[canistel]

Sorry to ask a very ametuerish question, but how is lossless compression of an image different from regular run of the mill compression (zip, 7z)? Is there any sort of underlying pattern or feature which is unique to image data that is leveraged/exploited for lossless image compression?

[artificialidiot]

Yes. If you examine PNG format, it actually uses pixels around a pixel to predict its value and compress the difference, which is much closer to 0 values. It actually uses zlib to compress just like gzip.