Chroma Subsampling - Effectiveness

Effectiveness

While chroma subsampling can easily reduce the size of an uncompressed image by 50% with minimal loss of quality, the final effect on the size of a compressed image is considerably less. This is because image compression algorithms also remove redundant chroma information. In fact, by applying something as rudimentary as chroma subsampling prior to compression, information is removed from the image that could be used by the compression algorithm to produce a higher quality result with no increase in size. For example, with wavelet compression methods, better results are obtained by dropping the highest frequency chroma layer inside the compression algorithm than by applying chroma subsampling prior to compression. This is because wavelet compression operates by repeatedly using wavelets as high and low pass filters to separate frequency bands in an image, and the wavelets do a better job than chroma subsampling does.