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Improvements of demosaicking and compression for single sensor digital cameras Doutre, Colin Ray

Abstract

Most consumer digital cameras captured colour images using a single light sensor and a colour filter array (CFA). This results in a mosaic image being captured, where at each pixel location either a red, green, or blue sample is obtained. The two missing colours at each location must be interpolated from the surrounding samples in a process known as demosaicking. In most current digital cameras, demosaicking is carried out in RGB colour space and later the image or video is converted to YCbCr 4:2:0 format and compressed with standard methods. Most previous research on demosaicking and compression in digital cameras has addressed the issues separately. That is, current demosaicking methods ignore the fact that the data will later be compressed, and compression techniques ignore the fact that the data was captured with a CFA. In this thesis we proposed two methods for optimizing the demosaicking and compression processes in digital cameras. First we propose a fast demosaicking method that directly produces an image in YCbCr 4:2:0 format (the colour format most commonly used in compression). This reduces the computational complexity relative to the conventional approach of performing demosaicking in the RGB space and later converting to YCbCr 4:2:0 format. Second, we propose two methods for compressing video captured with a CFA prior to demosaicking being performed. This allows us to take advantage of the smaller input data size, since demosaicking expands the number of samples by a factor of three. Our first CFA video compression method uses standard H.264, while our second method uses a modified motion compensation scheme that further increases compression efficiency by exploiting the properties of CFA data.

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