Compression is used to reduce file sizes and change various attributes of an image file. These attributes include:
Compression can be lossy or lossless. Lossless compression means that as the file size is compressed, the picture quality remains the same - it does not get worse. Also, the file can be decompressed to its original quality. Lossy compression permanently removes data.
There are a number of types of compressed image file. These include the following.
PNG is a lossless compression type. It is often used where the graphic might be changed by another person or where the image contains layers of graphics that need to be kept separate from each other. It is high quality.
JPEG is often used for digital camera images because it has a fairly small file size for the quality that it displays. JPEG is a lossy format that offers a higher compression rate than PNG in the trade-off for quality.
GIF compresses images to a maximum 8-bit colour depth, making it unsuitable for high-quality photographs. GIF is often used where transparency is needed on the graphic. GIF can also be used to store simple animated images.