image compression it has been suggested that this article be merged with intraframe coding discuss proposed since october 2018 image compression is a type of data compression applied to digital images to reduce their cost for storage or transmission algorithms may take advantage of visual perception and the statistical properties of image data to provide superior results compared with generic compression methods comparison of jpeg images saved by adobe photoshop at different quality levels and with or without save for web lossy and lossless image compression image compression may be lossy or lossless lossless compression is preferred for archival purposes and often for medical imaging technical drawings clip art or comics 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 runlength encoding used in default method in pcx and as one of possible in bmp tga tiff area image compression dpcm and predictive coding entropy encoding adaptive dictionary algorithms such as lzw used in gif and tiff deflate used in png mng and tiff chain codes methods for lossy compression reducing the color space to the most common colors in the image the selected colors are specified in the colour palette in the header of the compressed image each pixel just references the index of a color in the color palette this method can be combined with dithering to avoid posterization chroma subsampling this takes advantage of the fact that the human eye perceives spatial changes of brightness more sharply than those of color by averaging or dropping some of the chrominance information in the image transform coding this is the most commonly used method in particular a fourierrelated transform such as the discrete cosine transform dct is widely used n ahmed t natarajan and krrao discrete cosine transform ieee trans computers 9093 jan 1974 the dct is sometimes referred to as dctii in the context of a family of discrete cosine transforms eg see discrete cosine transform the more recently developed wavelet transform is also used extensively followed by quantization and entropy coding fractal compression other properties the best image quality at a given compression rate or bit rate is the main goal of image compression however there are other important properties of image compression schemes scalability generally refers to a quality reduction achieved by manipulation of the bitstream or file without decompression and recompression other names for scalability are progressive coding or embedded bitstreams despite its contrary nature scalability also may be found in lossless codecs usually in form of coarsetofine pixel scans scalability is especially useful for previewing images while downloading them eg in a web browser or for providing variable quality access to eg databases there are several types of scalability quality progressive or layer progressive the bitstream successively refines the reconstructed image resolution progressive first encode a lower image resolution then encode the difference to higher resolutions component progressive first encode greyscale version then adding full color region of interest coding certain parts of the image are encoded with higher quality than others this may be combined with scalability encode these parts first others later meta information compressed data may contain information about the image which may be used to categorize search or browse images such information may include color and texture statistics small preview images and author or copyright information processing power compression algorithms require different amounts of processing power to encode and decode some high compression algorithms require high processing power the quality of a compression method often is measured by the peak signaltonoise ratio it measures the amount of noise introduced through a lossy compression of the image however the subjective judgment of the viewer also is regarded as an important measure perhaps being the most important measure notes and references image compression lecture from mit opencourseware image coding fundamentals a study about image compression with basics comparing different compression methods like jpeg2000 jpeg and jpeg xr hd photo data compression basics includes comparison of png jpeg and jpeg2000 formats faqwhat is the state of the art in lossless image compression from compcompression iprg an open group related to image processing research resources vtedata compression methodslosslessentropy type unary arithmetic asymmetric numeral systems golomb huffman adaptive canonical modified range shannon shannonfano shannonfanoelias tunstall universal expgolomb fibonacci gamma levenshtein dictionary type byte pair encoding deflate snappy lempelziv lz77 lz78 lz1 lz2 lzfse lzjb lzma lzo lzrw lzs lzss lzw lzwl lzx lz4 brotli zstandard other types bwt ctw delta dmc mtf paq ppm rle audioconcepts bit rate average abr constant cbr variable vbr companding convolution dynamic range latency nyquistshannon theorem sampling sound quality speech coding subband coding codec parts alaw law acelp adpcm celp dpcm fourier transform lpc lar lsp mdct psychoacoustic model wlpc imageconcepts chroma subsampling coding tree unit color space compression artifact image resolution macroblock pixel psnr quantization standard test image methods chain code dct ezw fractal klt lp rle spiht wavelet videoconcepts bit rate average abr constant cbr variable vbr display resolution frame frame rate frame types interlace video characteristics video quality codec parts lapped transform dct deblocking filter motion compensation theory entropy kolmogorov complexity lossy quantization ratedistortion redundancy timeline of information theory compression formats compression software codecs vtemultimedia compression and container formatsvideocompressionisoiec mjpeg motion jpeg 2000 mpeg1 mpeg2 part 2 mpeg4 part 2asp part 10avc mpegh part 2hevc itut h120 h261 h262 h263 h264 h265 dv vvc smpte vc1 vc2 vc3 vc5 aomedia av1 ietf vp8 sac avs others apple video bink cinepak daala dvi ffv1 huffyuv indeo lagarith microsoft video 1 msu lossless oms video pixlet prores 422 prores 4444 quicktime animation graphics realvideo rtvideo sheervideo smacker sorenson video spark theora thor vp3 vp6 vp7 vp9 wmv xeb yuls xvc audiocompressionisoiec mpeg1 layer iii mp3 mpeg1 layer ii multichannel mpeg1 layer i aac heaac aacld mpeg surround mpeg4 als mpeg4 sls mpeg4 dst mpeg4 hvxc mpeg4 celp mpegd usac mpegh 3d audio itut g711 alaw law g718 g719 g722 g7221 g7222 g723 g7231 g726 g728 g729 g7291 ietf opus ilbc speex vorbis 3gpp amr amrwb amrwb evrc evrcb evs gsmhr gsmfr gsmefr etsi ac3 ac4 dts sac avs dra others acelp alac asao atrac celt codec2 flac isac monkeys audio tta true audio mt9 musepack optimfrog osq qcelp rcelp realaudio rtaudio sd2 shn silk siren smv svopc twinvq vmrwb vselp wavpack wma mqa aptx ldac imagecompressioniec isoitut w3c ietf ccitt group 4 gif heif hevc jbig jbig2 jpeg jpegls jpeg 2000 jpeg xr jpeg xt png tiff tiffep tiffit others apng bpg djvu exr flif icer mng pgf qtvr wbmp webp containersisoiec mpeges mpegpes mpegps mpegts iso base media file format mpeg4 part 14 mp4 motion jpeg 2000 mpeg21 part 9 mpeg media transport itut h2220 t802 ietf rtp ogg smpte gxf mxf 3gpp 3gp and 3g2 others amv asf aiff avi au bpg bink smacker bmp divx media format evo flash video iff m2ts matroska webm quicktime file format ratdvd realmedia riff wav mod and tod vob ifo and bup collaborations netvc mpegla see compression methods for methods and compression software for codecs 