Graphics Interchange Format

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1357 hex GIF87a / GIF89a

GIF ( Auspr. by inventor [ d͡ʒɪf ], but usually [ gɪf ] ) for Graphics Interchange Format (English Graphics Interchange Format ) is a graphics format with good lossless compression for images with low color depth (up to 256 ( = 28 ) different colors per frame). In addition, several individual images can be saved in a file that is interpreted by suitable viewing programs such as web browsers as animations. One no longer commonly used another name of the format is GIFF ( Graphics Interchange File Format).

History

The GIF was developed by Steve Wilhite was introduced in 1987 from the U.S. online service CompuServe for the color format to replace the previously used RLE format, which could only display black and white images. GIF became popular mainly because of its efficient, LZW compression. The image files required significantly less disk space than other time of the usual graphics formats such as PCX or MacPaint. Even large images could be transmitted in a reasonable time, even with slow modems. In addition, the open licensing policy of CompuServe made it possible for any programmer to implement GIF for your applications free of charge, provided that attached a copyright notice of the online service.

When the Internet age began, GIF was next to the black and white image format XBM the second standard format for images. The now dominant JPEG format became common only after the introduction of the Mosaic browser. While the XBM format was completely displaced to GIF could claim because - unlike JPEG - transparency and animations allowed.

The first in 1987 brought out version of GIF was the version " 87a ". In 1989, CompuServe published an expanded version, called " 89a ". You can see the version in the first six bytes of a GIF file. These correspond to either the ASCII character GIF87a GIF89a or.

In the 2010s GIF animations experienced a surprising comeback on the Web. The reason the popularity of photos forums pages is like tumblr and 4chan called, where they are used to, among other things Create Cinema autographs and stereograms.

In 2012, the word " GIF " was officially recognized as a noun and verb in the English language, " to create a GIF " as a verb with the meaning. The U.S. branch of the Oxford University Press chose it as the word of the year, since GIF: " have developed into a tool with serious applications in journalism and research."

Properties

Colors, transparency and image size

In GIF color information in a color table (also called color palette ) is stored. These can contain up to 256 different items that are free from 2563 ≈ 16.7 million possible color values ​​selected. When the image format was introduced, this was not a significant limitation, since hardware with which you could display more colors, because of the very high cost was not widespread. For simple drawings, black-and- white photographs and the like 256 colors or gray levels are still generally sufficient today. More complex images, such as color photos or drawings with extensive color gradients must therefore be reduced before storage to 256 colors or less ( color quantization ). The resulting color levels or dither effects are disturbingly visible, especially with large images.

From GIF89a a color entry in the palette can be defined as transparent. This can be at any location shine through the respective background color and eg give the impression that the image would have a non-rectangular shape. Partial transparency ( alpha transparency ) as in PNG, but is not possible: a pixel can only be either " fully visible " or " completely transparent ".

The maximum size of GIF images is 65,535 × 65,535 pixels, or about 4294 megapixels.

GIF has the MIME type image / gif or image / giff.

Interlacing

Since the typical range of online connectivity of a web user already integrated in the late 1980s, early 90s was still very limited, was in GIF87a the possibility of so-called interlaced display. The picture data are not stored in order, but at first, each line 8 ( top to bottom ), then every fourth, every second, and finally the remaining. When displaying the graphics in the web browser these lines are then displayed in first 8 times, then 4 times, finally double height until all data are loaded and the image is 1:1. In this way, the viewer has a rough preview, which is then refined with increasing amount of data, even at very slow connection still relatively fast. An improved method ( Adam7 ) was adopted for the PNG format.

Images with more than 256 colors

Already GIF87a allows multiple frames, each of which has its own color palette ( Local Color Table) may have to be stored in a file. This option can be used to true-color images ( true color GIFs) to save. Unlike the animated GIFs they will not be played in sequence but constructed side by side. For this purpose, the whole picture like a chess board ( tile graphics ) is divided into frames with no more than 256 colors, each have its own palette. Thus, for images with 24-bit color depth save lossless and standards compliant in GIF and represent. Since the individual images are compressed independently and also each requiring an uncompressed local color range 6-768 bytes in length, is usually to achieve in such " true-color GIFs " overall not a good compression rate more.

True -color GIFs can for example be generate with PhotoImpact or free under the GPL ANGIF - Library by Phil Howard. Konqueror, Safari and Netscape Communicator 4.7x, they show immediately and correctly. However, Irfanview, Firefox, Internet Explorer and Opera show the individual frames with mandatory breaks of about 100 ms between them on, so until full screen layout of the sense of animation can be created. True -color GIFs can be easily as a 24- bit RGB images in the graphics program GIMP but not import to export. The image viewer XnView shows severe graphical glitches, the image is not visible. The image display of Windows XP only reports an error and does not display the image. The programs reggae and SView5 show the files easily.

Photoshop can any versions of GIF show both edit and save.

Another technique to be able to represent real- color images of GIF introduced by GIF89a transparency: it can be a GIF file to be constructed as a series of overlapping images each with its own 256- color table in which the underlying parts of the image on transparent single - pixel the overlying be visible.

True-color GIFs have so far reached no great awareness and dissemination, possibly because most of the GIF decoder in image viewers and browsers conform with the specification interpret a delay value of 0 ms between the single frame of GIFs typically 100 ms, although the specification explicitly prohibits this:

"8 The decoder. The decoder Has the Following primary responsibilities. - Process each graphic in the Data Stream in sequence, without delays other than Those specified in the control information. [ ... ] "

Animations

Can be the ability of GIF to store a plurality of individual pictures, and use for storing animation. An official description of the format used does not exist, but it has established itself as a de facto standard among browser vendors. The individual images are played sequentially delayed by the web browser or image editing program. By this way, the transmission of short animation, film-like files was possible for the first time. Therefore Animated GIFs reached a large spread and are still in use.

GIF allows animations that constantly repeat themselves (see globe right) or animations that occur only once or a few times, and then stand on the last frame stay (see lunar impact left).

GIF and LZW patents

Discovered in 1994 the software company Unisys that she held a 1983 filed a software patent on the LZW method used in GIF and then demanded royalties from CompuServe. The two companies agreed that CompuServe receives a license from Unisys, which may then be passed on to producers of commercial programs that use GIF,. CompuServe demanded for a fee of one dollar, and 1.5 % of the sale of the Software, and at least 15 cents per copy sold. The validity of this license also limited to programs that worked with the CompuServe online service.

Later, the LZW algorithm could also be licensed directly from Unisys. At this point, GIF was already so prevalent on the World Wide Web that few manufacturers could resist the demands of Unisys. Although free software and non-commercial products were initially exempt even from the Unisys license claims, this led to the development of PNG.

In 1999, Unisys, now that royalties would be payable even for free software. At the same time you went legal action against individual users who were using GIF images on their websites, which were produced by unlicensed software.

U.S. patent expired on 20 June 2003; in the United Kingdom, France, Germany and Italy was the patent until June 18, 2004 in Japan until 20 June 2004 and Canada until 7 July 2004.

In addition, the company IBM was granted a patent on the same method; this is due to a failure of the U.S. Patent Office. Login was indeed three weeks before the Unisys; under the patent laws of the United States, however, this does not mean that the IBM patent is a priority. Rather, the IBM patent due to the previously granted Unisys patent should be invalid. It was due to expire on 11 August 2006.

According to the Software Freedom Law Center ran on 1 October 2006, the last essential patents on the use of GIFs, so that a free use is now possible. To expiration of the patent commented a deputy Unisys:

" We have not Evaluated the new recommendation for PNG, and it remains to be seen Whether the new version will have an effect on the use of GIF images. If so, the patent situation will have Achieved its purpose, Which is to advance technological innovation. So we applaud that. "

"We have the new [ W3C ] recommendation for PNG not assessed, and it remains to be seen whether the new version will have an impact on the use of GIF images. If so, then the patent situation will have served their purpose, namely to promote technical innovation. Therefore, we welcome that "

Comparison with modern standards

The unpatented PNG format is specifically designed to replace GIF as the format for still images on the World Wide Web. PNG offers more features, almost always a better compression per frame and can display more colors than GIF. The latter is the biggest advantage of PNG over GIF.

However, PNG GIF could wear nothing despite the royalties for the LZW method for a long time, because it's on the LZW method were up to the expiry of the patent almost only individuals, their GIFs replaced as protest against the Unisys licensing policies by PNG images. Companies paid rather because the PNG format has not been properly or not supported by most browsers. In addition, PNG - unlike GIF - present animations. Only since most web browsers support the PNG format, increases its use. By now ( mid-2009 ) was able to PNG through its technical advantages replace the outdated GIF many areas (except for animations).

Developed to PNG MNG animation format could not prevail to this day. That's why a PNG extension called APNG was proposed by Mozilla, which may also represent animations in addition to pictures and thus can be regarded as a complete GIF replacement. Advantage over MNG is that browsers and general software without the support of APNG ( such as Internet Explorer) animations in this format show at least the first image. However APNG was not accepted by the PNG Group as a PNG extension 2007. Nevertheless Mozilla APNG developed further, for example, published in June 2008 versions of Firefox (3.0) and Opera ( 9:50 ) APNG support, but no more MSG.

Partly as a replacement for GIF animations on the websites of major companies and organizations, Adobe Flash has been established. Exceed the possibilities offered by Flash can GIF by far, in addition to graphics and photos, among other things (dynamic ) animations and movies are played back with sound; However, this must be installed an additional Flash Player.

Although GIF can be regarded as technically outdated, but it is due to its wide distribution, its popularity and the applicability has so far not completely replaced for animations.

Dissemination and use

GIF images were soon put to greater use after the introduction as a web format, eg of programs such as computer games, DOS or databases. In the early days of the Web photos and other true-color graphics were mostly stored in GIF, although it actually technically ill-suited. The time not yet very widespread True Color graphics were thereby reduced (usually by the use of dithering) to 256 colors or less. GIFs in this application are therefore still commonly found on the few sites since that time still ( almost ) exist unchanged. For photographs and other applications which require large color depths and as a general purpose image format GIF was unusual since the 2000s.

However, GIF images are still ( despite competition from PNG) used in large numbers on the Internet, especially for banners, smaller images and animations. GIF animations ( for example, rotating or flashing text elements ) were at the beginning of the popularity of the WWW, often used before the year 2000 as a focal point and as a first dynamic multimedia elements on many otherwise static web pages ( which earned them even the jocular nickname " Fidgety GIF " ). Although technically outdated experienced in the 2010s GIF animations another comeback on the Web and are used for example to create Cinema grams or stereograms. The reason the popularity of photos forums pages is called as tumblr and 4chan. Another reason is the wide band and good technical support for animated GIFs on all browsers and operating system boundaries, as opposed to technically more modern alternatives such as SVG, Flash or animated PNGs which often need additional codecs or plugins.

Format Comparison for true-color image

256-color GIF ( 1160 × 1376 pixels, 955 KB)

True color PNG 1160 × 1376 pixels, 2.25 MB)

Real color GIF with 50,490 colors (250 × 296 pixels, 304 KB)