Image compression

Image compression reduces the data needed to store or transmit an image, either by removing redundancy or by discarding information judged less important.

Lossless compression: A data-compression method that reconstructs the original input exactly after decompression. It reduces image data without changing any pixel values.
JPEG: A family of image coding standards commonly used for lossy compression of continuous-tone images. Its transform-based coding made compact photographic images practical across devices and networks.
Rate–distortion theory: A framework that studies the minimum data rate needed to represent a source at a specified distortion level. It formalizes the tradeoff between compressed image size and reconstruction quality.
Digital image: An image represented as discrete samples, commonly arranged as pixels with numerical values. Compression operates on the sampled values and structure of digital images.
Image file format: A specification for organizing and encoding image data in a file. Compression methods are packaged within formats that determine compatibility and supported features.
Lossy compression: A data-compression method that discards information so the decoded output differs from the original. It achieves smaller images by accepting some reconstruction error.
PNG: A raster image format that uses lossless compression and supports transparency. It preserves exact image data for graphics, text, and screenshots.
Compression artifact: A visible distortion introduced by a lossy encoding or decoding process. Blocking, ringing, and other artifacts reveal what image compression sacrifices.
Pixel: A sample representing color or brightness at a location in a digital image. Pixel values are the basic data units that image codecs transform or encode.
Progressive JPEG: A JPEG coding mode that displays an image in successive scans of increasing detail. It lets a compressed image become recognizable before all its data arrives.

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