DCT is also often used as a substep in more complex image (or video) compression algorithms. That is, first identify some sub-area of the image with a lot of de

DCT is also often used as a substep in more complex image (or video) compression algorithms. That is, first identify some sub-area of the image with a lot of detail, then apply DCT to that sub-area and keep more of the spectrum, then do the same for other areas and keep more or less of the spectrum. This is where the quantization parameters that you have seen for video compression algorithms affect the behavior.