![]() ![]() And I think Alex has given a pretty good explanation. That's an interesting point you raise Ted, one which I haven't thought about before. The quality factor controls the number of approximations used. This can save space by storing colour approximations for your pixels. ![]() This feeds into the algorithm used to group similar colours together and refer to them with a master colour table. In that case you adjust the quality factor for the JPEG. In the end I would not worry about it and choose RGB unless file size is really important. This saves a lot of space and I think is used in TV broadcasting. Use 8-bit for the Y and only 4-bit for the chroma. One advantage of YCrCb is that you can use a lower bit depth for the chroma channels since the eye is less sensitive to this. Effectively you would be getting 3:1 compression which is much higher than 4:2:2 (3:2) or 4:2:0 (2:1). However I haven't seen software that saves images using a Bayer mosaic. The image could be reconstructed by a routine demosaicing process. A better pattern for sampling would be the familiar 2 green and 1 red and 1 blue Bayer filter array. You cannot sub-sample RGB using a similar pattern and get a nice image since it would be like having 4 red values but only 2 blue and 2 green for 4 pixels. But with video you have 25-30 frames per second and so averaging over the frames and your eyes filling in details makes it less noticeable. It is usually most apparent on boundaries of block colour more like you see in text rather than natural images. If you use 4:2:2 sampling then you will get a smaller image but with slightly worse colour rendition. The numbers refer to the sampling width, the number of chroma samples on the first row and the number of samples on the second row. If you use 4:4:4 then you are not compressing anything and it will be just the same quality as using RGB. It is less common to use the compression for JPEG although it is supported in the standard. However the compression options are most often used with MPEG files for video. This still renders an image that is recognisable but uses less space. ![]() Essentially you keep more information in the brightness channel (Y) and less in the two chroma channels. YCrCb colour space is used for the advantages of image compression. ![]()
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