Image compression is a type of data compression applied to digital images, to reduce their cost for storage or transmission.

Image compression may be lossy or lossless.

Lossless compression is a class of data compression algorithms that allows the original data to be perfectly reconstructed from the compressed data.

Lossless data compression is used in many applications. For example, it is used in the ZIP file format.

Lossless compression is used in cases where it is important that the original and the decompressed data be identical, or where deviations from the original data would be unfavorable.

Typical examples are executable programs, text documents, and source code. Some image file formats, like PNG or GIF, use only lossless compression, while others like TIFF and MNG may use either lossless or lossy methods.

Lossy compression methods, especially when used at low bit rates, introduce compression artifacts. Lossy methods are especially suitable for natural images such as photographs in applications where minor (sometimes imperceptible) loss of fidelity is acceptable to achieve a substantial reduction in bit rate.

Lossy compression that produces negligible differences may be called visually lossless.

Methods for lossless image compression are:

• Run-length encoding
• Predictive Coding
• Entropy encoding
• Adaptive dictionary algorithms such as LZW

Methods for lossy compression:

• IGS
• Transform coding
• JPEG
• Vector Quantization