Compressione JPEG  Compressão JPEG JPEG-Komprimierung Compression JPEG Compresión JPEG

JPEG compression

The acronym JPEG (Joint Photographic Expert Group comes from the meeting held in 1982 of a group of photographic experts, whose main concern was to work on the ways to transmit information (still or animated images). In 1986, the ITU-T developed compression methods intended for fax sending. These two groups joined to create a joint photographic experts group (JPEG).

Unlike LZW compression, JPEG compression is a lossy, , which affords it one of the best compression ratios, despite the slight loss of quality (20: 1 with 25:1 without any significant loss of quality).
This compression method is much more effective for photographic images (comprising many different coloured pixels) than on geometrical images (unlike LZW compression) because the nuance differences due to compression are very visible in the latter.

The stages of JPEG compression are the following:

  • Chrominance re-sampling, because the eye cannot distinguish chrominance differences within a square of 2x2 points
  • • Image division into blocks of 8x8 points, then the application of the DCT function (Discrete Cosine Transform, which breaks up the image into a sum of frequencies
  • Quantification of each block, i.e., a loss coefficient is applied (which makes it possible to determine the size/quality ratio) which will “cancel out” or decrease high frequency values, in order to attenuate the details by intelligently going over the block with RLE coding (in a zigzag pattern in order to remove as many zero values as possible).
  • • Image encoding then compression using the Huffman method

File formats that save a flow coded in JPEG are actually called JFIF (JPEG File Interchange Format), but the term is usually deformed into “JPEG file".

It should be noted that there is a lossless form of JPEG coding. Although little used by the data-processing community in general, it is used especially for the transmission of medical images in order to avoid confusing artefacts (purely dependent on the image and its digitalization) with real pathological signs. Compression is thus much less effective (only factor 2).

Last update on Thursday October 16, 2008 02:43:16 PM.This document entitled « JPEG compression » from Kioskea (en.kioskea.net) is made available under the Creative Commons license. You can copy, modify copies of this page, under the conditions stipulated by the licence, as this note appears clearly.

Best answers for « JPEG compression » in :
RLE Compression Show Pixel packing Pixel packing is a method which allows pixels to be stored in an optimal way: for a monochrome image there are, by definition, only two colours, a point of the image can thus be coded in only one bit to gain memory space. RLE...
LZW Compression Show LZW compression Abraham Lempel and Jakob Ziv are the creators of the LZ77 compressor, invented in 1977 (hence its name). This compressor was then used for filing (ZIP, ARJ and LHA formats use it). In 1978 they created the LZ78 compressor...
[Myth] A Jpeg file can contain a virus ShowA Jpeg file can contain a virus? Myth Truth Links Myth A Jpeg file can contain a virus. Truth A JPEG is a file can get infected. However, in order to activate the virus, the file must be run. As the JPEG file is an image file, it will...
Reducing a Jpg image size ShowReducing a Jpg image size Step 1 (optional!): Skip GREYCstoration on the image Step 2: Reduce the resolution Step 3: Lower quality Step 4: Remove unnecessary information Conclusion If you find that your JPEG files are too large...
Compress / decompress a ZIP FILE ShowCompress / decompress a ZIP FILE ZIP files are specifically used under Microsoft Windows. Under Linux, the compression format is GZip (.Gz) format or Tarball(.Tar.gz). You can compress and decompress ZIP files with zip / unzip,...
Download Free Word/Doc Txt to Image Jpg/Jpeg Bmp Tiff Png ShowIt is usually the images that we insert into Word, Excel or PowerPoint documents. This time, it is the opposite, because we are going to convert these documents to image formats. All to Jpg / JPEG Image Bmp Tiff Png Converter is a powerful tool which...
Download JpegGuard JPEG Image Protection ShowJpegGuard has been designed for the users who would like to protect their image files. It allows to encrypt all the files which have JPG and JPEG formats on your computer. It begins scanning the hard disk entirely (or a selected folder) before...
Download JPEG Saver ShowJPEG SAVER is a screen saver which allows to display the images and photos of your choice. Features: - to place images at random on the screen at random and enlarge them in order to adapt them to the screen. - numerous transition effects - to...
MP3 ShowIntroduction to the MP3 format MP3 ("MPEG Audio layer 3") is a lossy audio data compression format, developed by the International Organization for Standardization (ISO). This format is used to compress normal audio formats (WAV or CD audio) at a...
Video compression (codecs) ShowThe concept of codec A non-compressed video image occupies approximately 1 MB. In order to obtain a fluid video, it is necessary to have a frequency of at least 25 or 30 images per second, which produces a data flow of approximately 30 MB/s, that...
Data compression ShowWhy compress data? Nowadays, the computing power of processors increases more quickly than storage capacities, and is much faster than network band-widths, because this requires enormous changes in the telecommunication infrastructures. Thus, to...