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A television camera to computer interface 1970

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A TELEVISION CAMERA TO COMPUTER INTERFACE by TUNDEY YUSUF B.Sc. U n i v e r s i t y o f W a l e s , Swansea, 1968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n t h e Department o f E l e c t r i c a l E n g i n e e r i n g We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d R e s e a r c h S u p e r v i s o r Members o f t h e Committee A c t i n g Head o f the Department Members o f t h e Department o f E l e c t r i c a l E n g i n e e r i n g THE UNIVERSITY OF BRITISH COLUMBIA A u g u s t , 1970 In 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 a d v a n c e d d e g r e e 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 , I a g r e e t h a t t h e 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 a g r e e 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 t h e Head o f my Depar tment 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 no 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 . Depa r tment The 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 V a n c o u v e r 8, Canada ABSTRACT . This i s an instrumentation t h e s i s . The i n t e r f a c e system discussed i s a l i n k between an ordinary TV camera and a computer f o r storage of v i s u a l data. The same system can also be used as a l i n k between the computer and a d i s p l a y monitor. Because of i t s wide bandwidth, a video s i g n a l cannot be sampled at the Nyquist rate and presented to a computer. Previous i n t e r f a c e systems overcame the problem by scanning slowly on an .element-by-element basis using a s p e c i a l scanner and then presenting the samples to the computer. A f t e r processing, the data would be read out at the same slow rate and displayed on a s p e c i a l d i s p l a y monitor. The i n t e r f a c e described i n t h i s thesis w i l l accept material obtained from an ordinary TV camera scanning at standard rate. By using a "stroboscope" sampling technique the samples are pre- sented to the computer slowly enough f o r i t to process. A f t e r processing, the data i s displayed i n a s i m i l a r manner on a normally scanned monitor f o r evaluation. B a s i c a l l y the i n t e r f a c e operates as follows: A TV camera vid-ao s i g n a l i s sampled at a rate slow enough f or i computer acceptance. The camera scans the same p i c t u r e several hundred times u n t i l a l l the points representing the p i c t u r e have been sampled and stored, the sampling i s c o n t r o l l e d such that a l l the points are each sampled only once. Because of the sampling method consecutive samples i n the computer do not correspond to adjacent points on the p i c t u r e being stored. I t may therefore be necessary to programme the computer to arrange the samples such that adjacent data i n the computer represent consecutive p i c t u r e points before processing. A f t e r processing, the samples may be rearranged and read out f o r dis p l a y i n the same order they were stored. i i The h o r i z o n t a l r e s o l u t i o n of the p i c t u r e being stored can be var i e d quite e a s i l y i n steps. For example, a system designed to have a maximum of 480 p o i n t s / l i n e w i l l also have the a b i l i t y to provide such lower r e s o l u t i o n s as 60, 120 and 240 p o i n t s / l i n e s . This v a r i a t i o n i s made po s s i b l e by the design of the hardware. By software the v e r t i c a l r e s o l u t i o n can be va r i e d between an upper l i m i t of 525 l i n e s per p i c t u r e and such near submultiples of t h i s as 263 and 131 l i n e s / p i c t u r e . The thesis i s discussed i n r e l a t i o n to the PDP-9 computer on which most of the work described was done. However, the system i n t e r f a c e s r e a d i l y with other computers. i i i TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS i v LIST OF ILLUSTRATIONS v 1. INTRODUCTION 1 1.1 Previous Interface Systems 1 1.2 The New Interface System 2 2. HARDWARE REALIZATION . . 7 2.1 The Storage System 7 2.2 The Display System 15 3. PROGRAMMING TECHNIQUES . 23 3.1 Coarse Quantization 24 3.2 Storage Programme f o r 7-bit Quantization 26 3.3 The Display Prograjnme 28 4. PERFORMANCE TESTS 31 4.1 Q u a l i t a t i v e Tests 31 4.2 Quantitative Tests 35 5. SUMMARY AND CONCLUSIONS 36 5.1 Limitations 36 5.2 Methods of Improvements 37 5.3 Possible Uses 40 APPENDICES 41 BIBLIOGRAPHY 47 i v LIST OF ILLUSTRATIONS Page 1.1 A T y p i c a l V i s u a l Data-Computer Interface . . . . . 3 1.2 The New System Interface « 3 1.3a P i c t u r e being Scanned 5 b Video Signal Showing Points where Samples Have been Taken • 5 2.1 The Storage System 8 2.2 The Frequency M u l t i p l i e r 10 2.3a,b,c,d M u l t i p l i e r Waveforms 11 2.4 Pulse A m p l i f i e r . 12 2.5a,b Sample and Hold C i r c u i t s 13 2.6a Sample and Hold Input 14 b Sample and Hold Output 14 2.7 The Display System . 16 2.8 Computer D/A Output 18 2.9 M u l t i v i b r a t o r Delay 19 2.10 Pulse A m p l i f i e r 20 2.11 Gated Operational A m p l i f i e r 21 2.12 Sawtooth Generators 22 3.1 Flow Chart f o r Programme to Store and Display a P i c t u r e at. 4 bits/sample 25 3.2 Flow Chart of Programme to Store a 7-bit Quantization P i c t u r e on PDP-9 Tapes 27 3.3 Flow Chart of Programme to Continuously Display.the 7-bit P i c t u r e 29 v Page 4.1a O r i g i n a l "Test Pattern" P i c t u r e 32 b Output from Computer at 138 usec/sample 32 c Output from Computer at 69 ysec/sample 32 5.1 Phase Locked Loop Scheme 38 5.2 * Generation of a Narrow Pulse 38 v i ACKNOWLEDGEMENT I wish, to express my gratitude to the National Research Council of Canada for the f i n a n c i a l assistance i n carrying out the research and to Dr. Micheal Beddoes f o r very u s e f u l ideas and advice. I would also l i k e to thank Dr. J.S. MacDonald for reading the thesis and making useful suggestions and to Rodney. George, Joan Kushner and Heather DuBois f o r the preparation and typing of the manuscript. v i i 1 1. INTRODUCTION The use of computers to process v i s u a l data has been i n existence f o r some time. The f i r s t problem that researchers i n the f i e l d had to solve was how to get the v i s u a l data information into the computer. This was done by scanning the p i c t u r e on a point-by-point basis i n a TV camera-like manner to obtain an e l e c t r i c a l s i g n a l equivalent of the v i s u a l information. An ordinary TV camera was not used to act as the l i n k between the p i c t u r e and the computer because of the wide bandwidth of the r e s u l t i n g video s i g n a l . This would have caused a data presentation rate greater than the computer could accept. Instead s p e c i a l cameras and display systems were designed to i n t e r f a c e the v i s u a l information to the computer. This thesis presents the re s u l t s of an i n v e s t i g a t i o n i n t o the p o s s i b i l i t y of using an ordinary TV camera and display monitor i n v i s u a l data processing. As a prelude to discussing this and some of the e a r l i e r i n t e r f a c e s , a b r i e f d e s c r i p t i o n of the way a TV p i c t u r e i s obtained w i l l f i r s t be presented. A TV p i c t u r e i s made up of l i n e s which are se q u e n t i a l l y scanned and presented to the viewer. Standard TV presents one l i n e of p i c t u r e i n about 67 usees. A t o t a l of 525 l i n e s are used to complete a p i c t u r e . Just as each p i c t u r e i s made up of l i n e s , each l i n e i s made up of poi n t s . The number of points per l i n e i s determined by the r e s o l u t i o n of the camera. This r e s o l u t i o n varies from about 100 to 650 points per l i n e . Thus a TV p i c t u r e i s made up of points and any system required to store the p i c t u r e information w i l l only need to have the a b i l i t y to store the information of the poi n t s . 1.1 Previous Interface Systems In previous picture-computer i n t e r f a c e systems, the points making up a p i c t u r e were scanned s e q u e n t i a l l y . The rate of scanning was slowed down 2 so that the computer could accept the information. A t y p i c a l system i s shown i n F i g . 1.1 and operates as follows: A transparency of the p i c t u r e i s scanned by a slow moving f l y i n g spot scanner. The resultant e l e c t r i c a l s i g n a l s , representing the brightness of successive p i c t u r e elements are A/D converted and recorded on magnetic tape. This provides a d i g i t a l v ersion of the input p i c t u r e for computer processing. A f t e r the p i c t u r e has been processed according to some algorithms, the computer i n s t r u c t s a microfilm p r i n t e r to generate the new product. This i s done i n a manner which i s the inverse of the o r i g i n a l scanning. A TV-like tube paints the p i c t u r e with a moving spot of l i g h t and a camera records i t on f i l m to provide a photographic end product There are v a r i a t i o n s of t h i s b a s ic method. One such v a r i a t i o n eliminates the need f o r tape recording by i n p u t t i n g the d i g i t a l data s t r a i g h t i n t o the computer memory. In such a case the f l y i n g spot scanner may be required to wait at each p i c t u r e point so as to give the computer s u f f i c i e n t time to accept the data. E i t h e r way the system i s complex and c o s t l y . 1.2 The New Interface System We are here i n t e r e s t e d i n being able to use an ordinary TV camera, scanning at standard speed. Obviously the points on the p i c t u r e cannot be sampled s e q u e n t i a l l y since t h i s rate of presentation i s too f a s t f or any computer. The problem i s overcome t h i s way. A point at the beginning of the p i c t u r e , say, i s sampled and stored i n the computer. Assuming i t takes N Liseconds to store t h i s and a r e s o l u t i o n of 120 p o i n t s / l i n e i s required, at the scanning rate of 67 useconds per l i n e , the time between successive p i c t u r e points i s ^ useconds. Therefore ^57^ points away from the f i r s t point w i l l correspond to a time of N useconds. This i s sampled as the next point for the computer. Another In PUT TRANSPARENCY FLYING--SPOT \ • A/r> CONVERTER DIGITAL TAPE RECOVER COMPUTE^ TAPE RECORDER PICTURE PHOTO&MPHIC EHLfjRGER, MitROFlLN] PRINTER F i g . 1.1 A t y p i c a l Visual Data-Computer Interface, OPVINAR. y PICTURE OR ST/^T/ONSRY OBTEC-T V SYSTEM INTERFACE CofAPOTELR i T>iSPLfiy FROCESSEI) MaNITOR^ gs- PHOTOGRAPH F i g . 1.2 The New System Interface. 4 p o i n t s away, a sample i s . a g a i n t a k e n and t h e v a l u e s t o r e d . The p r o c e s s 67 i s r e p e a t e d u n t i l t h e b o t t o m o f t h e p i c t u r e i s r e a c h e d . When t h e s c a n n e r , ., t . t • 120N . . r e t u r n s t o t h e t o p , a sample i s t a k e n a t a p o x n t t h a t i s ^ p o i n t s away from t h e l a s t one t a k e n a t t h e b o t t o m o f t h e p i c t u r e . As can be seen f r o m F i g u r e 1 . 3 , c o n s e c u t i v e l y numbered p o i n t s , w h i c h r e p r e s e n t a d j a c e n t l y s t o r e d samples i n t h e computer, a r e n o t a d j a c e n t p i c t u r e p o i n t s . T h e r e f o r e , t h e camera must s c a n t h e same p i c t u r e r e p e a t e d l y s e v e r a l hundred t i m e s u n t i l a l l t h e p o i n t s making up t h e p i c t u r e have each been sampled and s t o r e d . The s a m p l i n g i s c o n t r o l l e d s u c h t h a t a l l t h e p o i n t s a r e e a c h sampled o n l y once. I t can be e a s i l y shown by i n d u c t i o n t h a t t h i s c an be done i f a number p i s chosen as t h e number o f p i c t u r e p o i n t s between s u c c e s s i v e samples where p i s n o t a f a c t o r o f and does n o t have a common f a c t o r w i t h t h e t o t a l number o f p i c t u r e p o i n t s , p must a l s o , • 120N be g r e a t e r t h a n . 6 / The i n t e r f a c e s t o r e s t h e d a t a i n t h e computer under programme c o n t r o l . When a l l t h e samples r e p r e s e n t i n g t h e p i c t u r e have been s t o r e d , t h e computer may have t o a r r a n g e them so t h a t a d j a c e n t samples i n s t o r a g e a r e a d j a c e n t p i c t u r e p o i n t s b e f o r e t h e . d a t a , c a n be p r o c e s s e d as d e s i r e d . When t h e d a t a has been p r o c e s s e d and i s re a d y t o be d i s p l a y e d , a r e v e r s e p r o c e s s t o t h e one d e s c r i b e d above now t a k e s p l a c e . The samples must be i n t h e same p o s i t i o n s t h e y were when f i r s t b r o u g h t i n t o t h e computer. The d a t a i s t h e n r e a d o u t i n the same way i t was s t o r e d . The f i r s t i n f o r m a t i o n o u t o f t h e computer goes t o t h e b e g i n n i n g o f t h e s c r e e n d i s p l a y . The s e c o n d sample i s a c t u a l l y "̂32̂  p o i n t s away, so t h e s c r e e n must be b l a n k e d u n t i l b I t h i s p o i n t i s r e a c h e d . When the p o i n t i s r e a c h e d , the s c r e e n i s u n b l a n k e d and the p o i n t d i s p l a y e d . The n e x t sample i s d i s p l a y e d a g a i n "^y^" p o i n t s away f r o m t h e l a s t one. The p r o c e s s goes on u n t i l t he b o t t o m o f t h e s c r e e n i s L I N E 1 _ _ _ LINE 2 LINE 3 LIME -4 /./NE 525 Fig.1.3a P i c t u r e being scanned (0 07) SAMPLING- PULSES F i g . 1.3fc.Video s i g n a l showing p o i n t s where samples have been taken. 6 r e a c h e d . The s c a n n e r r e t u r n s t o the top and d i s p l a y s the n e x t sample a t p o i n t s away f r o m t h e l a s t one a t t h e b o t t o m o f the s c r e e n . These s t e p s a r e r e p e a t e d u n t i l a l l the p o i n t s have been d i s p l a y e d . I f t h e t i m e between samples i s 69 u s e e , a t o t a l t i m e o f about 3.8 seconds w o u l d be r e q u i r e d to b u i l d a p i c t u r e r e p r e s e n t e d by 63,000 p o i n t s . T h i s i s the same time i t t a k e s t o s t o r e t h e p i c t u r e . An o r d i n a r y p h o t o g r a p h i c camera f o c u s e d on t h e d i s p l a y s c r e e n and opened f o r 3.8 seconds w i l l g i v e a p h o t o g r a p h o f t h e p r o c e s s e d v i s u a l i n f o r m a t i o n . A b l o c k d i a g r a m o f the i n t e r f a c e s y s t e m i s shown i n F i g u r e 1.2. Because o f i t s d u a l r o l e the s y s t e m has two p a r t s : a s t o r a g e p a r t and a d i s p l a y p a r t . The s t o r a g e p a r t c o n s i s t s e s s e n t i a l l y o f a sample and h o l d c i r c u i t and c o n t r o l u n i t . The c o n t r o l u n i t d e c i d e s the time a t w h i c h s a m p l i n g o f t h e v i s u a l i n f o r m a t i o n i s t o s t a r t and t h e time between s a m p l e s . I t i s made up o f a f r e q u e n c y m u l t i p l i e r , c o u n t e r and p u l s e s h a p i n g d i g i t a l c i r c u i t s . The d i s p l a y p a r t c o n s i s t s o f a s e t o f m o n o s t a b l e m u l t i v i b r a t o r s , s a w t o o t h g e n e r a t o r s and a g a t e d a m p l i f i e r i n a d d i t i o n t o the c o n t r o l u n i t m e n t i o n e d e a r l i e r . T h i s i n t e r f a c e s y s t e m has s e v e r a l a d v a n t a g e s o v e r some o f t h e e x i s t i n g o n e s . Among t h e s e a r e the a b i l i t y t o use an o r d i n a r y p h o t o g r a p h o r even a s t i l l o b j e c t as t h e v i s u a l i n f o r m a t i o n s o u r c e i n s t e a d o f a t r a n s p a r e n c y , the p o s s i b l i t y o f w o r k i n g w i t h e x i s t i n g o r d i n a r y TV camera and d i s p l a y e q u i p - ment, t h e ease o f v a r y i n g the p i c t u r e r e s o l u t i o n and the low c o s t o f t h e h a r d w a r e . The l i m i t a t i o n s o f t h e s y s t e m and methods f o r i m p r o v i n g i t s p e r - formance w i l l be d i s c u s s e d i n C h a p t e r 5. The n e x t C h a p t e r w i l l be c o n c e r n e d w i t h a d e t a i l e d d e s c r i p t i o n o f the h a r d w a r e w h i l e C h a p t e r 3 w i l l g i v e a r e v i e w o f t h e programming t e c h n i q u e s r e q u i r e d t o o p e r a t e t h e i n t e r f a c e . R e s u l t s o f p e r f o r m a n c e t e s t s on t h e s y s t e m w i l l be p r e s e n t e d i n C h a p t e r 4. / 2. HARDWARE REALISATION 2.1 The Storage System The scheme presented here requires the knowledge of the exact number of points making up a p i c t u r e . Since the manufacturers only give an approxi- mate value with t h e i r cameras, i t i s necessary to f i n d a way of obtaining an exact value. I t i s also necessary to count the points so as to know when to take a sample during storage and when to unblank during display. In order to know the exact number of points making up a p i c t u r e , i t would have to be made up by the designer. The 67 useconds l i n e scanning rate of standard TV camera corresponds to a l i n e frequency of 15.5 Khz i n a 525 l i n e per frame system. There i s an o s c i l l a t o r i n the camera going at t h i s frequency and causing the l i n e scan. I f t h i s frequency i s m u l t i p l i e d by 120, say, an e f f e c t i v e l i n e r e s o l u t i o n of 120 points i s automatically given to the p i c t u r e under observation; each cycle corresponding to a point. A c t u a l l y a TV camera has a master o s c i l l a t o r going at twice the l i n e frequency. In the system described here, a "multiply by s i x t y " c i r c u i t was used to get the desired 120 points per l i n e . The m u l t i p l i e r output was used as a clock to a counter, each clock cycle corresponding to a p i c t u r e point. The counter had a module p-1, so each output of i t corresponded to a point to be sampled on the video s i g n a l . Since the camera w i l l scan the same p i c t u r e repeatedly, i t i s only necessary to keep a count of the number of samples already taken to know when s u f f i c i e n t data has been stored to represent the p i c t u r e completely. This was done by software. The camera also provides a synchronising pulse each time the scanner goes back to the top of the p i c t u r e . I f the computer waits for one of these before s t a r t i n g to store, the f i r s t sample taken w i l l be at the beginning of the p i c t u r e . r MULTIVIBRATOR ' 1 I START OF I S7-otf<?6£ MULTIPLIER ZN-TE&FftCE SYSTEM F i g . 2. .2 The Storage System. 9 A sample and hold c i r c u i t was used to hold a sample long enough f o r the computer to convert the analog s i g n a l into a d i g i t a l value. A c t u a l l y each sample was held u n t i l the next one was taken. The computer w i l l thus have plenty of time to A/D convert and store each sample. The storage part of the i n t e r f a c e i s as shown i n F i g . 2.1. Each of the c i r c u i t s making up the system w i l l now be described b r i e f l y , beginning with the m u l t i p l i e r the diagram of which i s shown i n F i g . 2.2. The b a s i c p r i n c i p l e behind the m u l t i p l i e r i s that of non-linear ampli- f i c a t i o n and f i l t e r i n g . The output of the camera master o s c i l l a t o r i s shown i n F i g . 2.3a. This i s very r i c h i n harmonics. I t was passed through a resonant c i r c u i t of centre frequency 5f where f i s the fundamental. The output of o o the resonant c i r c u i t was used to drive a CE a m p l i f i e r and because of i t s large amplitude, i t caused non-linear a m p l i f i c a t i o n . The output of the a m p l i f i e r i s shown i n F i g . 2.3b. A resonant c i r c u i t tuned to f^=^f^ where f^=5f Q was used to p i c k the fourth harmonic. Thus a m u l t i p l i c a t i o n by 20 was obtained. The new frequency was again n o n - l i n e a r l y amplified to produce another harmonic-rich waveform. A further m u l t i p l i c a t i o n by 3 was obtained by tuning. Since f=2x l i n e frequency, the f i n a l output had a frequency of 120x l i n e frequency. In other words, a system with 120/line r e s o l u t i o n was produced. I f a be t t e r r e s o l u t i o n was required, i t could have been e a s i l y achieved by further m u l t i p l i - c a t i o n and f i l t e r i n g . This method of m u l t i p l i c a t i o n thus allows for a wide range i n the choice of the h o r i z o n t a l r e s o l u t i o n . I t i s i n t e r e s t i n g to note that induc- tors were used i n the resonant c i r c u i t instead of transformers. As long as t h e i r Q's are good enough, inductors work s a t i s f a c t o r i l y i n this type of c i r c u i t . The use of emitter followers between stages i s also to be noted. The output of the m u l t i p l i e r was used as a clock for the counter. F i g . 2 . 2 The Frequency M u l t i p l i e r FIG. 2.3a TV-Camera master o s c i l l a t o r output f » 31KH . 20 u s e c / d i v i s i o n FIG.2.3c M u l t i p l i e r second stage output f = 4x5x31KH = 620KH . z z 5 y s e c / d i v i s i o n FIG. 2.3b M u l t i p l i e r f i r s t stage output f - 5x31KH - 155KH . z z 10 u s e c / d i v i s i o n F I G . 2.3d M u l t i p l i e r t h i r d stage output f - 3x4x5x31KH = 1.86MH . z z 1/2 y s e c / d i v i s i o n -9 v c c 5 £ k • - l O v O U T F i g . Z.4 Pulse A m p l i f i e r The c o u n t e r used i n t h e s y s t e m i s e s s e n t i a l l y t h e p a r a l l e l t y p e d e s c r i b e d i n t h e l i t e r a t u r e . A f t e r a m p l i f i c a t i o n by t h e CE c i r c u i t shown i n F i g . 2.4, t h e c o u n t e r d e c o d e r o u t p u t was used t o sample t h e v i d e o s i g n a l . I n o r d e r t o sample t h e v i d e o s i g n a l a t t h e d e s i r e d t i m e o n l y , a c i r c u i t was r e q u i r e d which, b l o c k s t h e s i g n a l f r o m g o i n g t h r o u g h a t any t i m e o t h e r t h a n when a s a m p l i n g p u l s e i s r e c e i v e d from t h e c o u n t e r . F u r t h e r m o r e ? t h e sample t a k e n a t t h a t t i m e must be h e l d u n t i l t h e n e x t s a m p l i n g p u l s e so t h a t the computer has s u f f i c i e n t t i m e t o A/D c o n v e r t and s t o r e t h e v a l u e . The s a m p l i n g window must n o t be more t h a n about 300ns w i d e i f t h e d e s i r e d h o r i z o n t a l r e s o l u t i o n i s t o be a c h i e v e d . A sample and h o l d c i r c u i t was r e - q u i r e d t o t h e above s p e c i f i c a t i o n s . The b a s i c c i r c u i t f o r a sample and h o l d i s shown i n F i g . 2.5a. The s l e w r a t e o f t h e r e q u i r e d o p e r a t i o n a l a m p l i f i e r i s e x t r e m e l y h i g h and c o u l d n o t be met by t h o s e a v a i l a b l e a t the t i m e t h e i n t e r f a c e was b e i n g d e s i g n e d . A l t e r n a t i v e methods o f sample and h o l d were i n v e s t i g a t e d . I t was found t h a t a s a m p l i n g scope has a sample and h o l d i n i t w i t h t h e f o l l o w i n g c h a r a c t e r i s t i c s : s a m p l i n g window o f 50 n s e c o n d s , J. J F i g . 2.5a Simple Sample WHEH THB SWITCH IS WHEN T H E S W I T C H ; S and Hold C i r c u i t . CtOSEb VOUT ^ V > « S W I T C H SWITCH M E M O R Y PUL$t5 F i g . 2.5b Sampling Scope Sample and Hold block diagram. VJHEN THE SWITCH » S C t O S E i V 0 y T = V,H 14 FIG. 2.6a TV Camera video signal (input to sample & hold) FIG. 2.6b Sample and Hold output hold time up to 500 usee with n e g l i g i b l e decay. I t was designed using valve a m p l i f i e r s . To save time, a s i m i l a r design was not b u i l t , instead a sampling scope "plug-in" unit was used as the sample and hold i n the i n t e r f a c e system. The block diagram of the unit i s shown i n F i g . 2.5b. Normally the scope generates i t s own sampling pulses but i n t h i s system i t was provided with sampling pulses by the counter. The system worked w e l l as can be seen from the pi c t u r e s of F i g . 2.6 which shows the video input and the sample and hold output. The s i g n a l i s now ready f o r input i n t o the computer. 2.2 The Display System When the v i s u a l data has been processed according to the desired algorithms, i t i s required to be read out of the computer and displayed f o r evaluation. The system i n t e r f a c e w i l l act as a l i n k between the computer and a display monitor. I t s operation i n t h i s mode i s the reverse of that described i n the previous se c t i o n . The block diagram f o r the display part of the i n t e r f a c e i s shown i n F i g . 2.7. The m u l t i p l i e r and counter from the storage system are also part of t h i s . In ad d i t i o n , there are 2 sawtooth generators, a gated operational a m p l i f i e r and some m u l t i v i b r a t o r s . The counter output pulses are now used to i n s t r u c t the computer to display the corresponding point on a monitor instead of s t o r i n g . We wish to display the points on the monitor i n the same order that they were stored. The d i g i t a l b i t s i n the computer, representing the samples, were f i r s t D/A converted. Each D/A output was an analog s i g n a l l a s t i n g u n t i l the next sample. The waveform shown i n F i g . 2.8 was obtained from the com- puter. This i s s i m i l a r to the output of the sample and hold, F i g . 2.6b. In order to get point display f o r each analog l e v e l , the l e v e l s were sampled with r ~ FRAME P U L S E S o MyLTivieR/)To« M U L T I P L I E R C O U N T E R . 1 PULSE MULTIVIgfi/^ PULSE r r — 4 LINE puisrs. FRAME ftVLTlVIBRfiTdk PBLfiy SfiVJTooTH GENERATOR X I PROCESSED I V _1 si eiv/rtL. C R T L J F i g 2 . 7 The Display System a narrow pulse by passing them through the gated operational a m p l i f i e r . The gate of the a m p l i f i e r was c o n t r o l l e d by the sampling pulses from the counter. The short duration analog s i g n a l s obtained were then used as the "video" input to the CRT. Since the signals had no synchronizing pulses, unlike a normal composite video s i g n a l from a TV camera, external pulses were provided to cause h o r i z o n t a l and v e r t i c a l d e f l e c t i o n s . These pulses were obtained d i r e c t from the camera. A TV monitor was not a v a i l a b l e during the design and b u i l d i n g of the i n t e r f a c e . The system was therefore designed for display on an ordinary o s c i l l o s c o p e . The amplifiers were used as "plug-ins" to the scope and each a m p l i f i e r had a sawtooth waveform applied to i t . One sawtooth was generated from the h o r i z o n t a l camera d e f l e c t i o n pulses and the other from the v e r t i c a l pulses. There i s usually a few microseconds delay between the time a computer receives the pulse i n s t r u c t i n g i t to output a stored sample and the time the sample i s a c t u a l l y received. Since the i n s t r u c t i n g pulse i s also used to control the gate of the gated operational a m p l i f i e r to allow a converted s i g n a l through, i t was delayed by the few microseconds before being applied to the gate so as to give the computer time to output the value. The v e r t i c a l and h o r i z o n t a l pulses were delayed by the same amount before being applied to the sawtooth generators so as to preserve the r e l a t i v e p o s i t i o n s of the points on the screen. , The exact value of the computer delay i s not known but i s about 5 useconds f o r a PDP-9. A delay of 10 usee was given to each pulse. This gave the computer plenty of time to convert a value and s e t t l e down. The delays were provided by monostable m u l t i v i b r a t o r c i r c u i t s . These c i r c u i t s also acted as shapers of the various pulses. F i g . 2.8 Computer D/A Output F i g . 2.9 M u l t i v i b r a t o r Delay £80 / ^ - W A - IN our 0 OUT F i g . 2.10 Pulse Amplfier The s a w t o o t h waveforms a p p l i e d t o t h e scope c a u s e d a r a s t e r t o appear on t h e s c r e e n . The o u t p u t o f t h e g a t e d o p e r a t i o n a l a m p l i f i e r was a p p l i e d t o t h e CRT b l a n k i n g and th u s z-modulated t h e s c r e e n . The i n t e n s i t y due t o t h e s i g n a l was s u p e r i m p o s e d on t h e r a s t e r . The i n t e n s i t y was t u r n e d down u n t i l t h e r a s t e r d i s a p p e a r e d . The o n l y t h i n g s t h e n v i s i b l e were t h e random p o i n t s t h a t add up t o make t h e p i c t u r e . By t a k i n g a t i m e - e x p o s u r e p h o t o g r a p h o f th e p o i n t s , a p i c t u r e was o b t a i n e d . Most o f t h e components making up t h i s d i s p l a y p a r t o f t h e i n t e r f a c e s y s t e m a r e o f f - t h e - s h e l f I-C modules. The m u l t i v i b r a t o r d e l a y s were made fro m M o t o r o l a MC 799 d u a l v b u f f e r g a t e s . The c i r c u i t f o r one s u c h d e l a y i s shown i n F i g . 2.9. The o n l y e x t e r n a l components a r e r e s i s t o r s and c a p a c i t o r s . The o u t p u t o f t h e f i r s t m u l t i v i b r a t o r was d i f f e r e n t i a t e d . The p o s i t i v e h a l f was t h e n used as i n p u t t o t h e se c o n d m u l t i v i b r a t o r . The w i d t h o f t h e f i r s t p u l s e t h u s d e t e r m i n e d t h e amount o f d e l a y a p p l i e d t o the i n p u t p u l s e . A M o t o r o l a MC 1545 g a t e d o p e r a t i o n a l a m p l i f i e r was used t o o b t a i n t h e n a r r o w a n a l o g s i g n a l s w h i c h z-modulated t h e sc o p e . The a m p l i f i e r works as f o l l o w s . A s i g n a l a p p l i e d t o i t s i n p u t a p p e ars a t t h e o u t p u t i f t h e g a t e 4.7 K O U T + 5 ' F i g . - £••// Gated operational amplifier has 5v o r more a p p l i e d t o i t . I f t h e g a t e v o l t a g e i s l e s s t h a n t h i s t h e i n p u t i s i n h i b i t e d . I n o u r sys t e m t h e g a t e was c o n t r o l l e d by t h e d e l a y e d c o u n t e r o u t p u t p u l s e s . The p u l s e s were f i r s t d i f f e r e n t i a t e d and t h e n a m p l i f i e d by t h e common e m i t t e r c i r c u i t shown i n F i g . 2.10 b e f o r e b e i n g a p p l i e d t o t h e g a t e . The d i f f e r e n t i a t i o n was n e c e s s a r y i n o r d e r t o o b t a i n t h e r e q u i r e d n a rrow a n a l o g s a m p l e s . The c i r c u i t f o r the s a w t o o t h g e n e r a t o r s a r e shown i n F i g . 2.12. They a r e s t a n d a r d s a w t o o t h c i r c u i t s and t h e r e f o r e need no d e s c r i p t i o n . The i n p u t and o u t p u t systems have now been d e s c r i b e d . I n t h e n e x t c h a p t e r t h e s o f t w a r e t h a t c o n t r o l s t h e o p e r a t i o n o f t h e s y s t e m by t h e computer w i l l be d i s c u s s e d . 560- IN 0,1'fuF 2Z0 MPS 637 .00/ 4 70ff -h25v OV7 F i g . Z-f2.°-Hor i z o n t a l Sawtooth Generator OOJ 1— —i i—. %— Fig.z./z'b V e r t i c a l Sawtooth Generator 3. PROGRAMMING TECHNIQUES The philosophy behind the programme that operates with the computer w i l l be presented i n th i s chapter. The systems in t e r f a c e s r e a d i l y with other computers but the actual programme presented here are f o r the PDP-9 machine on which most of the work was done. Any computer that i s to be li n k e d to a TV camera through the i n t e r - face system must have A/D and D/A conversion c a p a b i l i t y , a large core memory or a f a s t mass storage f a c i l i t y . The computer must also be able to sense when to s t a r t s t o r i n g the v i s u a l data and at what rate. Since the sampling speed of the i n t e r f a c e i s geared to the rate of input of data into the computer, a large core memory or a d i s c i n the computer would be i d e a l . When the s i g n a l i s given by the i n t e r f a c e (see F i g . 2.1),' the computer s t a r t s to sample the v i s u a l data. Every sample i s A/D converted and stored i n the memory. Each time a sample i s stored, a count i s taken and when th i s count reaches the number of required samples, sampling ceases. Since consecutive samples stored i n the computer are not consecutive elements on the pi c t u r e being stored, the computer may have to arrange the points so that adjacent samples are adjacent points of the p i c t u r e . The data can then be processed to simulate a desired system (a separate programme i s required to do t h i s ) . A f t e r processing, the samples must be i n the same r e l a t i v e p o s i t i o n s they were when f i r s t brought i n t o the computer. The computer then performs a D/A conversion on the samples and outputs them for display through the i n t e r f a c e system. The computer i s programmed to s t a r t storage or display only when the camera i s at the top of the p i c t u r e scan. With a large core memory v i r t u a l l y any computer can be programmed to carry out the steps described above. A PDP-9 f o r example can have a core memory o f 32,000 w o r d s , each word 18 b i t s l o n g . I f each p i c t u r e sample i s c o n v e r t e d t o 7 b i t s , s a y , f i v e samples can be p a c k e d i n 2 computer words. Thus o n l y 25k words o f memory w o u l d be r e q u i r e d t o s t o r e a c o m p l e t e p i c t u r e o f 525 x 120 i . e . 63,000 p o i n t s . From the memory the d a t a can be s t o r e d on an a u x i l l i a r y s t o r a g e f a c i l i t y f o r l a t e r p r o c e s s i n g . The t y p i c a l t ime f o r A/D c o n v e r s i o n and s t o r a g e o f a sample i s 20 u s e e , t h e r e f o r e t o t a l t i m e t o s t o r e a p i c t u r e w o u l d be about 1.3 s e c o n d s . W i t h a f a s t e r A/D, t h i s t i m e w o u l d be r e d u c e d . 3.1 C o a r s e Q u a n t i z a t i o n More o f t e n t h a n n o t , s m a l l and medium s c a l e computers do n o t have a l a r g e c o r e memory. The PDP-9 u s e d , f o r example had o n l y 16k o f memory. W i t h c o a r s e q u a n t i z a t i o n (4 b i t s / s a m p l e ) , i t was p o s s i b l e to s t o r e the i n f o r m a t i o n o f a p i c t u r e i n t h i s memory. N i n e samples were p a c k e d i n two computer words. Thus o n l y 10.5k words o f the memory were needed f o r t h e 63,000 sam p l e s . The optimum s a m p l i n g speed o f 50Khz c o u l d have been a c h i e v e d . However the i n t e r f a c e s y s t e m was d e s i g n e d f o r o n l y two s a m p l i n g s p e e d s : a p p r o x i m a t e l y 7.25 Khz and 14.5 Khz c o r r e s p o n d i n g t o 253 and 121 p o i n t s r e s p e c t - i v e l y between s a m p l e s . I n t h e case o f 7.25 Khz s a m p l i n g r a t e , about 3.8 seconds a r e r e q u i r e d to s t o r e a c o m p l e t e p i c t u r e as opposed t o t w i c e t h a t f o r 14.5 Khz. The programme f l o w c h a r t e d i n F i g . 3.1 ( a c t u a l programme i s i n c l u d e d i n t h e a p p e n d i x ) was used t o s t o r e the p i c t u r e i n f o r m a t i o n i n t h e computer. When s u f f i c i e n t samples have b e e n s t o r e d i n the memory, t h e d a t a was t r a n s f e r r e d to a t a p e . The computer t h e n went to a subprogramme w h i c h a r r a n g e d the samples as d e s c r i b e d p r e v i o u s l y and p r o c e s s e d them as f o l l o w s : Each sample was com- p a r e d w i t h the one b e f o r e i t . I f the f i r s t t h r e e b i t s were e q u a l , t h e samples were t a k e n as b e i n g o f e q u a l a m p l i t u d e . I f the t h r e e b i t s were u n e q u a l , the v a l u e o f t h e p r e s e n t sample was r e t a i n e d and compared w i t h the n e x t one. S E T UP TAPE TO ITS BEGINNING- f Wfi/T FOrX TOP OF F / C T d * £ POLSE FO/Q, SfiMPLtNG- PUL&E SbmpLE ^ ft /j> CONVERT SHIFT <S- STORE DEPOSIT ON TAPE. ! RETOKN fR0V\ SUBPROGRAM * W/9/T FaP. ToP OF PICTURE PULSE J^ESBT REGISTERS UNPACK j v/ft CONVERT dvTPUT &• SlSPlfly I tV/9/7 FOR, sfimPUNS- PULSE F i g . 3 i Flow c h a r t f o r program t o s t o r e and d i s p l a y a p i c t u r e , h b i t s / s a m p l e . A l l the samples were processed i n this manner. This simple process i s i n f a c t a simulation of a p o s s i b l e d i g i t a l transmission scheme whereby during any par- t i c u l a r sampling period, data i s sent across the communication channel only i f the present sample exceeds the l a s t by a predetermined threshold. A f t e r processing the samples were rearranged, i n preparation for read out and display i n the same order that they were stored. The computer returned to the programme of F i g . 3.1 and s t a r t e d d i s p l a y i n g the processed data. The samples were read out of memory repeatedly so as to provide a continuous display of the p i c t u r e f o r as long as was required. The computer waited for a "top of p i c t u r e " pulse before s t a r t i n g to output and dis p l a y . This ensured the synchronisation of the "video" s i g n a l with the h o r i z o n t a l and v e r t i c a l d e f l e c t i o n s on the screen during the dis p l a y . 3.2 Storage Programme for 7-bit Quantization With a d i s c mass storage f a c i l i t y , no d i f f i c u l t y would a r i s e i n using a 16k system to obtain 7 bits/sample or higher r e s o l u t i o n . A t y p i c a l PDP-9 d i s c takes about 1& usee to trans f e r a word of data to or from memory. It would therefore be p o s s i b l e to operate at the optimum sampling rate of 50 kHz. The PDP-9 used did not have a d i s c , instead i t had a magnetic tape as i t s mass storage f a c i l i t y . The tape has a t r a n s f e r rate of 200 ysec per word (+ 20% depending on the diameter). By packing 5 samples i n 2 computer words i t was possible to store a complete p i c t u r e information on the tape through the memory. The computer can t r a n s f e r data from part of i t s memory on to the tape at the same time as some other data i s being deposited on another part of the memory. At a sampling rate of 7.25 kHz, the time required to f i l l up 2 words i s about 690 ysec. Since only 400 ysec are required to t r a n s f e r 2 words of data to the tape, i t i s p o s s i b l e to overlap the sampling E N T E R I MOVE BOTH TAPES To THE BFG-/MNING- f SET Vp COUNT REGISTERS WAIT FOR TOP OF PICTURE SCfthJ F i g 3»2 Flow chart of program to store a 7-bit quantized picture on PDP-9 tapes. and t r a n s f e r processes. In f a c t the 7.25 kHz sampling rate was chosen during the design of the i n t e r f a c e i n order to be able to do t h i s . Figure 3.2 shows a flow diagram of the programme used to store the 63,000 points p i c t u r e v i s u a l information. Each sample was quantized to 7 b i t s . Five p i c t u r e samples were packed i n 2 computer words. When 8k of memory had been f i l l e d , a tape was set i n motion to s t a r t emptying the memory. Four and h a l f thousand more words of memory were meanwhile being f i l l e d up. By the time this was done, 6k of the memory had been emptied by the tape. The computer went back and s t a r t e d f i l l i n g up the memory again. The tape f i n i s h e d emptying the f i r s t batch before the memory was f i l l e d up a second time. A f t e r the second memory f i l l i n g , the batch of data was w r i t t e n on a second tape. Thus 25k words representing the p i c t u r e were stored on the tapes. I f necessary a separate programme could read the data from the tapes to memory, arrange them as mentioned e a r l i e r and rewrite them on the tapes f o r l a t e r processing. 3.3 The Display Programme The programme shown i n F i g . 3.3 was used to provide a display of the p i c t u r e information stored by the storage programme which deposited,the 25k words on two tapes. The display programme a l t e r n a t e l y read the two stapes into the memory for continuous dis p l a y . The f i r s t tape was read i n t o the memory. The samples i n each word were unpacked and s e q u e n t i a l l y read out and D/A converted when the s i g n a l was given by the i n t e r f a c e . When 8k words had been emptied, the f i r s t tape was set moving back to i t s beginning while more data was read from the second into the memory. By the time a l l the 12.5k o words had been read from tape 2, the f i r s t tape was at i t s beginning and ready to be read again. When 8k words had been emptied from the memory, tape 2 was set i n backward motion and more data read from tape 1. Thus by a l t e r - INTE&KUPT SERVICE ROUTINE E N T E R ' I MOVE TQPES TO y . ser UP COUNT START KEADIH& 12.5 K woRis OF DATA /=KOM T4f>E 1 T» IH7EZRUPT OCCURS IAJHEM /^EAi/M(^ COAlPAETEt) Wr»T FoR. Top of-' PICTURE SCAN UWPflCK SAMPLES, F * O M CsmPPTS-% WORI>S. D/A CON v EAT A.wt> OUTPUT r o INTERFACE SE"F T/)f£ 1 MoViWG- S/)CK . ST/}/?T TAPE Z . THTZRROPT M/IIN p«as«/lM ENTER. STOP T/=)P£" MOTIONS. S E T U^3 TO START REPi2>ltJG- F&OtA ONE TAPE AND OTHER TAPE B / } C K W H E W IH$TKUCTEI> By MAIN PROG-RAM I RETURN TO M/lfA/ pftoCxRAitA r>C-TUR.E HAS BEEN 2\S.f>lfWEb ONCE. ReTUft.N TO TOP To START VISPLfiy 1N G- THE" WfW 12-5 K 8/rrcH OF 2>AT* '4.5 K. 'AVPITIOHPIL DlSPLfiy^i P U W P A C K . MORE W O R - D S ^ O M M E M o f t y ^ 2/SP2/iy T H E P O I N T S F i g 3 - 3 Flow c h a r t of program t o c o n t i n u o u s l y d i s p l a y a p i c t u r e . nately reading from the tapes the v i s u a l data was continuously a v a i l a b l e f o r displa y . S i m i l a r programmes to the : ones described here can be w r i t t e n when other types of computers are involved. However great care i s required i n programming e s p e c i a l l y when tapes are used f o r storage, otherwise synchroni- s a t i o n between the computer data and the camera d e f l e c t i o n pulses may be l o s t f o r much of the time. 4. PERFORMANCE TESTS Q u a l i t a t i v e and q u a n t i t a t i v e tests were performed on the i n t e r f a c e system to check i t s performance as a u s e f u l camera-computer l i n k . The r e s u l t s of these tests are presented here. 4.1 Q u a l i t a t i v e Tests In the q u a l i t a t i v e t e s t s , a TV camera was focused on an object and the output of the camera displayed on an o s c i l l o s c o p e . A photograph of the display i s shown i n F i g . 4.1a (Because of the l i m i t a t i o n s imposed by the scope, a very simple p i c t u r e pattern c o n s i s t i n g of l e t t e r s w r i t t e n on a white background was used as the object ). The video s i g n a l from the TV camera was stored i n the computer using the i n t e r f a c e system and the programme of F i g . 3.1. At a sampling rate of 1 sample about every 138 psec, (about 7.25 kHz), a t o t a l time of about 7.6 seconds was required to store the p i c t u r e . The data i n the computer was arranged and processed by the subprogramme mentioned i n s e c t i o n 3.1. A second subprogramme rearranged the samples a f t e r processing then read them out for display as previously described. A time exposure photograph of the display was taken by opening the p o l a r o i d camera shutter f o r 7.6 seconds. F i g . 4.1b shows the r e s u l t obtained. The r e l a t i v e p o s i t i o n s of the points making up the p i c t u r e were maintained despite the "stroboscope" sampling method. If this was not true the p r i n t e d words would not have come out as they d i d . The v a l i d i t y of the method i s therefore e s t a b l i s h e d . The sampling speed was increased to 1 sample every 69 usee. A t o t a l of about 3.8 seconds was required to store or display the p i c t u r e pattern. A photograph of the scope display i s shown i n F i g . 4.1c. A diagonal scanning pattern i s seen to be superimposed on the p i c t u r e . This a r i s e s as  33 f o l l o w s . The s t r o b o s c o p i c s a m p l i n g scheme r e s u l t s i n a d i a g o n a l p a t t e r n d u r i n g s a m p l i n g and d i s p l a y (see F i g . 1.3). F o r f a s t s a m p l i n g the time t o d i s p l a y a d i a g o n a l i s v e r y s h o r t . Thus i f the p o l a r o i d camera used t o t a k e a p i c t u r e o f t h e p o i n t s i s opened by a few m i l l i s e c o n d s l e s s t h a n t h e e x a c t t i m e r e q u i r e d , some p o i n t s w o u l d be m i s s e d . T h i s w o u l d g i v e r i s e t o the d i a g o n a l p a t t e r n seen i n F i g . 4.1c. F o r s l o w s a m p l i n g t h e t i m e t o d i s p l a y each d i a g o n a l i s l o n g so i n a d v e r t a n t l y s h o r t e n t h e e x p o s u r e t i m e by a few m i l l i s e c o n d s w o u l d n o t impose a n o t i c e a b l e p a t t e r n . The q u a l i t y o f the p i c t u r e s i s due e n t i r e l y t o the scope on w h i c h th e d i s p l a y s were done. T h i s a s s e r t i o n i s b o r n e o u t by t h e p o o r q u a l i t y o f the o r i g i n a l p i c t u r e s ( F i g . 4.1a). N o n - u n i f o r m i l l u m i n a t i o n o f t h e s c r e e n , the v e r y low r e s o l u t i o n o f the scope and t h e n o n - l i n e a r i t y o f the z - a x i s m o d u l a t i o n a r e l a r g e l y r e s p o n s i b l e f o r t h i s . F o u r b i t q u a n t i z a t i o n was used i n the d i s p l a y o f the p r o c e s s e d s i g n a l s . F o r t h e i n p u t p i c t u r e p a t t e r n s u s e d , t h i s q u a n t i z a t i o n l e v e l was q u i t e a d e q u a t e . Any h i g h e r r e s o l u t i o n w o u l d n o t be too m e a n i n g f u l on t h e s c o p e d i s p l a y . However i t i s p o s s i b l e t o q u a n t i z e up to s e v e n b i t s u s i n g t h e programmes d e s c r i b e d i n s e c t i o n s 3.2 and 3.3. The o u t p u t from t h e computer D/A c o n v e r t e r f o r s u c h q u a n t i z a t i o n was p a s s e d t h r o u g h t h e i n t e r f a c e and the c o r r e s p o n d i n g p i c t u r e d i s p l a y e d on t h e s c o p e . W h i l e the s i g n a l i t s e l f l o o k e d l i k e t he sample and h o l d o u t p u t p r e s e n t e d to the computer, d i s p l a y i n g t h e p i c t u r e on t h e sco p e p r e s e n t e d some p r o b l e m . F o r much o f the t i m e , t h e r e was l o s s o f s y n c h r o n i s a t i o n , as a r e s u l t the p i c t u r e was s p l i t up, p a r t . o f i . i t a p p e a r i n g on one s i d e o f the sco p e and the r e s t on t h e o t h e r s i d e . T h i s l o s s o f s y n c h r o n i s a t i o n was due t o t h e few m i l l i s e c o n d s l o s t by t h e computer i r i . s t a r t i n g and t u r n i n g the t a p e s a r o u n d . The p r o b l e m was s o l v e d by making the computer check f o r "top of p i c t u r e " p u l s e a f t e r each c o m p l e t e p i c t u r e d i s p l a y . I f synchronization was .lo s t , i t would be re-established before the display began 'again. 4.2 Quantitive Test The i n t e r f a c e was tested f o r noise and j i t t e r . The most l i k e l y source of noise i n the system would be the sample and hold. The unit i s supposed to sample the input video s i g n a l and hold the analog s i g n a l u n t i l the next sample. I f another sample i s taken before the output a m p l i f i e r s e t t l e s down, j i t t e r i n g w i l l r e s u l t . This j i t t e r e f f e c t was tested for i n the following manner. The camera was focused on a white sheet of paper and the s i g n a l due to this stored on tape through the memory using the program of F i g . 3.2. The 63,000 7-bit samples were then compared (by the computer) with each other to see how many samples have d i f f e r e n t values from the r e s t . I t was found that only 100 samples were d i f f e r e n t . T h i r t y nine of these samples were out by 2 b i t s , the re s t by only 1 b i t . 5. SUMMARY AND CONCLUSIONS A s y s t e m has been p r e s e n t e d w h i c h can be used as a l i n k i n P i c t u r e P r o c e s s i n g by Computer. The i n t e r f a c e makes i t p o s s i b l e to use o r d i n a r y TV camera and d i s p l a y m o n i t o r i n such p r o c e s s e s i n s t e a d o f b u i l d i n g s p e c i a l o n e s . R e s u l t s were p r e s e n t e d t o p r o v e t h e v a l i d i t y o f t h e method. The advantage o f the s y s t e m o v e r p r e v i o u s i n t e r f a c e s were a l s o p r e s e n t e d . The l i m i t a t i o n s o f the i n t e r f a c e w i l l be d i s c u s s e d h e r e as w e l l as methods o f i m p r o v i n g the s y s t e m t o imp r o v e i t s r e l i a b i l i t y . Some o f the uses t h a t t h e i n t e r f a c e may be p u t t o w i l l a l s o be b r i e f l y m e n t i o n e d . 5.1 L i m i t a t i o n s Because o f t h e arrangement t h a t may be n e c e s s a r y b e f o r e a v i s u a l d a t a s t o r e d i n the computer u s i n g t h i s i n t e r f a c e can be p r o c e s s e d , i t i s n o t p o s s i b l e t o use t h e i n t e r f a c e as a l i n k f o r r e a l time o n - l i n e computer p i c t u r e p r o c e s s i n g . F o r t h e same r e a s o n i t i s n o t p o s s i b l e to p r o c e s s a p o r t i o n o f t h e p i c t u r e and d i s p l a y i t i n d e p e n d e n t l y o f the r e s t o f the p i c t u r e . I f a p o r t i o n o f the v i s u a l d a t a i s p r o c e s s e d , the whole p i c t u r e w i l l have t o be d i s p l a y e d i n o r d e r t o be a b l e to o b s e r v e t h e e f f e c t o f the p r o c e s s i n g on the p o r t i o n o f i n t e r e s t . F o r some o p e r a t i o n s t h e s e l i m i t a t i o n s may make the i n t e r - f a c e s y s t e m u n a c c e p t a b l e . An example o f t h i s i s c o n t o u r t r a c i n g i n p a t t e r n r e c o g n i t i o n computer p r o c e s s i n g . Where t h i s l i m i t a t i o n i s n o t i m p o r t a n t , t h e r e i s a n o t h e r p r o b l e m t h a t may a r i s e . T h i s i s the f a c t t h a t a c o n t i n u o u s d i s p l a y o f t h e p r o c e s s e d d a t a f o r a l o n g p e r i o d o f ti m e may n o t be p o s s i b l e on computers w i t h s m a l l o r s l o w s t o r a g e f a c i l i t y . T h i s i s b e c a u s e o f t h e l o s s o f s y n c h r o n i s a t i o n m e n t i o n e d i n S e c t i o n 4.1. F o r example t h e t a p e t u r n around t i m e on a PDP-12 i s so l o n g as t o p r e c l u d e t h e two tape s t o r a g e and d i s p l a y method d e s c r i b e d i n C h a p t e r 3. The b e s t t h a t can be done on a PDP-12 t h a t has o n l y m a g n e t i c t a p e f o r mass s t o r a g e i s t o s t o r e t h e v i s u a l i n f o r - m a t i o n s e v e r a l t i m e s on t h e t a p e . The tape has a - c a p a c i t y o f about 1.6 m i l l i o n b i t s . T h i s can s t o r e f o u r 63,000 sample p i c t u r e i n f o r m a t i o n i f each sample i s q u a n t i z e d t o 6 b i t s . By s t o r i n g the same p i c t u r e on the tape f o u r t i m e s , i t w i l l be p o s s i b l e t o g e t t h e p r o c e s s e d i n f o r m a t i o n d i s p l a y e d f o u r t i m e s c o n t i n u o u s l y . A f t e r t h a t ^ the t a p e has t o r e w i n d b a c k to i t s b e g i n n i n g ( a b o u t 30 s econds a r e r e q u i r e d f o r t h i s ) b e f o r e t h e d i s p l a y can be r e s t a r t e d . T h i s may n o t be a s e r i o u s l i m i t a t i o n i f a l l t h a t i s r e q u i r e d i s f o r t h e d i s p l a y to l a s t l o n g enough f o r a p h o t o g r a p h t o be t a k e n . A n o t h e r p r o b l e m t h a t may a r i s e w i t h the i n t e r f a c e s y s t e m i s t h e l i m i t o f v a r i a t i o n o f t h e v e r t i c a l r e s o l u t i o n . The 525 l i n e s / p i c t u r e o f t h e TV camera i s t h e maximum r e s o l u t i o n p o s s i b l e . T h i s s h o u l d n o t be a s e r i o u s drawback however s i n c e f o r most a p p l i c a t i o n s t h i s r e s o l u t i o n i s q u i t e ade- q u a t e . The l o w e r r e s o l u t i o n s e a s i l y o b t a i n e d a r e l i m i t e d t o s u c h n e a r s u b m u l t i p l e s of 525 as 263 and 131. These a r e o b t a i n e d by u s i n g the i n t e r l a c e f a c i l i t y i n the camera. F o r i n s t a n c e , to o b t a i n 263 l i n e s / p i c t u r e , the computer i s programmed t o s t o r e the samples f r o m e v e r y o t h e r f i e l d o n l y . These t h e n a r e the l i m i t a t i o n s o f t h i s i n t e r f a c e s y s t e m , i n s p i t e o f them i t s h o u l d s t i l l be u s e f u l as a v i s u a l d a t a - c o m p u t e r l i n k . 5.2 Methods o f Improvement The p h i l o s o p h y b e h i n d t h e d e s i g n o f t h e i n t e r f a c e i s t h a t ,the s a m p l i n g p u l s e s be l o c k e d ( i e w e l l s y n c h r o n i s e d ) w i t h t h e d e f l e c t i o n p u l s e s g e n e r a t e d by t h e camera. I f t h i s i s n o t so t h e n i t i s q u i t e p o s s i b l e t h a t t h e samples t a k e n d u r i n g t h e s t o r a g e of t h e v i s u a l d a t a w i l l n o t be d i s p l a y e d i n t h e i r r e l a t i v e p o s i t i o n s a f t e r p r o c e s s i n g . I n a d d i t i o n some samples may be m i s s e d a l t o g e t h e r . The use of the m u l t i p l i e r - d i v i d e r scheme i s t o a v o i d t h i s p r o b l e m . I f t h e m u l t i p l i e r i s w e l l d e s i g n e d , t h e p r o b l e m i s n o t s e r i o u s . However even a m u l t i p l i e r o f the b e s t d e s i g n may sometime b u r s t i n t o o s c i l l a t i o n i n d e p e n d e n t l y o f t h e camera m a s t e r o s c i l l a t o r and s y n c h r o n i s a t i o n may be l o s t f o r a t i m e . An a l t e r n a t i v e and more s t a b l e way t o l o c k the s a m p l i n g p u l s e s t o the d e f l e c t i o n p u l s e s w o u l d be t o use the p h a s e - l o c k e d l o o p method. I n t h i s method, a waveform i s g e n e r a t e d by a c r y s t a l o s c i l l a t o r a t t h e r e q u i r e d h i g h f r e q u e n c y , e.g. 1.85 MHz o f t h e p r o t o t y p e . T h i s f r e q u e n c y i s t h e n d i v i d e d down by d i g i t a l c o u n t e r s (a v e r y much s i m p l e r o p e r a t i o n t h a n m u l t i p l y i n g ) to t h e d e f l e c t i o n f r e q u e n c y . The camera d e f l e c t i o n f r e q u e n c y i s compared w i t h t h e e x t e r n a l l y g e n e r a t e d one and t h e e r r o r s i g n a l i s u s e d t o c o n t r o l t h e f r e q u e n c y o f t h e c r y s t a l o s c i l l a t o r i n a f e e d b a c k c o n t r o l l o o p method. F i g . 5.1 shows t h i s d i a g r a m m a t i c a l l y . I f e i t h e r t h e camera o r the o s c i l l a t o r d r i f t s f rom the p r e s c r i b e d f r e q u e n c y , t h e o t h e r f o l l o w s a u t o m a t i c a l l y and the s a m p l i n g p u l s e s w i l l be p e r m a n e n t l y l o c k e d to t h e d e f l e c t i o n p u l s e s . I t was m e n t i o n e d i n S e c t i o n 2.2 t h a t t h e s a m p l i n g p u l s e s must be v e r y n a rrow so t h a t t h e d e s i r e d h o r i z o n t a l r e s o l u t i o n may be a c h i e v e d . The n a r r o w p u l s e s were g e n e r a t e d by u s i n g d i f f e r e n t i a t o r s . F o r t h e low r e s o l u t i o n o f 120 p o i n t s / l i n e , t h i s was q u i t e a d e q u a t e . F o r h i g h e r r e s o l u t i o n s however where s a m p l i n g p u l s e s o f 50ns o r l e s s a r e r e q u i r e d a l t e r n a t i v e methods may be n e c e s s a r y . One s i m p l e way o f o b t a i n i n g a v e r y n a r r o w p u l s e i s shown i n F i g . 5.2. The d u r a t i o n o f t h e p u l s e i s g i v e n by the d e l a y of t h e l o g i c g a t e . F o r a TTL g a t e f o r i n s t a n c e t h i s d e l a y i s u n d e r 10 n s . The p r o t o t y p e s y s t e m was d e s i g n e d t o have 2 s a m p l i n g s p e e d s , 69 y s e c / s a m p l e and 138 y s e c / s a m p l e . I t i s q u i t e easy t o have s e v e r a l s a m p l i n g speeds by s i m p l y h a v i n g s e v e r a l c o u n t d e c o d e r s i n s t e a d o f two. As can be CflMERFf f : £ — PULSES f F i g . 5.1 P h a s e l o c k e d l o o p s c h e m e T T — ^ T J O U T F i g . 5.2 G e n e r a t i o n o f a narrov/- p u l s e . seen from the photographs i n Chapter 4 however a high sampling rate tends to superimpose an unacceptable sampling pattern on the p i c t u r e . I t would be better to f i n d the f a s t e s t sampling rate at which the sampling pattern : disappears and use th i s i n a f i n a l design. In the l a s t few months, I.C and d i s c r e t e component a m p l i f i e r s of required c h a r a c t e r i s t i c s to b u i l d a sample and hold to the following s p e c i f i c a t i o n s have become a v a i l a b l e : sampling window 50 ns, hold time up to 1 usee. I t was mentioned i n the i n t r o d u c t i o n that the sample and hold i n the i n t e r f a c e would be required to hold a sample u n t i l the next sample i s taken. This i s a r i g i d s p e c i f i c a t i o n which i s not r e a l l y necessary. The computer A/D converter needs the signal -'to be a v a i l a b l e f o r l e s s than 1 usee. Therefore a sample and hold with the s p e c i f i c a t i o n s mentioned above w i l l be quite adequate. With these modifications i t should be p o s s i b l e to b u i l d a completely r e l i a b l e system. Some of the uses to which such a system can be put w i l l be described i n the next s e c t i o n . 5.3 P o s s i b l e Uses The f i e l d of TV bandwidth compression was one of the f i r s t areas of p i c t u r e processing where computers were applied. A pi c t u r e would be stored i n the computer, the v i s u a l data would then be processed according to some algorithms so as to simulate various schemes proposed f o r reducing TV bandwidth. The processed data would be read out and displayed to see what e f f e c t the simulation has had on the q u a l i t y of the p i c t u r e . The i n t e r f a c e system described i n t h i s thesis can be used as the l i n k between the p i c t u r e information and the computer. Some of the processing f o r the simulation of TV bandwidth compression however require adjacent samples i n the computer to correspond to consecutive p i c t u r e points. This i s - t h e r e f o r e an area where arrangement of data a f t e r storage would be required. While a l o t of work i s s t i l l being done on TV bandwidth compression, much att e n t i o n i s now being paid to the r e l a t i v e l y newer area of image processing by computer, pattern recognition. This t i t l e covers a wide area i n c l u d i n g such diverse topics as f i n g e r p r i n t i d e n t i f i c a t i o n , spacecraft image evaluation and biomedical image processing. The one thing these have i n common i s that the computer i s usually only required to recognize c e r t a i n c h a r a c t e r i s t i c s of the pi c t u r e information stored i n i t . Display of the processed data i s very seldom required. Thus i n the case of f i n g e r p r i n t i d e n t i f i c a t i o n f o r example, several f i n g e r p r i n t p i c t u r e information are entered into the computer, the computer i s required to compare them and f i n d which two are i d e n t i c a l . Weather forecasting by computer i s another f i e l d of pattern recognition. The processing required to be done by the computer i s s i m i l a r to the one j u s t described. S a t e l l i t e weather photographs are fed into the computer, information i s then extracted from t h i s to p r e d i c t the weather. Since i n these and many other areas of pattern r e c o g n i t i o n there i s no necessity f o r disp l a y i n g the processed information, the i n t e r f a c e system should be more r e a d i l y acceptable as a l i n k between the photographic information and the computer. This i s because the possible loss of syn- chronization during the display that was mentioned i n Section 4.1 w i l l not a r i s e . . T I T L E STORE MO. 1 (STORED .GLOBL BACK /THIS PROGRAM STORES A TV PICTURE ON TAPE THROUGH MEMORY. /EACH SAMPLE IS CONVERTED TO 11 BITS 7 0F WHICH ARE MOT /USED. 9 SAMPLES ARE PACKED IN 2 WORDS. AFTER STORING, THE /COMPUTER GOES TO ANOTHER PROGRAM TO MAKE USE OF THE DATA. / / SKPFRFr705301 CLRFRF=705302 SKPSAF=705401 C L R S A F r 7 0 5 4 0 2 SKPADF :705601 CLRADF=705602 CLRBUF :701104 LRS 1 1 = 640511 ADRB=701117 ADSC=701304 ALS3=640703 ALS7=643707 L R S D 6 4 0 5 0 1 ' • ' ' LRS7=640507 LRS5=640505 DTLA=707545 DTDF:707601 DTXA=707544 DAL 1 = 703 107 GO JMP START /THIS PART OF THE PROGRAM SETS OVER LAC (CBLK /UP THE TAPE TO ITS BEGINNING. DAC* (31 DZM* (30 . LAC (221000 DTLA WAIT DTDF JMP . - 1 SEARCH LAC RBLK CMA TAD (1 TAD CBLK SMA JMP REV DAC* (30 LAC (010000 DTXA JMP WAIT REV SZA JMP INVT LAC (020000 DTXA JMP START INVT CMA TAD (1 DAC* (30 LAC (050000 DTXA JMP WAIT /THE STORING OF THE PICTURE IN /MEMORY BEGINS HERE. THE INPUT /SIGNAL IS SAMPLED AND A/D CONVERTED. /NEGATIVE SAMPLES ARE IGNORED SINCE. /THEY ONLY REPRESENT THE SYNC PART /OF THE ORIGINAL VIDEO SIGNAL. / / / START CLRBUF CLRADF LAC (163S DAC* (13 LAC ( - 1 5 5 3 0 . DAC COUNT* ' CLRFRF CLRSAF SKPFRF JMP . - 1 • SKPSAF JMP . - I ADSC SKPADF JMP . - 1 CLRFRF CLRSAF DZM TEMP# CLA JMS SAMPLE JMP SI 0 ADD TEMP DAC TEMP ADRB SKPSAF JMP . - 1 ADSC DAC HOLD# AND (004000 SAD (004000 JMP IGNORE LAC HOLD CMA TAD (1 DAL I LAC HOLD CLRSAF JMP * SAMPLE IGNORE DZM HOLD JMP LOOP / / / / / / SAMPLE LOOP / 'TOP OF PICTURE ° PULSE PRESENT? ./NO. TEST AGAIN / Y E S . WAIT FOR PRESENCE OF SAMPLING /PULSE THEN START SAMPLING AND /A/D CONVERTING. . - /SAMPLING PULSE PRESENT? /NO. TEST AGAIN /YES . SAMPLE AND A/D CONVERT / /THIS PART OF THE PROGRAM WILL MASK /OUT THE LAST 7 BITS OF EACH CONVERTED /SAMPLE AND PACK 9 SAMPLES IN 2 WORDS. / / 51 ALS7 AND (740300 JMS SAMPLE 52 ALS3 AMD (036000 JMS SAMPLE 53 LRS1 AND (001700 JMS SAMPLE 54 LRS5 AND (000074 JMS SAMPLE . - . 55 LRS11 , AND (000003 ADD TEMP DAC* 10 LAC HOLD LRS7 AMD (000003 . DZM TEMP JMS SAMPLE 56 ALS7 AND (740000 JMS SAMPLE 57 ALS3 AND (036300 JMS SAMPLE 58 LRS1 AND (001700 JMS SAMPLE 59 LRS5 AND (000074 ADD TEMP DAC* 10 1SZ COUNT * JMP .+2 JMS* BACK / / / / / / / / / CLA DZM TEMP ' JMS SAMPLE JMP SI /SUFFICIENT SAMPLES TAKEN? /NO. GO AND TAKE MORE /YES . GO TO SUBROUTINE TO /TRANSFER DATA TO TAPE /SUBROUTINE TO DEPOSIT DATA ON TAPE . /THE DAT IS STORED ON TAPE SO THAT /IT CAN BE PROCESSED LATER. / / WRITE LAC ( - 2 DAC* (30 • - • . LAC (CBLK DAC* (31 ; LAC (231300 DTLA DTDF JMP . - 1 . LAC CBLK • • . • DAC SAVE# . LAC (1636 DAC* (31 LAC ( - 1 5 5 3 0 DAC* (30 LAC (005000 DTXA DTDF JMP . - 1 LAC (020000 DTXA JMS* BACK /EXIT TO ANOTHER PROGRAM. RBLK I CBLK 0 .END GO . T I T L E D I S P L A Y .NO. 1 ( D S P L Y 1 ) .GLOBL BACK / T H I S PROGRAM P R O V I D E S A D I S P L A Y OF A T V P I C T U R E , /STORED IN MEMORY BY T H E P R E V I O U S PROGRAM, ON AN / O S C I L L O S C O P E . T H E S A M P L E S R E P R E S E N T I N G THE P I C T U R E /ARE U N P A C K E D , D/A C O N V E R T E D AND P R E S E N T E D TO T H E / I N T E R F A C E S Y S T E M . / • / / S K P F R F = 7 0 5 3 8 1 C L R F R F : 7 0 5 3 3 2 S K P S A F = 7 0 5 4 3 1 • C L R S A F : 7 0 5 4 3 2 A L S 1 1 : 6 4 0 7 1 1 A L S 1 : 6 4 0 7 0 1 -A L S 5 : 6 4 0 7 0 5 A L S 7 : 6 4 0 7 0 7 L R S 3 : 6 4 0 5 0 3 L R S 7 : 6 4 0 5 0 7 DAL 1 : 7 0 3 1 0 7 D T L A : 7 0 7 5 4 5 D T D F : 7 3 7 6 0 1 . D T X A : 7 0 7 5 4 4 / S E T UP FOR T H E D I S P L A Y T A K E S P L A C E H E R E . T H E COMPUTER /WAITS FOR A 'TOP OF P I C T U R E ' P U L S E B E F O R E S T A R T I N G TO /OUTPUT TH E D A T A . / / BACK 0 AWAY L A C ( - 1 5 5 3 0 DAC COUNT* L A C ( 1 6 3 6 D A C * ( 1 0 P L A C E L A C * 10 DAC T E M P * L R S 7 AND ( 0 0 3 6 0 0 CM A TAD (1 L A C ( J M P D l DAC P L A C E C L R F R F C L R S A F S K P F R F JMP .-2 S K P S A F JMP .-1 DAL 1 L A C (-3 TAD (1 S Z A JMP .-2 C L R S A F L A C TEMP JMP D2 /THE U N P A C K I N G AND D I S P L A Y / I N T H I S S U B R O U T I N E . / / P R O C E S S T A K E P L A C E D S P L Y 0 AND ( 0 0 3 6 0 0 CMA TAD (1 S K P S A F JMP .-1 DAL 1 L A C (-2 TAD (1 S Z A JMP .-2 C L R S A F L A C TEMP J M P * D S P L Y D l L A C * 10 DAC TEMP L R S 7 JMS D S P L Y D2 L R S 3 JMS D S P L Y D3 A L S 1 JMS D S P L Y DA A L S 5 JMS D S P L Y D5 A L S 1 1 AND ( 0 0 3 0 0 0 DAC K E E P # L A C * 10 DAC TEMP A L S 7 AND ( 0 0 0 6 0 0 TAD K E E P JMS D S P L Y D6 L R S 7 JMS D S P L Y D.7. L R S 3 . JMS D S P L Y D8 A L S 1 JMS D S P L Y D9 A L S 5 JMS D S P L Y I S Z COUNT JMP D l , JMP AWAY / D I S P L A Y P U L S E P R E S E N T ? /NO. T E S T A G A I N / Y E S . D I S P L A Y THE C O R R E S P O N D I N G / S A M P L E . / A L L S A M P L E S D I S P L A Y E D ? /NO. GO AND D I S P L A Y R E M A I N D E R . / Y E S . GO BACK TO T H E TOP AND / S T A R T D I S P L A Y I N G T H E P I C T U R E / A G A I N . .END BACK BIBLIOGRAPHY 1. W.F. Schreiber and D.N. Graham, "A D i g i t a l Scanner f o r Computer Image Processing". Indian I n s t i t u t e of Technology, Dept. of E.E., A p r i l 1966. 2. A z r i e l Rosenfeld, "P i c t u r e Processing by Computer". New York Academic Press, 1969. 3. L.D. Harmon and K.C. Knowlton, "Picture Processing by Computer". Science Vo l . 164, pp. 19-29, A p r i l 1969. 4. Tektronix, Inc., "Sampling Notes". Beaverton, Oregon, 1969. 5. Louis Nashelsky, " D i g i t a l Computer Theory". New York, John Wiley & Sons Inc., 1966. 6. O.J. Tratiak, The "SCAD", M.I.T. Research Lab of E l e c t r o n i c s . Quarterly Progress Report 83, Oct. 15, 1966. 7. T.S. Huang and O.J. Tretiak, "Research i n Pi c t u r e Processing" i n o p t i c a l and E l e c t r o - O p t i c a l Information Processing. Chapter 3, M.I.T. Press, 1965. 8. H.U. Malmstadt and C.G. Enke, " D i g i t a l E l e c t r o n i c s f o r S c i e n t i s t s " , New York, W.A. Benjamin Inc., 1969. 9. S p e c i a l Issue on "Redundancy Reduction", Proceedings of the IEEE V o l . 55, March 1967. 10. J.G. Cossalter, "A Computer Visual-Input System f o r the Automatic Recognition of Blood C e l l s " , M.A.Sc. Thesis, U.B.C, August 1970. 11. E. Renschler and B. Welling, "An Integrated C i r c u i t Phase-Locked Loop D i g i t a l Frequency Synthesizer". A p p l i c a t i o n Note AN-463. Motorola Semiconductor Products. Inc.

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