Overall, this article is a pretty good overview of how lossy image/video compression works. However, what the author describes as "quantization" is actually a l

Overall, this article is a pretty good overview of how lossy image/video compression works. However, what the author describes as "quantization" is actually a low pass filter. With quantization, you do not simply zero out the high frequency components. You "snap" them to specific intervals. For example, if you have some data varying between 0 and 100, like [7, 39, 97, 42, 13], quantizing that by a factor of 5 would give you [5, 40, 95, 40, 15]. This gives you an approximation of the fine details, rather than simply throwing them away.