Compression schemes are used to re-encode data into more compact representations of the same information. Works best for flat color, sharp-edged art. Horizontal bands of color compress better than vertical bands. Worse results for flat color and sharp-edge images. PNGs compress both horizontally and vertically, so solid blocks of color generally compress best.
Image compression can be either lossy and lossless.
Lossy compression creates smaller files by discarding some information from the original image. It removes details that are supposedly too small for the human eye to differentiate. Lossless compression, on the other hand, never removes any information from the original file. JPEG uses lossy compression . GIF and PNG files, on the other hand, use lossless compression .