Compression Types
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| Baseline JPEG |
| Other names |
Discrete Cosine Transform, DCT, JPEG |
| Identifier(s) |
PUID:
x-cmp/11
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| Family |
|
| Description |
The JPEG compression algorithm was developed in 1990 by the Joint Photographic Experts Group of ISO and CCITT, for the transmission of colour and greyscale images. It is a lossy technique which provides best compression rates with complex 24-bit (True Colour) images. It achieves its effect by discarding image data which is imperceptible to the human eye, using a technique called Discrete Cosine Transform (DCT). It then applies Huffman encoding to achieve further compression. The JPEG specification allows users to set the degree of compression, using an abstract Quality Setting. This provides a trade-off between compression rate and image quality. It is important to note that the Quality Setting is not an absolute value, with different JPEG encoders use different scales, and that even the maximum quality setting for baseline JPEG involves some loss. JPEG compression is most commonly used in the JPEG File Interchange Format (JFIF), SPIFF and TIFF. |
| Lossiness |
Lossy |
| Released |
01 Jan 1994 |
| Withdrawn |
|
| Developed by |
 International Standards Organisation
|
| Supported by |
|
| Documentation |
ISO/IEC 10918-1: 1994, Information technology - Digital compression and coding of continuous-tone still images: Requirements and guidelines |
| Rights |
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| Note |
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|
| Lempel-Ziv-Welch |
| Other names |
LZW |
| Identifier(s) |
PUID:
x-cmp/12
|
| Family |
|
| Description |
The Lempel-Ziv-Welch compression algorithm was developed by Terry Welch in 1984, as a modification of the LZ78 compressor. It is a lossless technique which can be applied to almost any type of data, but is most commonly used for image compression. LZW compression is effective on images with colour depths from 1-bit (monochrome) to 24-bit (True Colour). LZW compression is encountered in a range of common graphics file formats, including TIFF and GIF. |
| Lossiness |
Lossless |
| Released |
01 Jan 1984 |
| Withdrawn |
|
| Developed by |
T A Welch / [No organisation specified]
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| Supported by |
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| Documentation |
Welch, T A, 1984, A technique for high performance data compression, IEEE Computer, 17: 6 |
| Rights |
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| Note |
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|
| Run Length Encoding |
| Other names |
RLE |
| Identifier(s) |
PUID:
x-cmp/13
|
| Family |
|
| Description |
Run length encoding (RLE) is perhaps the simplest image compression technique in common use. RLE algorithms are lossless, and work by searching for runs of bits, bytes, or pixels of the same value, and encoding the length and value of the run. As such, RLE achieves best results with images containing large areas of contiguous colour, and especially monochrome images. Complex colour images, such as photographs, do not compress well – in some cases, RLE can actually increase the file size. There are a number of RLE variants in common use, which are encountered in the TIFF, PCX and BMP graphics formats. |
| Lossiness |
Lossless |
| Released |
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| Withdrawn |
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| Developed by |
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| Supported by |
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| Documentation |
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| Rights |
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| Note |
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|
| CCITT T.4 |
| Other names |
CCITT Group 3 |
| Identifier(s) |
PUID:
x-cmp/14
|
| Family |
|
| Description |
Officially known as CCITT T.4, Group 3 is a compression algorithm developed by the International Telegraph and Telephone Consultative Committee in 1985 for encoding and compressing 1-bit (monochrome) image data. Its primary use has been in fax transmission, and it is optimised for scanned printed or handwritten documents. Group 3 is a lossless algorithm, of which two forms exist: one-dimensional (which is a modified version of Huffman encoding) and two-dimensional, which offers superior compression rates. Due to its origin as a data transmission protocol, Group 3 encoding incorporates error detection codes. Group 3 compression is most commonly used in the TIFF file format. |
| Lossiness |
Lossless |
| Released |
01 Jan 1985 |
| Withdrawn |
|
| Developed by |
International Telecommunication Union
|
| Supported by |
|
| Documentation |
CCITT Blue Book, 1989, Volume VII, Fascicle VII.3: Terminal equipment and protocols for telematic services, recommendations T.0 - T.63 |
| Rights |
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| Note |
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|
| CCITT T.6 |
| Other names |
CCITT Group 4 |
| Identifier(s) |
PUID:
x-cmp/15
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| Family |
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| Description |
Officially known as CCITT T.6, Group 4 is a compression algorithm developed by the International Telegraph and Telephone Consultative Committee as a development of the two-dimensional Group 3 standard for encoding and compressing 1-bit (monochrome) image data. It is faster, and offers compression rates which are typically double those of Group 3. Like Group 3, it is lossless and designed for 1-bit images. However, being designed as a storage rather than transmission format, it does not incorporate the error detection and correction functions of Group 3 compression. Group 4 compression is most commonly used in the TIFF file format. |
| Lossiness |
Lossless |
| Released |
01 Jan 1989 |
| Withdrawn |
|
| Developed by |
International Telecommunication Union
|
| Supported by |
|
| Documentation |
CCITT Blue Book, 1989, Volume VII, Fascicle VII.3: Terminal equipment and protocols for telematic services, recommendations T.0 - T.63 |
| Rights |
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| Note |
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Details: File format summary
: detailed report on file format 
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