Image compression is an encoding process aiming to reduce the size of images. Compressed images require less storage space when saved to disk, and less RAM when handled in memory (although they must be decompressed for displaying).
Each codec implements a specific compression algorithm. Some implement lossless compression: once compressed with a lossless codec, an image can be reconstructed from its compressed form without loss of quality.
In favor of better storage savings, however, most codecs slightly change certain image pixels to further reduce size. Doing so results to loss of image information. Lossy codecs carefully choose which pixels to alter and how, taking into account the human perception of visual images: pixels are altered in such ways that fool the human eye into perceiving the image as being identical to the original, while the compressed image will take up much less space on disk and on the network.
|QPx_CompressPicture||Compress a picture variable|
|QPx_GetCompressedPictureInfo||Get information about a compressed picture (legacy or new)|