Why don't we just use an hash function to reduce the size of an bitmap,rgb raw image?isn't it more efficient of storage data and it produces lossless image after being decoded?The decoder is also very simple and they would use an universal standard hash code for all images,some private image would have its own hash code.It's an opportunity for us to compress a file to very low capacity without any complicated algorithm and entropy code?
Unlike a compression function, which can be reversed to recover (an approximation to) the original data, a hash function is irreversible. You can hash your image, and the hash is a lot smaller than the original image, but you can't get the original image back from the hash.
A hash function is useful for cases where there are only a small number of possible images, which everyone knows about. An example use-case might be something like Telegram or WhatsApp stickers, where there's a fixed set of images, and centrally assigning ID numbers causes distributed systems problems.