[robski]

Thanks Mick - Is there any part which is proving troublesome which maybe I can expand upon or provide diagrams ?

Below is an example set of Quantization tables used in a Nikon Camera. The upper 8 x 8 matrix is used for the luminance channel and the lower two are used for the two chrominance channels. From this we can see that the tables used for the chrominance channels discard more of the high frequencies than the luminance table.

The whole point of the DCT is to separate the image data into bands of frequencies. Then through the Quality Control setting (compression level slider) the high frequencies components can be progressively discarded as the compression level (ratio) is increased.

The 64 quantized frequency bands are then sorted so that the order runs from the lowest frequency component to the highest. Which will result in an increasing stream of zeros at the end as the compression is increased. It then becomes idea to apply the lossless Run length compression method on the long stream of zeros in the next stage.