • • 6 l (40) T w o s a m p l e s o f t h e v i d e o s i g n a l . . . . . . . . . 6 l (kl) F l o w d i a g r a m f o r c o m p u t i n g t h e T f u n c t i o n . . . . 6k (k2) T h e ' T ' c u r v e f o r p r i n t e d p a g e . . . . . . . . . 65 (k3) T h e * T ' c u r v e f o r t h e l e t t e r «b« . . . . . . . . 65 {kk) L I N C m o d e m e m o r y o r g a n i z a t i o n . . . . . . . . . . 7 4 (4-5) P D P m o d e m e m o r y o r g a n i z a t i o n • • • • • • • • » • 7k v i i i ACKNOWLEDGEMENT The author wishes to thank Dr. M.P.Beddoes f o r h i s u s e f u l suggestions and the various i n d i v i d u a l s f o r t h e i r help i n the p r o j e c t . He-would also l i k e to thank Dr. F. Bowers f o r reading the t h e s i s . He a l s o wishes to express h i s gratitude to the National Research Counci l of Canada f o r the f i n a n c i a l support throughout the p r o j e c t . He would also l i k e to thank Miss Eugenia Chan f o r her help i n typing the manuscript. i x 1 1 . I N T R O D U C T I O N T h i s t h e s i s i s a n i n s t r u m e n t a t i o n t h e s i s . A s t r o b o s c o p i c - s a m p l e r h a s b e e n b u i l t w h i c h s a m p l e s t h e o u t p u t o f a n o r m a l t e l e v i s i o n c a m e r a ( S o n y 2 0 0 0 ) s u f f i c i -e n t l y s l o w l y t o b e i n g e s t e d b y a d i g i t a l c o m p u t e r o r b y a d i g i t a l p r o c e s s o r . F o u r r e a s o n s c a n b e g i v e n f o r d o i n g t h e . -w o r k : a ) . T h e s a m p l e r c a n b e u s e d t o i n t e r f a c e t h e c a m e r a a n d a c o m p u t e r i n a s p e l l e d s p e e c h r e a d i n g m a c h i n e f o r t h e b l i n d . b ) . A t t h e t i m e o f s t a r t i n g t h i s w o r k , n o o t h e r s a m p l e r w a s a v a i l a b l e , a n d t h i s w o r k g i v e s o r d e r o f m a g n i t u d e e s t i m a t e s o f c o s t a n d t h e p e r f o r m -a n c e o f s u c h a s a m p l e r . c ) . T h e s a m p l e r c a n b e u s e d i n a p r o p o s e d r e a d i n g a i d f o r p e o p l e w i t h l o w v i s i o n i n w h i c h m a g n i f -i c a t i o n a n d r e a r r a n g e m e n t o f t h e p r i n t m a t e r i a l i s r e q u i r e d . d ) . A m e t h o d f o r a u t o m a t i c f o c u s i n g t h e t e l e v i s i o n c a m e r a c a n b e e x p l o r e d . 1 . 1 D I R E C T - T R A N S L A T I O N M A C H I N E S E V A L U A T I O N S ; I n t h e p a s t d e c a d e , m u c h e f f o r t h a s b e e n s p e n t i n b u i l d i n g d i r e c t - t r a n s l a t i o n m a c h i n e s f o r t h e b l i n d . D i r -e c t - t r a n s l a t i o n m a c h i n e s a r e t h o s e d e v i c e s t h a t c o u l d t r a n -s f o r m d i r e c t l y o p t i c a l i m a g e s f r o m a p r i n t p a g e i n t o a u d i t o r y o r t a c t i l e d i s p l a y s ^ ^ . S o m e o f t h e m o r e s u c c e s s f u l o n e s a r e t h e O p t a e o n , t h e O p t o p h o n e , t h e L e x i p h o n e , t h e V i s o t o n e r a n d t h e V i s o t a c t o r e t c . w h i c h p r o v i d e e i t h e r a u r a l o r t a c t i l e o u t p u t s w h i c h t h e b l i n d p e r s o n i s c a p a b l e o f s e n s i n g . T h e O p t a c o n r e a d e r t r a n s l a t e s a n a r e a o f a p a g e c o r r e s p o n d i n g t o t h e s i z e o f a l e t t e r i n t o a t a c t i l e i m a g e . T h e u s e r m a n u a l l y s c a n s t h e p a g e w i t h o n e h a n d w h i l e r e c e i v i n g t h e t a c t i l e o u t -p u t w i t h t h e o t h e r h a n d . T h e V i s o t o n e r g i v e s a u d i t o r y o u t p u t s c o m p o s e d o f s e q u e n c e s o f c h o r d s s i m i l a r t o t h o s e p r o d u c e d b y t h e O p t o p h o n e . T h e V i s o t a c t o r h a s t h e s a m e i n p u t s y s t e m a s t h e V i s o t o n e r , b u t g i v e s a t a c t i l e o u t p u t . T h e L e x i p h o n e u s e s 54 p h o t o c e l l s a r r a n g e d i n a o n e - d i m e n s i o n a l a r r a y a s i n p u t e l e m e n t s a n d w i t h t h e p r o v i d e d a l i g n m e n t a d j u s t m e n t s , t h e u s e r s c a n s t h e p r i n t e d m a t e r i a l m a n u a l l y a n d a n a u d i t o r y o u t p u t i s g e n e r a t e d b y a s p e c i a l l y m o d u l a t e d s q u a r e w a v e g e n e r a t o r . S u c h a n o u t p u t h a s to b e l e a r n e d b y t h e r e a d e r b e f o r e t h e m a c h i n e i s u s a b l e . A l l t h e a f o r e m e n t i o n e d d i r e c t -t r a n s l a t i o n m a c h i n e s a r e s i m p l e a n d i n e x p e n s i v e b u t d e m a n d m o t i v a t i o n a n d t r a i n i n g f o r e f f e c t i v e u s e . T h e s e m a c h i n e s ^ 1 ^ p r o v i d e r e a d i n g s p e e d s o f u p t o 60 w o r d s p e r m i n u t e ( W P M ) f o r t h e a v e r a g e b l i n d s u b j e c t s . S u c h f i g u r e s s h o w t h a t t h e e f f i c i e n c y o f t h e s e m a c h i n e s i s s t i l l l o w c o m p a r e d t o t h e h u m a n a u d i t o r y i n f o r m a t i o n p r o c e s s i n g c a p a b i l i t i e s . N o r m a l s p e e c h c a n b e u n d e r s t o o d a t r a t e s e x c e e d i n g 200 W P M . ^ ^ T h i s i n d i c a t e s t h a t t h e a u d i t o r y c h a n n e l i s c a p a b l e o f p r o c e s s i n g c o m p l e x s i g n a l s a t h i g h r a t e s . T h e d i r e c t - t r a n s l a t i o n m a c h -i n e o u t p u t , i t s e e m s , f a l l f a r f r o m t h i s o p t i m u m i n f o r m a t i o n r a t e s . In a d d i t i o n to the r e l a t i v e l y low output rate of most d i r e c t t r a n s l a t i o n machines, the various mechanical adjustments (e.g. focusing, alignments, etc.) necessary i n these machines f u r t h e r complicates the operations of the machine. 1*2 A RELATIVELY COMPLEX READING SYSTEM; The above considerations suggest that a r e l a t i v e -l y complex reading system i s needed, P i g . ( l ) . Such a machine includes a mini-to medium-size d i g i t a l computer as a proces-si n g and c o n t r o l u n i t of the reading system. I t w i l l t a l k to the reader using s p e l l e d speech code. I t w i l l scan a whole page without mechanical scanning. I t processes the incoming s i g n a l s , extracts s a l i e n t features of alphabet characters, and recognizes the l e t t e r using the s a l i e n t features. For the output stage of the system, s p e l l e d speech output i s cur-r e n t l y a v a i l a b l e under computer c o n t r o l . Also included i n F i g . ( l ) are the p e r i p h e r a l d i s p l a y monitor and t e l e t y p e w r i t e r used i n the present work. (2) A recent r e p o r t v ' has i n d i c a t e d that before the end of the decade, 40 to 60 $ of a l l households w i l l probably have cable connections to i n s t a l l a t i o n s with a c e n t r a l i z e d head-end, F i g . ( 2 ) , to provide services such as h e a l t h serv-i c e s , consumer education, formal i n s t r u c t i o n , and community development etc. I t appears that the i n c l u s i o n of a computer u n i t as an information processor i s a p r a c t i c a l p r o p o s i t i o n . The system of F i g . ( l ) i s part of ongoing research i n t o f u t -ure reading machines. Further examples where computers are CARRIAGE CONTROL PAGE . SCANNER i ; • ,i 1 SCANNER CONTROL DISPLAY p < DATA LINK SPELLED SPEECH GENERATOR < PDP-12 COMPUTER TYPEWRITER Fit?, ( l ) : Reading machine system diagram 5 F i g . ( 2 ) ; Schematic diagram o f a t y p i c a l c a b l e  T Y system. u s e d a r e t h e A u d i o - R e s p o n s e - T i m e - S h a r e d ( A R T S ) S e r v i c e B u r -e a u d e v e l o p e d b y T h e A m e r i c a n S y s t e m I n c . i n W a t e r t o w n , M a s -s a c h u s e t t e s , a n d t h e S p e l l e x S y s t e m d e v e l o p e d b y D r . B e d d o e s a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a . T h e l a t t e r s y s t e m e n a b l e s b l i n d p e o p l e t o t y p e l e t t r e r - p e r f e c t c o r r e s p o n d e n c e , p r o o f r e a d m a n u s c r i p t s , c a l c u l a t e b o o k k e e p i n g p r o b l e m s , a n d w r i t e c o m p u t e r p r o g r a m s . U n l i k e ' d i r e c t - t r a n s l a t i o n 1 u n i t s w h i c h a r e d e s i g n e d f o r l o w c o s t a n d s i m p l i c i t y , a p a g e r e a d i n g s y s t e m i s e x p e n s i v e . H o w e v e r , w i t h t h e r e c e n t d e v e l o p m e n t o f M S I & L S I t e c h n o l o g y , t h e c o s t s a r e d e c r e a s i n g . I f t h e s y s t e m c o u l d b e r u n o n a t i m e s h a r e d b a s i s w i t h m u l t i p l e r e m o t e u s e r t e r m i n a l s , t h e c o s t p e r i n s t a l l a t i o n c a n b e e c o n o m i c a l ^ T h e r e f o r e , a c e n t r a l i z e d c o m p u t e r c o n t r o l r e a d i n g s y s t e m s e e m s t o b e a t r e n d f o r f u t u r e r e a d i n g a i d d e v e l o p m e n t s . 1.3 I N P U T C O N S I D E R A T I O N S O F R E A D I N G S Y S T E M S ; I n d e s i g n i n g s u c h a c o m p u t e r c o n t r o l l e d r e a d i n g s y s t e m , t h e f i r s t t h i n g t h a t o n e h a s t o c o n s i d e r i s t h e k i n d o f i n p u t d e v i c e s t o b e u s e d . M a n u a l p h o t o c e l l s c a n n i n g a s u s e d i n m o s t o f t o d a y s d i r e c t - t r a n s l a t i o n u n i t s i s n o t s u i t -a b l e , i n s t e a d , a n e l e c t r o n i c s c a n n i n g i n p u t d e v i c e i s n e c e s -s a r y t o o b t a i n t h e n e c e s s a r y h i g h i n p u t r a t e . S u c h a d e v i c e s h o u l d b e a b l e t o s c a n a p a g e o f i n f o r m a t i o n a n d r e q u i r e o n l y m i n i m a l a m o u n t o f h a r d w a r e f o r i n t e r f a c i n g w i t h t h e c o m p u t e r . O n c e t h e i n f o r m a t i o n h a s b e e n s t o r e d , t h e n e c e s s -a r y p r o g r a m s c a n b e d e v e l o p e d t o p r o v i d e t h e r e q u i r e d s e r v -7 (5)* U n t i l r e c e n t l y v / t n o c o m m e r c i a l v i d e o d i g i t a l c o m p r e s s o r h a s b e e n a v a i l a b l e . A n i n t e r f a c e h a s b e e n b u i l t t o d e m o n s t r a t e a c c e p t a b l e s i g n a l - t o - n o i s e r a t i o f o r v i s u a l d a t a d i s p l a y s f o r u s e b y p e o p l e w i t h l o w v i s i o n , ( i . e . i m a g e e n l a r g e r ) . T h e i n t e r f a c e i s s u i t a b l e a s a f r o n t e n d t o c a b l e T V f o r r e a d i n g m a c h i n e s . T h e i n t e r f a c e i s a n e x e r c i s e i n d i g i t a l c i r c u i t d e s i g n . P r e l i m i n a r y e x p e r i m e n t s w i t h t h e i n t e r f a c e a r e r e p o r t e d . 1.4 T H i f i S I S ORGANIZATION; T h e t h e s i s d e a l s a l m o s t e n t i r e l y w i t h t h e d e s i g n a n d t h e u s e o f t h e T V - c o m p u t e r i n t e r f a c e u s e d t o • m a t c h 1 t h e T V c a m e r a t o t h e r e s t o f t h e r e a d i n g s y s t e m i l l u s t r a t e d i n b l o c k f o r m i n F i g . ( 3 ) . I n s e c t i o n 2, s c a n n i n g m e t h o d s i n t h e • c a m e r a - a n d s a m p l i n g - t e c h n i q u e s u s e d - i n t h e . i n t e r f a c e " . a r e d i s -c u s s e d i n g e n e r a l t e r m s . T h e s p e c i f i c f o r m o f t h e i n t e r f a c e i s g i v e n i n s e c t i o n 3. D e t a i l s o f h a r d w a r e i m p l e m e n t a t i o n a r e g i v e n i n s e c t i o n 4. H i g h l i g h t s o f c o m p l e m e n t a r y p r o g r a m s a r e g i v e n i n s e c t i o n 5, a n d t h e s e i n c l u d e s e x p e r i m e n t a l r e s u l t s f r o m s c a n n i n g t e x t a n d b l a c k - w h i t e l e t t e r s . T h e a p p l i c a t i o n o f t h e s y s t e m a s a n i m a g e e n l a r g e r f o r r e a r r a n g e d p r i n t l i n e i s d i s c u s s e d i n s e c t i o n 6. S e c t i o n 7 d e a l s w i t h c o n s i d e r a t i o n s f o r i m p l e m e n t i n g a u t o m a t i c f o c u s . * A v i d e o c o m p r e s s o r i s m a d e a v a i l a b l e b y C o l o r a d o V i d e o , I n c . i n B o u l d e r , C o l o r a d o , U . S . A . ( J a n . , 1 9 7 3 ) . 8 TV CAMERA TV-COMPUTER INTERFACE PDP-12 COMPUTER •= = = = === = SCANNER CONTROL A/D CONVERTER FEATURE EXTRACTOR RECOGNIZER OUTPUT CONTROL D/A CONVERTER SYNTHETIC SPEECH DISPLAY UNIT F i g , ( 3 ) : A TV-computer reading system with synthetic  speech output. 2. • S T R O B O S C O P I C - S A M P L I N G 1 T E C H N I Q U E I n t h e p r e s e n t s y s t e m a t e l e v i s i o n c a m e r a i s u s e d a s a n e l e c t r o - o p t i c a l s c a n n i n g u n i t . T h e c a m e r a u s e s s c a n n i n g w i t h o d d a n d e v e n f r a m e s i n t e r l a c e d . I t t a k e s 6k u s t o s c a n a h o r i z o n t a l l i n e . I t - t a k e s 2/60 (31*6 m s ) s e c o n d s t o s c a n t h e e n t i r e i m a g e o n c e . T h e s c a n n i n g c o n s i s t s o f 525 h o r i z o n t a l s c a n n i n g l i n e s , A s t r o b o s c o p i c s a m p l i n g t e c h n i q u e w h i c h a p p e a r s t o b e ' p s e u d o r a n d o m ' i s u s e d t o s a m p l e t h e v i d e o s i g n a l . S e v e r a l r e q u i r e m e n t s h a v e t o b e s a t i s f i e d b y t h e s a m p l i n g f r e q u e n c y . T h e s a m p l i n g f r e q u e n c y h a s t o b e a t a s p e e d s u c h t h a t t h e c o m p u t e r c a n r e s p o n d i n t h e r e s t r i c t e d t i m e i n t e r v a l b e t w e e n s a m p l e s . I t h a s t o h a v e a c o n s t a n t t i m e r e l a t i o n -s h i p w i t h t h e . r a s . t . e r s c a n n i n g d u r i n g t h e e n t i r e s a m p l i n g p r o c e s s t o a v o i d p i c t u r e d i s t o r t i o n . T h e n u m b e r o f p o i n t s b e t w e e n t w o c o n s e c u t i v e s a m p l e s c a n n o t c o n t a i n a c o m m o n f a c t o r w i t h t h e t o t a l n u m b e r o f p o i n t s t o a v o i d r e p e t i t i v e s a m p l i n g . F i g . ( k ) g i v e s a n e x a m p l e o f a n a l l o w a b l e s a m p l i n g p r o c e s s w i t h f o u r p o i n t s b e t w e e n s a m p l e s . N o t e t h a t f o u r i s p r i m e w i t h n i n e w h i c h i s t h e t o t a l n u m b e r o f p o i n t s i n t h i s c a s e . C o n s e q u e n t l y , n o r e p e t i t i v e s a m p l i n g w o u l d o c c u r . T h e s t r o b o s c o p i c s a m p l e p u l s e s a r e g e n e r a t e d f r o m t h e m a s t e r o s c i l l a t o r i n t h e c a m e r a . T h e m a s t e r o s c i l l -a t o r f r e q u e n c y i s 31.5 k c w h i c h i s t w i c e t h e l i n e s c a n n i n g f r e q u e n c y . T h i s f r e q u e n c y i s m u l t i p l i e d u p M t i m e s t o g i v e a d e s i r e d f r e q u e n c y c o r r e s p o n d i n g t o a r e q u i r e d p i c t u r e r e s o -l u t i o n . T h e n i t i s d i v i d e d d o w n D t i m e s b y a f r e q u e n c y d i v i d e r 10 to give the stroboscopic pulses at a frequency f which can be expressed by: f ° 3 1 . 5 (M/D) kc where: f i s the sampling frequency, s M i s the frequency multiplication. D i s the frequency countdown which i s prime with the to t a l number of picture points. e.g. A 128*525 points picture can be ingested by the computer using M=»128, D=319» The stroboscopic sampling frequency f = 6»3 kc and the equivalent s picture sampling frequency f i s (128*15*75) kc " .2 .MHz.. The number of .frames for one complete picture i s N F - 2(f Q/f s ) « 6 3 5 , and the time req-uired • N^(l/6o) seconds or 10.6 seconds, where: f Q i s the s i g n a l s sampling frequency. N F i s the number of frames to sample one complete picture. ® 1 2 3 $ @ k 5 6 ® 7 8 9 1,2,3,4 picture point positions. ®»^®»®» sampling order, Fig.(4): An i l l u s t r a t i o n of stroboscopic scanning. 11 odd frame 12 F i g . ( 7 b ) ; P i c t u r e d i s p l a y f o r p i c t u r e with s t a r t - o f - p i c t u r e pulse. 13 3. A TV-COMPUTER INPUT AND DISPLAY SYSTEM DESCRIPTION  AND DESIGN CRITERIA; In t h i s section, the camera-computer i n t e r f a c e and the a u x i l i a r y d i s p l a y s u n i t s are described. In the design, f l e x i b i l i t y of the i n t e r f a c e has been s a c r i f i c e d i n order to keep the hardware simple. Bearing i n mind that a b l i n d person w i l l be using the i n t e r f a c e , the number of adjustments needed has been kept to a minimum. The i n t e r f a c e operates with a • no rmal 1 camera. A block diagram i s shown i n F i g . ( 8 ) . The sample pulses are generated from the master o s c i l l a t o r i n the camera, and the proper time r e l a t i o n s h i p i s maintained to give a phase-locked output. A phase-locked loop (PLL) i s used to maintain the necessary phase l o c k i n g . The phase-locked loop also provides the frequency m u l t i p l i c a t i o n (described i n the hardware s e c t i o n 4.1) needed to achieve the required r e s o l u -t i o n . The video, the master o s c i l l a t o r output, the v e r t i c a l sync, and the h o r i z o n t a l sync s i g n a l s from the camera are used. The master o s c i l l a t o r output, 31.5 kc, i s fed i n t o the input of the frequency m u l t i p l i e r (PLL) to give a high frequency output. The m u l t i p l i c a t i o n w i l l represent the number of points per l i n e i n the r e s u l t i n g d i g i t a l p i c t -ure. The output of the m u l t i p l i e r i s fed to a frequency d i v i -der which provides the necessary countdown to generate the stroboscopic sampling pulses. As mentioned e a r l i e r , t h i s countdown should contain no f a c t o r s that are common to the t o t a l number of points i n the d i g i t a l p i c t u r e . The next stage of the unit i s a sample-and-hold u n i t . The video from the camera i s fed int o the input of the sample-and-hold u n i t . The output from the frequency d i v i d e r provides the sampling pulses f o r the sample-and-hold u n i t . The requirements on the sample-and-hold unit-are that the sampling window should be narrow enough f o r the r e s o l u t i o n needed (e.g. sampling window $ 1 2 5 ns f o r 512 points per l i n e . ) and a long enough hold time ( i . e . n e g l i -g i b l e decay i n 50 ns). The video s i g n a l i s fed i n t o the a t t -enuator before i t i s fed to the sample-and-hold u n i t . This i s necessary since the sample-and-hold unit requires + 1 V peak to peak f o r proper operation. The sampled video i s then fed to an analog-to-d i g i t a l converter. M u l t i - b i t s are used for. each samples because the greyness information can be taken i n by the computer f o r l a t e r processing and research purposes. The a n a l o g - t o - d i g i t a l converter u n i t i s incorporated i n the P D P - 1 2 computer data terminal. I t provides a 10-bit d i g i t i -z a t i o n which i s more than ample since 10 b i t s correspond to 1024 grey l e v e l s . The sample pulses from the frequency count-er are stretched i n time and give the computer command to sample the sample-and-hold s i g n a l . Since the PDP-12 computer used has only 8k of core memory, an a u x i l i a r y memory un i t i s needed to store a l l the p i c t u r e information. A magnetic d i s c u n i t RK08 with 800,000 words capacity i s used. The incoming data i s f i r s t stored s e q u e n t i a l l y i n t o core memory and then t r a n s f e r r e d i n t o the d i s c i n block form, 2k or 4k at a time. Since the 15 d i s c unit works on a data break basis ( i . e . c y c l e s t e a l i n g b a s i s ) , the r e l a t i o n s h i p between the sampling frequency and the program execution time i s very c r i t i c a l . This w i l l be discussed i n s e c t i o n 5.1. Although the time r e l a t i o n s h i p between the camera, sampling pulses, and the computer has been maintained, there i s no guarantee that each time when the sampling process i s started, i t s t a r t s at the same p o s i t i o n i n the p i c t u r e . There-fore, a unit i s incorporated to permit the computer to s t a r t information storage when the TV scanning and the sampling process i s at the upper l e f t hand corner of the p i c t u r e . This can be achieved by putting the negatives of the v e r t i c a l sync, h o r i z o n t a l sync, and the sample pulses together i n t o a 3-input NOR gate. As a r e s u l t , the output of the NOR gate w i l l go high only i f a l l 3 inputs goes low at the same time. The computer has only to detect t h i s s t a r t - o f - p i c t u r e s i g n a l to commence s t o r i n g p i c t u r e information. With t h i s u n i t incorp-orated, i t can be sure that a complete p i c t u r e w i l l be stored instead of a fragmented one. Examples are given i n Pig.(7a) and (7b). An a u x i l i a r y d i s p l a y u n i t i s also constructed to monitor the sampled p i c t u r e using an o s c i l l o s c o p e . In such a case, instead of feeding to the computer, the sampled video i s used to z-modulate ( i n t e n s i t y modulation) the e l e c t -ron beam which i s scanning at a r a s t e r on the o s c i l l o s c o p e . The r a s t e r i s generated by two sawtooth generators ( i . e . v e r t i c a l and ho r i z o n t a l ) which are tr i g g e r e d by the v e r t i c a l and h o r i z o n t a l synchronization s i g n a l s from the TV camera. Consequently, the time r e l a t i o n s h i p between the d i s p l a y and the sampling process i s also maintained. A general block diagram of the system i s shown i n Fig.(8) & ( 9 ) . 31.5 kc PLL TV CAMERA MONITOR VIDEO SIGNAL NOR-GATS FREQUENCY DIVIDER SAMPLE PULSES S/H UNIT SAMPLED VIDEO lO-BTT A/D CONVERTER PDP-12 COMPUTER DISC UNIT RK08(S00,000 "WORDS) TO AUXILIARY UNIT PULSE STRETCHER VR12 CRT POINT DISPLAY Fig.(8): Block diagram f o r the TV-computer input system. H TV CAMERA HORIZONTAL SYNC PHASE-LOCKED LOOP VERTICAL SYNC SAWTOOTH GENERATOR (VERTICAL) SAWTOOTH GENERATOR (HORIZONTAL) FREQUENCY COUNTER VIDEO SIGNAL S/H INTENSITY MODULATION CRT DISPLAY Fiff, (9) i TV sampling unit with auxiliary display unit (Block diagram) H oo 19 4. HARDWARE IMPLEMENTATION AND PERFORMANCE The hardware u n i t f o r the TV-computer i n t e r f a c e can be divided i n t o several blocks. They are the phase-locked loop (the frequency m u l t i p l i e r ) , the frequency counter, the sample-and-hold u n i t , the a u x i l i a r y d i s p l a y c i r c u i t s , and the high r e s o l u t i o n sampling pulse c o n t r o l c i r c u i t s . Each of these blocks w i l l be described i n the fo l l o w i n g sections, 4.1 PHASE-LOCKED LOOP (PLL): The 31o5 kc s i g n a l from the camera master o s c i l -l a t o r i s fed int o a phase-locked loop to give a phase-locked output. The phase-locked loop a l s o provides a frequency mul-t i p l i c a t i o n . The highest frequency output gives the s p e c i f i c p i c t u r e r e s o l u t i o n . 4.1.1 HISTORY AND DEVELOPMENT: The basic concept of a phase-locked loop i s by no means new. I t has been known since the e a r l y 1 9 3 0's.^^ I t i s b a s i c a l l y an e l e c t r o n i c servo loop c o n s i s t i n g of a phase detector, a low pass f i l t e r , and a voltage c o n t r o l l e d o s c i l l a t o r . I t was used i n various instrumentations and space telemetry. I t was mainly constructed from d i s c r e t e components which made i t c o s t l y and complicated f o r system design. I t s use has thus been l i m i t e d to p r e c i s i o n measur-ments r e q u i r i n g very narrow bandwidths or a high degree of noise immunity. However, with the advent of recent develop-ments i n integrated c i r c u i t design and processing technology, the monolithic PLL has emerged to be a new and v e r s a t i l e 20 b u i l d i n g block i n the past two years, with i t s d i v e r s i t y i n a p p l i c a t i o n s s i m i l a r to the monolithic operational a m p l i f i e r . The monolithic PLL, due to i t s low cost and reduction i n complexity, has also opened up many new appl-i c a t i o n s which cost and complexity p r e v i o u s l y precluded. I t s a p p l i c a t i o n s include use as a very s e n s i t i v e f i l t e r , as a v a r i a b l e l o c a l o s c i l l a t o r , as a frequency synthesizer, as AM and FM demodulators, and as a tone decoder. 4.1_2 PHASE-LOCKED LOOP THEORY OF OPERATION: 4.1.2.a. THE BASIC LOOP: V d " Kd<<V *o> Phase detector 9 * F(s) -2-VCO Fig. (10 ): Basic loop block diagram The phase-locked loop fundamentally c o n s i s t s of a phase detector, a low pass f i l t e r and a voltage c o n t r o l l e d o s c i l l a t o r (VCO) F i g . ( l O ) . I t i s an e l e c t r o n i c servo loop. The input s i g n a l has a phase #^(t) and the VCO output has a phase &o(t). Assuming the phase i s locked and the phase det-ector i s l i n e a r , the output of the phase detector i s prop-o r t i o n a l to the d i f f e r e n c e i n phase between i t s inputs, namely, r = K (£ - o ) where: K. i s the 'phase-detector' gain f a c t o r (V/radian). 21 The output of the phase detector ( i . e . the phase error voltage) i s f i l t e r e d by a low-pass loop f i l t e r . The f i l t e r suppresses the noise and also the high-frequency s i g n a l components of the phase e r r o r voltage. The voltage c o n t r o l l e d o s c i l l a t o r i s c o n t r o l l e d by the f i l t e r e d e r r o r voltage V^. The r e l a t i o n s h i p between the VCO output frequen-cy and the c o n t r o l voltage can be expressed as: A w - K QV 2 where: KQ i s the VCO gain constant (radians/sec/V). Since frequency and phase have d i f f e r e n t i a l r e l a t i o n s h i p , the operation of the VCO can be expressed as: dt ° 2 Taking the Laplace transform on the above gives: s 0o(B) - K o V 2 ( s ) K V 0 ( s ) or o This i n d i c a t e s that the VCO acts as an i n t e g r a t o r whose output i s p r o p o r t i o n a l to the i n t e g r a l of the input c o n t r o l voltage. Using Laplace notations, the f o l l o w i n g r e l a t i o -nships are obtained, V d ( s ) - K d( £.(s) - c4 0(s)) , V 2 ( s ) - F ( s ) V d ( s ) , £ Q ( s ) - K o V 2 ( s ) / s These r e s u l t i n the basic loop equations: foil) - H(s) = Ko Kd F< s>  6-£(a) s + K Q K d F ( s ) ,0 ± ( s ) e)i(s) 9 + K o K d F ( s ) The loop f i l t e r F(s) determines the dynamic performance of the loop. 4..1*2.b. THE LOOP FILTER: Two most commonly used loop f i l t e r s are shown i n F i g . ( l l ) with t h e i r respective t r a n s f e r functions. The passive f i l t e r i s simple and i s s a t i s f a c t o r y f o r most appl-i c a t i o n s . The loop t r a n s f e r f u n c t i o n f o r t h i s i s : w , v K o K d < s r2+D/( T± + TZ) s 2 + 8 ( i + K oK d r 2 ) / ( r x + r 2 ) + KoKd/(r1+r2) The a c t i v e f i l t e r requires a high-gain dc ampl-i f i e r but provides better t r a c k i n g performance^^. The loop t r a n s f e r f u n c t i o n f o r t h i s i s : M s ) * 2 + s ( K o K d V ^ l ) + ¥ d ^ l Rewriting the t r a n s f e r functions gives: s(2<w - w2/K K.) + w2  T T / % N ^ n n' o d' n H-^s) -2 o F 2 s + 2\w s + w J n n 2 3 R, R, Passive f i l t e r T F x ( s ) sCR 2 + 1 S T 2 + 1 sC(R 1 + R 2) + 1 Ti - R i c Tz - R 2 c F i g , ( l l a ) ; Passive f i l t e r . R, A c t i v e f i l t e r F 2 ( s ) A(sCR 2 + 1 ) sCR 2 + 1 + (l-A)(sCR 1) F 2 ( s ) = s C R 2 + 1 sT2 + 1 SCR, f o r l arge gain. F i g . ( l i b ) : A c t ive f i l t e r . 24 2 2w <8 + w H 2 ( s ) = " 2 2 s + 2 C w s + w y n n w h e r e : p a s s i v e f i l t e r a c t i v e f i l t e r r i + T 2 > * W n - <KoVTi>* s - « V d ' W 2 ) » V 2 + I A 0 K Q ) J -<V2><KoK<Al> w i t h : w n = t h e " n a t u r a l f r e q u e n c y " o f t h e l o o p * S «* t h e " d a m p i n g f a c t o r " . K Q K d = t h e " l o o p g a i n " ( t i m e ) " 1 . F i g . ( l 2 ) & (13) s h o w t h e f r e q u e n c y r e s p o n s e a n d t h e e r r o r r e s p o n s e o f h i g h - g a i n , s e c o n d - o r d e r l o o p . I t c a n b e s e e n t h a t t h e l o o p a c t s a s a l o w - p a s s f i l t e r o n p h a s e i n p u t s . O n t h e e r r o r r e s p o n s e , a h i g h - p a s s c h a r a c t e r i s t i c s h o w s t h a t t h e l o o p t r a c k s l o w - f r e q u e n c y c h a n g e s b u t c a n n o t t r a c k h i g h f r e q u e n c i e s . O t h e r p o s s i b l e l o o p t y p e s a r e t h e f i r s t - o r d e r l o o p a n d t h e t h i r d o r d e r l o o p . T h e l o o p t r a n s f e r f u n c t i o n f o r t h e f i r s t - o r d e r l o o p i s o f t h e f o r m : H ( s ) = ° d s + K _ K . o d 25 + E + 6 + 4 + 2 0 -L ~A 1 -6 1 - S -10 -12 -14 -16 -18 -20 - • ].! i r.».?.3;.._! ; 1 1 i ' \y^\ 1 ' i ' . ;.: . . ] Ti T 1 L.—'--'-^ i j \ 1 i i i ; : ; ! \ V V \ | \ \ 1 lJ?'r,'<~ \ \ X X - X X . i i i \ i \ K: \ \ S N ' 1 1 0.1 0.2 0.3 0.4 0.5 0.7 1.0 Frequency-w/a>„ 3 4 5 7 10 Fig.{ 1 2 ): Frequency response; h i g h - g a i n , second-order  loop. -10 0.5 1.0 2.0 Frequcncy-u/un 5.0 10 F i g . {13) t E r r o r response of h i g h - f r a i n loop. The loop gain K^K^ i s the only adjustable parameter. For large loop gain, the bandwidth must also be l a r g e . There-fore narrow bandwidth and good tracking are incompatible i n the f i r s t order loop. As f o r the third-order loop, the loop i s unst-able f o r low loop g a i n ^ ^ . Other PLL c h a r a c t e r i s t i c s a n a l y s i s , such as tracking and a c q u i s i t i o n , noise performance, operation of loop components, and loop t e s t i n g , can be found i n r e f e r -ences (6) and (7)» 4.1.3 PHASE-LOCKED LOOP APPLICATIONS: The PLL a p p l i c a t i o n s include r e c e i v e r s , track-ing f i l t e r s , s t a b i l i z a t i o n of o s c i l l a t o r s , frequency mult-i p l i e r s and .dividers, .frequency .translation lo.ops, d i s c r i -minators, and PCM b i t synchronizers, automatic frequency c o n t r o l s , t e l e v i s i o n synchronization and automatic s t e e r i n g of antenna arrays e t c / ^ The p r o p e r t i e s of PLL used i n the present system i s i t s frequency m u l t i p l i c a t i o n a b i l i t y . In t h i s operation, the o s c i l l a t o r i s tuned and locked to one of the harmonics of the input s i g n a l . There i s an upper l i m i t to the frequency m u l t i p l i c a t i o n . This l i m i t i s u s u a l l y below 10 as the frequency approaches the l i m i t of the frequency response of the components. Another arrangement with b e t t e r lock range i s shown i n F i g . ( l 4 ) . The centre frequency of the PLL o s c i l l a t o r i s tuned at N times the input frequency. The output of the VCO i s fed i n t o a counter (-?;N) before being fed into the phase detect-or. The output i s taken from point E. 27 31.5 kc f r o m i c a m e r a Phase detector 1 Loop f i l t e r X N Counter E Fig.( i k ): PLL frequency m u l t i p l i c a t i o n block diagram, In t h i s case, the phase detector i s a c t u a l l y comparing signals of the same frequency. This g r e a t l y i n c r -eases the lock range which i s + 90 degrees of the high f r e -quency i n p u t T h i s method i s adopted i n the present i n t -erface. The IC used i s a S i g n e t i c NE562 open loop mono-l i t h i c PLL. The centre frequency of the VCO i s tuned by one external capacitor. The loop f i l t e r type used i s shown i n Fig.(15). 13 I n R R I _ I Ik 13 NE562 where: R i s between 50 and 200 ohms, x 10 pf 0.12 (2-JTf) Fig.(15): The actual loop f i l t e r used. 28 The c i r c u i t diagram f o r the PLL as a frequency m u l t i p l i e r i s shown i n F i g . ( l 6 ) . To get the m u l t i p l i c a t i o n of 64, one stage of PLL was t r i e d which showed unstable l o c k i n g f o r t h i s high frequency m u l t i p l i c a t i o n . But the PLL showed great l o c k i n g s t a b i l i t y f o r low frequency m u l t i p l i c a t i o n s . Consequently, three stages of PLL are used. Each with a frequency m u l t i -p l i c a t i o n of 4 i n Fig.(17). The t o t a l PLL m u l t i p l i c a t i o n of 64 together with the 31»5 kc from the camera which i s already twice the l i n e frequency gives 128 points per l i n e . Fig.(18), (19), (20) show the outputs of the PLL stages. 29 D.U(f =}= Fig.(16). PLL ( N E 5 6 2 ) frequency m u l t i p l i c a t i o n c i r c u i t diagram. 30 I 31.5 kc From camera x 2 B M x k T 6k H x k x 128 F i g . ( l 7 ) t The PLL frequency m u l t i p l i c a t i o n stages. output A i n p u t from camera F i g . ( 1 8 ) ; F i r s t stage PLL output and 31.5 kc s i g n a l  from camera. ( 2 0 u s e c / d i v , l V / d i v . ) 31 F i g . ( 1 9 ) ; Second stage PLL output waveform and 31 .5 kc  s i g n a l from camera. (10 usec/div., 1 V/cm ) Fig.(20); T h i r d stage I'LL output waveform and 3 1 . 5 kc s i g n a l from camera. ( 5 usee/ d i v . , 1 V/div.) 32 4.2 THE FREQUENCY COUNTER; The output of the frequency m u l t i p l i e r w i l l be divided down by a f i x e d number to generate the sample pulses* As previously c a l c u l a t e d , the countdown needed f o r the d i v -i s i o n i s 319* This countdown.is achieved using a d i g i t a l comparator with one side of the input set at 319 ( = 4 7 7 o c t a l ) . Fig.(21) shows the block diagram of the counter. The other inputs of the d i g i t a l comparator i s fed from the outputs of a synchronous counter which i s clocked by the high frequency output from the frequency m u l t i p l i e r . The output of the d i g -i t a l comparator w i l l go high i f the count from the synchron-ous counter matches the code set at the other inputs of the comparator. The synchronous counter i s used to give f a s t op-er a t i o n to avoid spurious ' g l i t c h e s ' . The one used i s a 93l6 F a i r c h i l d 4-bit synchronous counter. Three of these are casc-aded to provide the 9-bit countdown. The output of the d i g i t a l comparator passes thro-ugh a monostable m u l t i v i b r a t o r which acts as a pulse shaper and the monostable m u l t i v i b r a t o r output i s used to reset the 9316 counters through a b u f f e r c i r c u i t (set of i n v e r t e r s ) . Thus, a narrow pulse i s a v a i l a b l e to reset the counters and gives enough time f o r the system to s e t t l e down before the next count. C a l c u l a t i o n s with the delays caused by each component also ensured that enough time i s a v a i l a b l e f o r the counter to be reset and s t a r t the next counting sequence. The d i g i t a l comparator used i s a 9324 4-bit d i g i t a l compar-ator by F a i r c h i l d . Three such u n i t s are needed f o r 9-bit comparison. 33 The inputs A to the d i g i t a l comparator can be e a s i l y changed to another number to s u i t a p a r t i c u l a r count-down. This gives easy a l t e r a t i o n on the sampling frequency. LSB MSB High i f A»B 1 Mono-stable 1 H i Buffer 1 1 1 1 1 1 0 0 1 = 477(8) A 9324 D i g i t a l comparator 9316 9316 f_EZJ 9316 Master reset B CP from PLL 1 = High l e v e l 0 =» Low l e v e l F i g . ( 2 1 ) t The counter c i r c u i t u t i l i z i n g a d i g i t a l  comparator. 3k k,3 THE SAMPLE-AND-HOLD UNIT; The video s i g n a l from the camera i s sampled by a sample-and-hold u n i t and i t s sampled value held f o r comp-uter storage. F i g . { 2 2 ) & (23) show a schematic diagram of a sample-and-hold u n i t . The requirements to be s a t i s f i e d by the unit are that the sampling window has to be l e s s than 125 ns f o r high r e s o l u t i o n sampling. 50 ns was used. Since the sampling routine takes more than 35 us to complete, the hold c h a r a c t e r i s t i c should have n e g l i g i b l e decay i n 50 us. A Tektronic type 3S76 sampling p l u g - i n u n i t with up to 875 megacycles operating frequency i s used. A DC l e v e l adjust i s a v a i l a b l e on the 3S76 sampling u n i t which provides c o n t r o l f o r the sampled video s i g n a l to the comput-er. An IC S/H i s now a v a i l a b l e f o r 5300 which w i l l replace the 3S76. I t has window of 150 ns. However, time d i d not permit the act u a l replacement. 35 Storage media Analog switch D D i g i t a l c o n t r o l F i g . ( 2 2 ) : Schematic of a sample and hold unit, F i g . ( 2 3 ) ; Sample and hold timing diagram. 36 k\.k AUXILIARY DISPLAY CIRCUITRY; An a u x i l i a r y d i s p l a y c i r c u i t i s included i n the system to monitor the sampling process before i t i s switched to the computer input terminals. The d i s p l a y c i r c u i t i s mainly (8) a standard sawtooth generator^ ' shown i n Fig.( 2 4 ) . The saw-tooth generator i s triggered by the synchronizing s i g n a l s from the camera. Two sawtooth generators are used, i . e . the v e r t i c a l Fig.(25) and the h o r i z o n t a l Fig.(26) sawtooth gene-r a t o r s . Since they are t r i g g e r e d by the h o r i z o n t a l and v e r t -i c a l synchronizing si g n a l s from the camera, a f i x e d time r e l a t i o n s h i p i s maintained between the r a s t e r generated and the sampled video information. As the output of these sawtooth generators are applied to the v e r t i c a l and h o r i z o n t a l d e f l e -ctions of the o s c i l l o s c o p e and the sampled video s i g n a l i s used to modulate the e l e c t r o n beam i n t e n s i t y , a d i g i t a l image i s observed on the CRT screen. Examples of these images are shown i n Fig.(27a) & (27b). I f the d i g i t a l images appear pro-p e r l y sampled, the system i s ready f o r computer input. H sync from camera Horiz o n t a l sawtooth generator X -d e f l e c t i o n s C R T V sync from camera V e r t i c a l sawtooth )^ generator AAAA I n t e n s i t y modulation by the sampled video from: S/H u n i t . y - d e f l e c t i o n s Fig.(2h): The a u x i l i a r y d i s p l a y system 37 V e r t i c a l output V e r t i c a l sync i n Fig. (2$ The v e r t i c a l sawtooth g e n e r a t o r H o r i z o n t a l output AMM/ MPS H o r i z o n t a l <i_ sync i n pip;. (26) : The h o r i z o n t a l sawtooth g e n e r a t o r 38 (b) F i g . ( 2 7 ) : Examples o f s t r o b o s c o p l c a l l y sampled p i c t u r e  d i s p l a y on o s c i l l o s c o p e . 39 4.5 SAMPLING PULSE CONTROL CIRCUIT FOR HIGH RESOLUTION  PICTURES; Attempts were o r i g i n a l l y made to t r y and obtain the high frequency m u l t i p l i c a t i o n using the PLL's. The re-s u l t s were quite unstable and gave poor t r a c k i n g . However, r e s u l t s with the low r e s o l u t i o n p i c t u r e were s u c e s s f u l . Consequently, the following method i s used to get a high r e s o l u t i o n p i c t u r e . A frequency m u l t i p l i c a t i o n of 128 gives 128 points per l i n e . In order to obtain 512 (4*128) points per l i n e high r e s o l u t i o n p i c t u r e , a l o g i c c o n t r o l c i r c u i t i s de-signed with computer c o n t r o l s . This c o n t r o l c i r c u i t with computer controls w i l l delay the sample pulses by 124 us a f -t e r each complete p i c t u r e u n t i l four low r e s o l u t i o n p i c t u r e s are obtained each displaced 124 us from the previous ..one.. By properly i n t e r l e a v i n g the obtained 4 low r e s o l u t i o n p i c -tures i n the computer, one would get an equivalent of 512*525 points high r e s o l u t i o n p i c t u r e . A delay c i r c u i t such as the one shown i n Fig.(28) i s used. I t consists of 2 monostable m u l t i v i b r a t o r s i n tan-dem. The f i r s t one acts as a pulse s t r e t c h e r . The second one acts as a delayed pulse generator. The operation can be understood by examining the accompanied timing diagram i n Fig.(28). Capacitors C^ and are the external timing cap-a c i t o r s c o n t r o l l i n g the amount of delays i n the c i r c u i t . The sampling pulses are fed i n t o 3 such delay c i r c u i t s with delays of 124 ns, 248 ns, 372 ns. The reason f o r these delays i s that the normal sampling r e s o l u t i o n i s ko k$6 ns. To get 3 more pictures uniformly along the l i n e , each has to be s h i f t e d by k$6/k ns with the previous one. This r e s u l t s i n k sets of sampling pulses with a f i x e d phase r e l a t i o n s h i p with each other. They are then fed i n t o a gated NAND gate which i s c o n t r o l l e d by the computer d i g i t a l output terminals. As can be seen from F i g . ( 2 9 ) , sample pulse w i l l go through the NAND gate i f goes high and the rest of the controls are low, so that only one kind of sampling pulses i s allowed through the gate. A f t e r the f i r s t p i c t u r e storage, the computer can s t a r t the next p i c -ture by s e t t i n g high and C^, C^, low. For subsequent p i c t u r e s , w i l l go through i f i s high, and the rest of the controls are low. w i l l go through i f i s high and the rest of the controls are low. The integrated c i r c u i t s used are the MC8601 monostable m u l t i v i b r a t o r s and the 74H20 four input NAND gates. kl C l R x CC H L P T l T 2 A .—5-H d Q Q B MC8601 H G 2 R x V — \ A A A / O CC T O r i g i n a l pulse set by C. Stretched pulse 1 set by C., Delayed pulse Timing diagram Fig,(28); The m u l t i v i b r a t o r delay c i r c u i t s F i g . ( 2 9 ) : Sampling pulse c o n t r o l c i r c u i t with computer c o n t r o l s . 43 5'. PROGRAMMING TECHNIQUES A PDP-12 computer i s used i n the present system. The computer system d e s c r i p t i o n i s included i n Appendix 2. There are eight programs w r i t t e n f o r data inputs, d i s p l a y s , and manipulations. Descriptions of the programs are given i n the following sections. 5.1 INPUTl; This program stores the incoming information on core and then t r a n s f e r s the data in t o d i s c 2k (lk=1024 12-b i t words) at a time. Disc tracks 1000-3060(8) are used as permanent storage. Data; f i e l d 1 i s used as temporary data storage. A f t e r the f i r s t 2k data i s f u l l , a d i s c i n s t r u c t -i o n i s executed. Without waiting f o r d i s c completion, the next 4k i s being f i l l e d up at the same time while the d i s c i s simultaneously s t o r i n g the previous 2k data. Since i t takes 340 ms to f i l l 2k of core memory of data and i t req-u i r e s 160 ms to tr a n s f e r 2k of data into d i s c , the t r a n s f e r of data onto the d i s c w i l l be f i n i s h e d long before the next 2k of core i s f u l l . This w i l l guarantee that the sampling and s t o r i n g operations occur simultaneously while the proper time i n t e r v a l i s a v a i l a b l e f o r completion. This operation alternates between the two 2k blocks of core memory. The purpose of t h i s i s to speed up the sampling frequency and to reduce the input time. The i n s t r u c t i o n SAM 14 samples the data term-i n a l l 4 and converts the r e s u l t i n t o a number ranging from 777 to -777 o c t a l . The input s i g n a l has to be wi t h i n + 1 V to be completely sampled and stored. kk The execution time of the longest loop (l40 us approx.) i n the program determines the sampling frequency. The sampling frequency were also r e s t r i c t e d by the c o n d i t i o n that- the countdown has to be prime with the t o t a l number of points i n the p i c t u r e . A compromise was found to be f » 6 kc. s A proper sampling frequency i s v i t a l since the program can-not a f f o r d to miss a s i n g l e sample. Three inputs to the computer are required f o r t h i s program. They are the s t a r t - o f - p i c t u r e pulse, the sample pulses and the sampled video. A flow chart i s shown i n F i g . ( 3 0 ) . 5.2 0UT1; A f t e r the p i c t u r e information i s stored on d i s c , the program 0UT1 i s run to d i s p l a y the p i c t u r e on the CRT (VR12) d i s p l a y . The data are transferred'from the d i s c 4k words each time and then displayed. The samples are displayed i n the same fashion as they were stored. The VR12 CRT d i s p l a y i s a point d i s p l a y with 512x512 addressable points, F i g . ( 3 l ) . The p o s i t i o n of a point displayed can be c a l c u l a t e d from the previous l o c a t i o n which i s M points away. This r e s u l t s i n a d i s p l a y which i s stroboscopic. A one cycle time exposed p i c -ture can be taken to evaluate the q u a l i t y of the input i n f o -rmation to make sure that a l l points are stored. A binary and a m u l t i - l e v e l d i s p l a y are a v a i l a b l e . For most operations, a binary d i s p l a y i s enough which also reduces d i s p l a y time. Since the d i s p l a y u n i t has a poor grey l e v e l , a time i n t e g -r a t i o n i s used to achieve a m u l t i - l e v e l p i c t u r e . The p i c t u r e s show acceptable signal-to-noise performance. Dot, I _ set sampling pulses 45 load DATA f i e l d 2 set c(store)=2000 set f a s t sampling mode C(DF ) = 6 4 2 no Dot<— •sample data terminal ik f store data the store 2 k on d i s c yes Jan.. yes JL set sample pulses return to d i a l i Dot F i g . (30' ; Flow diagram f o r INPUT1. 46 The following sense switches are a v a i l a b l e f o r program c o n t r o l : Sense switch No. 0: set to h a l t a f t e r one cycle d i s p l a y . Sense switch No. 2: set to d i s p l a y a l l p o i n t s . Sense switch No. 3 s set to give a negative d i s p l a y . Sense switch No. 4: set to give a video d i s p l a y . Sense switch No. 5: set to return to d i a l a f t e r one cycl e d i s p l a y . 0,377 0,-377 777,377 777,0 777,-377 F i g . ( 3 1 ) t The CRT g r i d . The binary threshold i s also v a r i a b l e by chang-ing a parameter i n the program. A flow diagram of 0UT1 i s shown i n Fig.(32) & (33). 5.3 MAN2: Since stroboscopic sampling was used, the data stored w i l l not be i n a sequential order. But before any processing can be done on the p i c t u r e information, the data can be rearranged i n t o a sequential order. The program MAN2 rearranges the input data i n t o a usable form. The new addr-ess f o r the samples can be c a l c u l a t e d as follows: DISPLA, s t a r t s e t : s t o r e = 2 0 0 0 L = l G l 5 ( 5 2 5 i n ) X = - 2 3 7 ^ = (-M) Y = - 3 3 7 M = 2 3 7 ; + ( l 3 3 l i n ) 0 = 6 7 7 7 ( 5 1 2 Q7 COORD, Jmp COORD i n c r e a s e X b y M Jmp CONT 5- Jmp CONT decrea.se C ( y ) by 2\ 6 <»7 d e c r e a s e C ( L ) b y 2 a d d C t o C ( X ) J VIDEO, b i t c l e a r 7 0 0 0 ~ I i r e s n o d i s p l a y d o t and i n c r e m e n t X Jmo NEXT F i g , ( l i : Plov; d i a g r a m f o r 0UT1. 4 8 CONT, iCLE A.R | i \ / load data into AC NEXT, Jmp VIDEO NEXT put c(n6) = - l ! get Y and j di s p l a y C ( R 6 ) | times ) V NEXT load C { L ) yes no add XY to L and store i n Y I reset L to (1015+L) I l o a d data address |_ into AC _____ Jmp DISPLAY no get'more | data \ Fig . ( 3 3 ) ; Cont'ed flov: diagram f o r 0IJT1. 49 L o c ( i ) L o c ( i - l ) + M where: Loc(i) i s the memory address f o r the i t h sample. L o c ( i - l ) i s the memory address f o r the ( i - l ) t h sample* M i s the number of p i c t u r e points between adjacent sampleso(i.e. the countdown). Using the above formula, new data are stored i n d i s c address 3100-5160(8), a f a i r amount of data t r a n s f e r has to be done between the core and the d i s c . Since the d i s c u t i l i z e s a servo mechanism which has a f i n i t e response time, a large amount of program execution i s due to the d i s c . In t h i s program, segment 1 i s used f o r storage of old data i n LINC mode operation. Data f i e l d 1 i s used as the temporary storage of new rearranged data. A flow chart of M A N 2 i s shown i n Fig.(3 4 ) . 4 low r e s o l u t i o n p i c t u r e s stored s e q u e n t i a l l y on the d i s c * Each low.resolution p i c t u r e i s a v a i l a b l e f o r processing. The program DIP1 di s p l a y s the p i c t u r e s e q u e n t i a l l y . Each consecutive p i c t u r e i s displayed with a d i f f e r e n t o r i g i n a l x co-ordinates so as to give a high r e s o l u t i o n p i c t u r e as follows: 5.4 DIP1: The execution of the program* M A N 2 r e s u l t s i n 1234123412341234 l i n e d i s p l a y 1 - f i r s t p i c t u r e » 3 - t h i r d p i c t u r e , 2-second p i c t u r e 4-fourth p i c t u r e . s t a r t j i n i t i a l i z e d i s c I and v a r i a b l e s [and D F 1 0  no l o a d 11c d a t a i n t o D F 2 from d i s c > — X , address=address + Ml l o a d DF 1 0 < ^ s t o r e i t no -test o l d ^v^^^ d a t a addres^" = 3777 ? \ yes Q Y s t o r e 4 k of DF 10 i n t o d i s c r e s e t d i s c a d d r e sses r e s e t d i s c a ddress 50 read 4 k j from d i s c i n t o t=t-DF10 j get new address F i g * (34) : Flow diagram o f MAN2. 51 Since the d i s p l a y i s sequential, the program i s considerably s i m p l i f i e d . See Fig.(35)• 5.5 INTBRl: I f processing on a 512x525 d i g i t a l p i c t u r e i s required, the program INTERl w i l l i n t e r l a c e the low r e s o l u -t i o n p i c t u r e s r e s u l t e d from MAN2 to provide one s e q u e n t i a l l y stored high r e s o l u t i o n p i c t u r e . The new p i c t u r e w i l l be stored s t a r t i n g d i s c track address 1000. The execution of the pro-gram INTERl r e s u l t s i n an odd and even frame of high r e s o l u -t i o n p i c t u r e , 5.6 IIP3: The program HP3 d i s p l a y s the odd, then even frames of the high r e s o l u t i o n p i c t u r e a f t e r the program INTERl, Fig.(36). 5.7 INTER2: The program INTER2 puts the odd; and even frames i n an i n t e r l a c e d manner r e s u l t i n g i n a 512x525 high r e s o l u -t i o n p i c t u r e . 5.8 HP4: The program HPk d i s p l a y s the high r e s o l u t i o n p i c t u r e r e s u l t i n g from INTER2. Controls are a v a i l a b l e f o r d i s p l a y i n g p o s i t i v e p i c t u r e , negative p i c t u r e , a l l points d i s p l a y , contour d i s p l a y Fig,(37), one cycle d i s p l a y , etc. A l l the above d i s p l a y s show acceptable s i g n a l -to-noise performance. However, as can be seen from the top and bottom of the page d i s p l a y i n Fig.(35), some white areas have turned black. This introduces errors i n the p i c t u r e . This i s due to the n o n l i n e a r i t y across the V i d i c o n screen. Necessary program may be developed to compensate f o r t h i s n o n l i n e a r i t y . 53 ( a ) . The c h a r a c t e r 'b' ( b ) . A p r i n t e d page F i f i . ( 3 5 ) : P i c t u r e d i s p l a y f o r DIP1 Fig,(37); E x a m p l e of a c o n t o u r d i s p l a y . 55 6. READING ASSIST DEVICES FOR PEOPLE WITH LOW VISION A large p o r t i o n of the b l i n d population belongs to those with severely impaired v i s i o n , whose eye-sights have not been completely l o s t . This group consists mainly of older people whose eye-sights decline due to aging. As t h i s group belongs to a considerable part of the b l i n d pop-u l a t i o n , more e f f o r t s should be devoted to designing read-ing aids f o r the low-visions. This leads to the development of image enlargers. Recently, a commercially made closed c i r c u i t t e l e v i s i o n system has been made a v a i l a b l e as an image en-l a r g e r . A t e l e v i s i o n camera i s mounted on a s l i d e rack over the reading materials and the user simply scans the camera across the document and observes the d i s p l a y on t h e . t e l e -v i s i o n monitor. This helps the p a r t i a l l y - b l i n d e d user to a c e r t a i n extent. However, the image observed on the monitor i s the same as the image picked up by the camera which con-s i s t s of sections of p r i n t l i n e s . Only a p o r t i o n of the view i s meaningful to the user. A way to increase the reading e f f i c i e n c y of such an image enlarger would be to d i s p l a y a whole p r i n t l i n e on the monitor where the whole monitor d i s p l a y i s meaningful to the reader. This has to be done on a d i g i t a l p i c t u r e stored i n a computer where the computer has c o n t r o l over the p o r t i o n of the p i c t u r e displayed. The d i s p l a y process i s i l l u s t r a t e d i n F i g . ( 3 8 ) . The d i g i t a l p r i n t l i n e w i l l be sectioned i n t o h parts and then displayed one above the other i n the manner 56 below. In t h i s way, the whole p r i n t l i n e appears on the e n t i r e screen which the user finds meaningful. A program i s w r i t t e n to t h i s purpose. The p i c -ture i s being displayed on the VR12 CRT d i s p l a y . Display examples are shown i n Fig,(38a) and (38b). To d i s p l a y the next p r i n t l i n e , the user merely presses a key. The next p r i n t l i n e w i l l be displayed i n l i k e manners i n f r a c t i o n s of a second. In using the system, the distance between the camera and the materials being read has to be f i x e d . I t also appears that a storage CRT d i s p l a y u n i t might be necessary due to the slovr rate of d i s p l a y refreshment by the computer. Provisions should also be made to r e p o s i t i o n the slanted p r i n t l i n e s . ''ig. ( 3 8 a ) : P o s i t i v e d i s p l a y example ol' r e a r r a n g e d ;»rint l i n e . 7 . FOCUS CONSIDERATIONS I t i s obvious that any o p t i c a l image system must be c o r r e c t l y focused to y i e l d the proper performance. This s e c t i o n describes some image properties r e l a t e d to focus. In order to make a b l i n d person as independent as pos s i b l e i n using a reading device, i t i s h i g h l y d e s i r a b l e to incorporate an automatic focusing f u n c t i o n a l u n i t i n the system. But before such a u n i t can be b u i l t , an algorithm has to be developed to provide a ra p i d and accurate i n d i c -a t i o n of focus. The algorithm should be simple enough that i t could be e f f i c i e n t l y incorporated i n a real-time, on-l i n e focusing device, 7 e l PROPERTIES OF FOCUS; Much work.on focus .mechanism has been done i n the area of human chromsome research. There i s a need i n t h i s area f o r automatic focus. In microscopic images the depth of f i e l d i s i n the order of microns. Research i n t h i s area has shone much l i g h t on the area of automatic focusing. The following s e c t i o n describes some of t h e i r f i n d i n g s • I t was observed experimentally that focus i s c l o s e l y r e l a t e d to other o p t i c a l image properties as w e l l . Properties such as area, contrast, and edge sharpness are a l l dramatic functions of f o c u s w / . Attempts were made to r e l a t e these properties i n mathematical terms. A f u n c t i o n r e l a t e d to the greyness or o p t i c a l density of the image was tested and found to be extremely s e n s i t i v e to the above p r o p e r t i e s . The function i s defined as follows: n F = 2~» (OD -f) f o r a l l OD > f . i where: OD^ i s the greyness at a point ( O p t i c a l d e n s i t y ) . n i s the number of points i n the image with 0 D ±> f . *jf i s a reference threshold a r b i t r a r y f i x e d at an o p t i c a l density mid-range of image greyness. With experiments done on microscopic chromosome images, such a function was found to e x h i b i t a s e n s i t i v i t y i n measurement g r e a t l y exceeding that of manual focusing. I t i s sa i d to be a p p l i c a b l e to both microscopic and macro-scopic imaging problems^ 1 0). To understand the underlying p r i n c i p l e behind i t , i t i s best to look at the greyness p r o f i l e versus focus curve. F i g . ( 3 9 ) shows such a curve with OD as ordinate and distance as abscissa. Curve 1 i s a properly focused image. Curve 2 represents an image which i s at l e s s than optimum focus. As i t can be seen, the focus g r e a t l y a f f e c t s the greyness d i s t r i b u t i o n of the image. But defocusing and focusing leaves the t o t a l area under the curve v i r t u a l l y unchanged. This i s due to the f a c t that the t o t a l area und-er the curve represents ^(OD) which i s known to be i n -s e n s i t i v e to objective height or focus. Proper focus causes the OD to p i l e up toward the axis of a chromosome image, whereas poor focus causes a d i s p e r s i o n of the OD away from 60 the a x i s . To reveal f u r t h e r d i f f e r e n c e s between the curves, a threshold i s drawn i n the mid-range of the greyness s c a l e . I t i s c l e a r that the area between the curve and the thres-hold f o r the focused image i s considerably greater than that of the defocused image. This i s true regardless of where the threshold i s placed above the background. Such an area can be w r i t t e n as (OD - 'f) f o r a l l OD > ~f. Thus by adjust-ing the focus and at the same time computing the value f o r the F f u n c t i o n w i l l eventually obtain optimum focus by maximizing F. 7 . 2 A PROPOSED METHOD FOR THE PRESENT SYSTEM (THE T FUNCTION) Many methods have been suggested f o r implemen-t a t i n g automatic focus (9*10,11,12,13). A s t a t i s t i c a l method has been proposed here which i s simple to instrument and i s s u i t e d to the present i n t e r f a c e . Consecutive samples such as e^ and e^ are shown i n Fig.(40). In out-of-focus, the extre-mes i n e^ and w i l l be reduced, and i n the l i m i t f o r com-p l e t e l y out-of-focus adjustment, the s i g n a l at each point of the camera mozaic w i l l be the same corresponding to equal grey i l l u m i n a t i o n , ^"^ je^ - e.J = 0. As the image i s brought int o focus, Je^ - e^J > 0. I f a number of such points i s taken, then a measure y j A e _ | n T can be formed which w i l l be maximum f o r " i n focus" conditions. This i s a s t a t i s t i c a l measure i n the sense that patterns can be produced f o r which T shows no maximum. Simple examples are a l l white or a l l black f i e l d s . However, the patterns to be used with t h i s i n t e r f a c e correspond to black p r i n t on white background, Fig. ( k O ): Two samples of the video s i g n a l . 62 f o r a n o r m a l l y " f u l l " f i e l d . F i g . ( 3 9 ) a l s o shows t h a t the s l o p e o f the curve f o r the f o c u s e d image i s g r e a t e r than t h a t o f curve f o r d e f o c u s e d image. T h e r e f o r e , a f u n c t i o n r e l a t e d t o the d i f f e r e n c e i n greyness would be s e n s i t i v e t o f o c u s as w e l l . The T f u n c t i o n i s d e f i n e d as f o l l o w s ? T - £ |AeJ i 1 1 where: Ae^ i s the d i f f e r e n c e i n greyness between any two p o i n t s . n i s the number o f p o i n t s i n the summation. |A e .J i s the a b s o l u t e v a l u e o f |/\ e j . The f u n c t i o n T has no t h r e s h o l d i n v o l v e d . T h i s s h o u l d p r o v i d e more i n f o r m a t i o n s i n c e i n the p r e v i o u s case f o r the f u n c t i o n F, the i n f o r m a t i o n below the t h r e s h o l d has been c o m p l e t e l y d i s r e g a r d e d . 7.2.a. SOFTWARE IMPLEMENTATION OF T FUNCTION: Ne c e s s a r y programs a r e de v e l o p e d t o c a l c u l a t e the value, f o r the T f u n c t i o n w i t h double p r e c i s i o n u s i n g n«2000 p o i n t s . The s t r o b o s c o p i c a l l y sampled i n p u t was used and c o n s e c u t i v e samples a r e s u b t r a c t e d and the a b s o l u t e v a l u e o f the r e s u l t s a re added t o g e t h e r . A f l o w diagram f o r the program i s shown i n F i g . ^ 4 l ) . 7..2.b. EXPERIMENTAL RESULTS ON THE T FUNCTION: Such a f u n c t i o n i s b e i n g e x p e r i m e n t a l l y t e s t e d on the TV camera u s i n g the PDP-12 computer t o compute i t s 63 value while manually changing the focus adjustment. The r e s u l t s are shown i n F i g . ( 4 2 ) & ( 4 3 ) f o r d i f f e r e n t p r i n t materials. The r e s u l t s i n d i c a t e that the fun c t i o n shows prominent optimum f o r a printed page image, but i t shows l i t t l e or no maximum f o r the b i g l e t t e r 'b 1. This can be. explained by the f a c t that since the f u n c t i o n i s r e l a t e d to the d i f f e r e n c e i n greyness between sample points, the c l o s e r the percentage of black area to white area, the more s e n s i t i v e i s the fun c t i o n T to focus. This i s true f o r the p r i n t e d page while the opposite i s true f o r the b i g l e t t e r *b'. As the image conies i n focus, the black areas appear blacker, while the white areas become whiter, t h i s r e s u l t s i n a l a r g e r A e . S i m i l a r reasoning leads to the conclusion that the square of the d i f f e r e n c e i n greyness should show even stronger dependence on focus. n S x where: A e_ i s * n e d i f f e r e n c e i n greyness. n i s the number of image points included i n the summation. s t a r t 6k v g e t d i g i t a l p i c t u r e j i n c o r e memory i get one sample into A C make negative j index sample address • and add next point j into A C p r i n t out r e s u l t T j MALT F i g , (kj) : Flow diagram f o r computing the T f u n c t i o n . 65 1600 1500 ikoo FOCUSED -4- -10—FT. Fig.(42); The 'T1 curve f o r p r i n t e d page. r e l a t i v e e 1600 1400 1200 1000 FOCUSED t 8 12 15 20 * FT. F i g . (43): The 'T' curve f o r the l e t t e r 'b»'. 66 8. CONCLUSIONS The input stage of a TV-computer reading a i d system has been b u i l t . The performance of the hardware shows t o l e r a b l e s i g nal-to-noise performance f o r reading a i d a p p l i c a t i o n s , see s e c t i o n 5.2 and Fig,(35), The use of a TV camera as an input element appears j u s t i f i e d , . Since stroboscopic sampling i s used, necessary programs are developed to rearrange and d i s p l a y the d i g i t a l information f o r processing purposes. The disadvantage of the sampling scheme i s that much time i s needed to rearran-ge the s t r o b o s c o p i c a l l y sampled data due to the f i n i t e r e s -ponse time of the d i s c . This renders the sampling scheme im p r a c t i c a l f o r a computer with a d i s c as storage medium but i t should show acceptable performance f o r computer with enough core memory. However, a change i n the sampling scheme should improve the system tremendously.(Suggestion 8.1) Such a system can be used as an image enlarger or as a reading device f o r people with low v i s i o n . For the former, the p r i n t l i n e i s enlarged and rearranged to appear e n t i r e l y on the monitor. The user presses a button to read the next p r i n t l i n e on the monitor. However, due to the non-l i n e a r i t y on the greyness l e v e l i n the Vidicon, some p i c t u r e degradation i s observable. This makes some areas appear whiter than other areas of the same act u a l whiteness. But the degradation can be reduced or eliminated by developing program to compensate properly f o r the n o n l i n e a r i t y i n the Vidicon. 67 To eliminate the need f o r a b l i n d user to adjust the focus,, a focus a s s i s t algorithm (the T function) i s exa-mined and shows i t s e l f to be very s e n s i t i v e to focus. This i s a rather simple f u n c t i o n and can e a s i l y be implemented i n the system to c o n t r o l the focus a s s i s t devices. The pre-sent sampling scheme i s p a r t i c u l a r l y s uited to the T f u n c t i o n since the focus can be obtained without having to input the e n t i r e p i c t u r e . This i s because the stroboscopic samples are scattered over the e n t i r e p i c t u r e and the number of summation n can be set at a f i n i t e f i x e d number. Due to the s i m p l i c i t y of the hardware system, the cost i s estimated at about $k00 which i s f a i r l y low even on a p e r - i n s t a l l a t i o n b a s i s . However, some improve-ments are needed to make the system more e f f i c i e n t which may increase the cost of the system. The followings are some suggestions f o r improving a TV-computer reading systems 8.1 A l i n e input scheme. In t h i s scheme, a TV p i c t u r e scan l i n e i s samp-l e d and s h i f t e d i n t o a l i n e r e g i s t e r to wait f o r computer ing e s t i o n ; The information on the l i n e r e g i s t e r i s then s h i f t e d out 12-bit at a time f o r acceptance by a 12-bit word computer. This method has the advantage that the l i n e s are input i n t o the computer as a whole sequential l i n e . The next sampled l i n e i s several l i n e s away from the previous one. The number of l i n e s between input l i n e s are determined by the time taken by the computer to ingest the l i n e i n f o r -mation temporarily stored i n the l i n e r e g i s t e r . The l i n e s can e a s i l y be rearranged by programming the l i n e storage address corresponding to steps of the same number. Another method of l i n e i n p u t t i n g i s to input consecutive l i n e s of the p i c t u r e . This w i l l increase the input time but w i l l also eliminate programs f o r rearrang-ing the l i n e s . 8.2 Replacement of the Tektronic S/H p l u g - i n  uni t by I C 1 s . The present system u t i l i z e s the 3S76 p l u g - i n uni t as a S/H device. This should be replaced by an IC to reduce the s i z e of the i n t e r f a c e i f S/H with better sampl-ing window are commercially a v a i l a b l e . 8.3 The a d d i t i o n of a zoom lens . With a zoom lens included i n the camera, the system can be used to read not only large s i z e p r i n t s , but also small s i z e p r i n t s . 8.4 The i n c l u s i o n of a f o c u s - a s s i s t servo mech- anism. Such a f o c u s - a s s i s t device w i l l be c o n t r o l l e d by the computed T f u n c t i o n to obtain the optimum focus f o r the camera. 69 BIBLIOGRAPHY: 1. NYE P.W. BLISS J.C. "SENSORY AIDS FOR THE BLIND". IEEE PROCEEDINGS. VOL.58, NO. 12, D e c , 1970. 2. SLOAN COMMISSION REPORT: "ON THE CABLE - THE TELEVISION OF ABUNDANCE". McGraw-Hill Book Company. 1971. 3. COMPUTER, IEEE COMPUTER SOCIETY. March 1973, P» 47. 4. TROXEL D.E., LEE F.F., MASON S.J. "COGNITIVE INFORMAT-ION PROCESSING". QUARTERLY PRESS REPORT NO.94, RESEARCH LABORATORY OF ELECTRONICS, M.I.T., J u l y 15, 1969. 5. "VIDEO COMPRESSOR INSTRUCTION MANUAL", COLORADO VIDEO, INCORPORATED. BOULDER, COLORADO, Jan. 1973. 6<. GARDNER F.M. "PHASELOCK TECHNIQUES". John Wiley & Sons, Inc. 1966. 7. KLAPPER J . , FRANXLE J.T. "PHASE-LOCKED AND FREQUENCY-FEEDBACK SYSTEMS". ACADEMIC PRESS, N.Y. & LONDON, 1972, 8. ELECTRONICS HANDBOOK OF CIRCUIT DESIGN. McGRAW-HILL PUBLICATION. 9. MENDELSOHN M.L., MAYALL B.H. "COMPUTER-ORIENTED ANALYSIS OF HUMAN CHROMOSOMES -3 FOCUS". COMP. BIOL. MED. VOL.2,1972, pp. 137-150. 10. MENDELSOHN M.L. ET AL. "FOCUS-ASSIST DEVICE FOR A FLYING-SPOT MICROSCOPE". IEEE TRANSACTION ON BIOMEDICAL ENGINEERING, VOL.BME-20,WO.2,March 1973,PP.126-132. 11. BAXTER L. ET. AL. "NEW PRINCIPLE FOR FOCUSING A HIGH-POWER MICROSCOPE AND MEANS FOR ACCOMPLISHING-THE FOCUSING AUTOMATICALLY AND WITH GREAT ACCU-RACY". J.OPT.SOC.AM. 47,76(1957). 12. STEEL W.H. "PRECISION FOCUSING WITH PHOTOELECTRON DET-ECTION". J.OPT.SOG.AM. 52,1153(1962). 13. KUJOORY M.A., MAYALL B.H. AND MENDELSOHN M.L. " FOCUS-ASSIST DEVICE FOR A FLYING SPOT MICROSCOPE", IEEE TRANSACTION, G-BME (1972). 14. ANNER G.E. "ELEMENTS OF TELEVISION SYSTEMS". Pr e n t i c e -H a l l Inc., N.Y. 1951. 15. ROSENFELD A. "PICTURE PROCESSING BY COMPUTER". Academic press, 1969. 70 16. ANDREWS H.C. "COMPUTER TECHNIQUES IN IMAGE PROCESSING" Academic press, 1970. N.Y. & LONDON. 17. GOURIET G.G. "A METHOD OF MEASURING TELEVISION PICTURE DETAIL", ELECTRONIC ENGINEERING, J u l y , 1952, pp. 308-311. 18. BARER R. & COSSLETT V.E. "ADVANCES IN OPTICAL AND ELEC-TRON MICROSCOPY" -, VOL. 2, Academic press, 1968. 71 APPENDIX APPENDIX 1 TECHNICAL INFORMATION ON THE SYSTEM: The camera used i n the present system i s a Sony model 2000. I t has 1.5 f t to i n f i n i t y focus range and 1.8 to 16 aperture range. The aperture i s set at a f i x e d value (2.8) i n conjunction with the l i g h t i n g u n i t f o r the p r i n t e d m a t e r i a l . The s e n s i t i v i t y of the camera c o n t r o l switches i s set at •automatic* instead of 'manual 1. Therefore,no f u r t h e r adjustment i s necessary on the camera save f o r the incorpo-r a t i o n of a p o s s i b l e zoom lens complex. 73 APPENDIX 2 COMPUTER SYSTEM DESCRIPTION: The computer system used i s a PDP-12 computer manufactured by the D i g i t a l Equipment Corporation. This i s a minicomputer with 8k 12-bit word core memory. The core memory has a cycle time of 1 .6 us and i s expandable to a maximum of 32k words. I t i s mainly a laboratory computer. The computer has two modes of operation, i . e . the LINC mode and the PDP mode. Most of the input-output ( i / o ) i n s t r u c t i o n s belongs to the LINC mode. In the LINC mode, c a l c u l a t i o n s are done using l ' s complement arithematic with 10-bit address indexing. The whole set of i n s t r u c t i o n f o r the LINC -8 computer are a v a i l a b l e i n t h i s mode of operation. In the PDP-8 mode, the computer operates the same as a PDP-8 computer as that PDP-8 i n s t r u c t i o n s sets are a p p l i c a b l e . Most of the programs are w r i t t e n i n the PDP mode, except of course, the i/O rout-ines which are i n the LINC mode. This has the advantage of being able to replace the u n i t by a smaller PDP-8 computer with l i t t l e programming mod i f i c a t i o n s . The computer can be switched from one mode i n t o another accompanied by a t r i f l e delay (1 . 6 us) i n program executions. For each mode, the memory organizations are d i f f e r e n t as shown i n F i g . ( k k ) & (^5). The PDP-12 computer presently includes a VR12 CRT point d i s p l a y , two TU55 t r a n -sport u n i t s , 16 analog inputs feeding a 10-bit analog-to-d i g i t a l converter, a d i g i t a l - t o - a n a l o g converter, a 12-bit d i g i t a l output terminal, 12 d i g i t a l sense l i n e s , 6 r e l a y s 74. and a Model ASR 33 t e l e t y p e c o n t r o l . I t a l s o i n c l u d e s a FPP-12 f l o a t i n g p o i n t p r o c e s s o r f o r h i g h p r e c i s i o n c a l c u -l a t i o n s . The system u t i l i z e s a RK08 magnetic d i s c u n i t as an a u x i l i a r y s t o r a g e u n i t which i s c a p a b l e o f s t o r i n g 800k-words o f d a t a . The d i s c u n i t u t i l i z e s the d a t a break f a c i l -i t y f o r d a t a t r a n s f e r . 1777 -*• SEGMENT 0 4 20Q0 * 1 5 it 2 6 3 7 7777 10000 -17777 Fig.(4 4 )• LINC mode memory o r g a n i z a t i o n 0000 II 1777-2000 1 DAT-/ FIE] \. LD 0 DA' FI] rA £LD 1 -10000 7777 1^7777 Fig. ( 4 5): PDP mode memory o r g a n i z a t i o n 

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