GIF - Knowledge

2000:#0 | 000h Initialize root table of 9-bit codes palette | : colors | : #255 | 0FFh clr | 100h end | 101h | 100h Clear Pixel Local | color Palette string | BLACK #40 28 | 028h 1st pixel always to output WHITE #255 FF | String found in table 28 FF | 102h Always add 1st string to table FF | Initialize local string WHITE #255 FF FF | String not found in table | 0FFh - output code for previous string FF FF | 103h - add latest string to table FF | - initialize local string WHITE #255 FF FF | String found in table BLACK #40 FF FF 28 | String not found in table | 103h - output code for previous string FF FF 28 | 104h - add latest string to table 28 | - initialize local string WHITE #255 28 FF | String found in table WHITE #255 28 FF FF | String not found in table | 102h - output code for previous string 28 FF FF | 105h - add latest string to table FF | - initialize local string WHITE #255 FF FF | String found in table WHITE #255 FF FF FF | String not found in table | 103h - output code for previous string FF FF FF | 106h - add latest string to table FF | - initialize local string WHITE #255 FF FF | String found in table WHITE #255 FF FF FF | String found in table WHITE #255 FF FF FF FF | String not found in table | 106h - output code for previous string FF FF FF FF| 107h - add latest string to table FF | - initialize local string WHITE #255 FF FF | String found in table WHITE #255 FF FF FF | String found in table WHITE #255 FF FF FF FF | String found in table No more pixels 107h - output code for last string 101h End 1077:, have been developed to approximate a wider range of colors with a small color palette by using pixels of two or more colors to approximate in-between colors. These techniques sacrifice spatial resolution to approximate deeper color resolution. While not part of the GIF specification, dithering can be used in images subsequently encoded as GIF images. This is often not an ideal solution for GIF images, both because the loss of spatial resolution typically makes an image look fuzzy on the screen, and because the dithering patterns often interfere with the compressibility of the image data, working against GIF's main purpose. 657: 617: 3769: 2622: 568: 2645:. Each frame in an animation GIF is introduced by its own GCE specifying the time delay to wait after the frame is drawn. Global information at the start of the file applies by default to all frames. The data is stream-oriented, so the file offset of the start of each GCE depends on the length of preceding data. Within each frame the LZW-coded image data is arranged in sub-blocks of up to 255 bytes; the size of each sub-block is declared by the byte that precedes it. 3454:

who had used licensed software to generate GIFs. Nevertheless, Unisys was subjected to thousands of online attacks and abusive emails from users believing that they were going to be charged $ 5000 or sued for using GIFs on their websites. Despite giving free licenses to hundreds of non-profit organizations, schools and governments, Unisys was completely unable to generate any good publicity and continued to be condemned by individuals and organizations such as the

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subsequent agreement was announced on 24 December 1994. Unisys stated that they expected all major commercial on-line information services companies employing the LZW patent to license the technology from Unisys at a reasonable rate, but that they would not require licensing, or fees to be paid, for non-commercial, non-profit GIF-based applications, including those for use on the on-line services.

3440:(see below) was developed in 1995 as an intended replacement. However, obtaining support from the makers of Web browsers and other software for the PNG format proved difficult and it was not possible to replace GIF, although PNG has gradually increased in popularity. Therefore, GIF variations without LZW compression were developed. For instance the libungif library, based on 2067:- output string from table 102h | 28 FF - add to table 103h 0FFh | Incoming code not found in table 103h | FF FF - add to table | - output string from table | #255 2132:

need not match the palette size: as long as the values decoded are always less than the number of colors in the palette, the symbols can be any width from 2 to 8, and the palette size any power of 2 from 2 to 256. For example, if only the first four colors (values 0 to 3) of the palette are used, the symbols can be taken to be 2 bits wide with codes starting at 3 bits.

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tiling or by layering partially transparent image blocks), the complete, full-color image appears. For example, breaking an image into tiles of 16 by 16 pixels (256 pixels in total) ensures that no tile has more than the local palette limit of 256 colors, although larger tiles may be used and similar colors merged resulting in some loss of color information.

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long as the local string can be found in a code table. There is special treatment of the first two pixels that arrive before the table grows from its initial size by additions of strings. After each output code, the local string is initialized to the latest pixel color (that could not be included in the output code).

3478:(PNG) was designed as a replacement for GIF in order to avoid infringement of Unisys' patent on the LZW compression technique. PNG offers better compression and more features than GIF, animation being the only significant exception. PNG is more suitable than GIF in instances where true-color imaging and 3311:

The size and color quality of animated GIF files can vary significantly depending on the application used to create them. Strategies for minimizing file size include using a common global color table for all frames (rather than a complete local color table for each frame) and minimizing the number of

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The pixels within each line are not interlaced, but presented consecutively from left to right. As with non-interlaced images, there is no break between the data for one line and the data for the next. The indicator that an image is interlaced is a bit set in the corresponding Image Descriptor block.

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and codes for strings that are added during the process. When the table is full the code length increases to give space for more strings, up to a maximum code 4095 = FFF(hex). As the decoder builds its table it tracks these increases in code length and it is able to unpack incoming bytes accordingly.

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105h | 28 FF FF - add to table 106h 103h | Incoming code not found in table 106h | FF FF FF - add to table | - output string from table

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An image starts with a fixed-length Image Descriptor, which may specify the presence and size of a Local Color Table (which follows next if present). The image data follows: one byte giving the bit width of the unencoded symbols (which must be at least 2 bits wide, even for bi-color images), followed

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in 2006. APNG is an extension to the PNG format as alternative to the MNG format. APNG is supported by most browsers as of 2019. APNG provides the ability to animate PNG files, while retaining backwards compatibility in decoders that cannot understand the animation chunk (unlike MNG). Older decoders

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codes available to the decoder that won't trigger an increase in code width. Because the decoder is always one step behind in maintaining the table, it does not generate a table entry upon receiving the first code from the encoder, but will generate one for each succeeding code. Thus the encoder can

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Extension blocks (blocks that "extend" the 87a definition via a mechanism already defined in the 87a spec) consist of the sentinel, an additional byte specifying the type of extension, and a series of sub-blocks with the extension data. Extension blocks that modify an image (like the Graphic Control

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GIF files start with a fixed-length header ("GIF87a" or "GIF89a") giving the version, followed by a fixed-length Logical Screen Descriptor giving the pixel dimensions and other characteristics of the logical screen. The screen descriptor may also specify the presence and size of a Global Color Table

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in the 1990s used the Application Extension block (intended to allow vendors to add application-specific information to the GIF file) to implement the Netscape Application Block (NAB). This block, placed immediately before the sequence of animation frames, specifies the number of times the sequence

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The modified encoding method ignores building the LZW table and emits only the root palette codes and the codes for CLEAR and STOP. This yields a simpler encoding (a 1-to-1 correspondence between code values and palette codes) but sacrifices all of the compression: each pixel in the image generates

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Conversely, the symbol width could be set at 8, even if only values 0 and 1 are used; these data would only require a two-color table. Although there would be no point in encoding the file that way, something similar typically happens for bi-color images: the minimum symbol width is 2, even if only

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Shorter code lengths can be used for palettes smaller than the 256 colors in the example. If the palette is only 64 colors (so color indexes are 6 bits wide), the symbols can range from 0 to 63, and the symbol width can be taken to be 6 bits, with codes starting at 7 bits. In fact, the symbol width

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For clarity the table is shown above as being built of strings of increasing length. That scheme can function but the table consumes an unpredictable amount of memory. Memory can be saved in practice by noting that each new string to be stored consists of a previously stored string augmented by one

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that can hold up to 256 entries, and the data for the image refer to the colors by their indices (0–255) in the palette table. The color definitions in the palette can be drawn from a color space of millions of shades (2 shades, 8 bits for each primary), but the maximum number of colors a frame can

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In August 1999, Unisys changed the details of their licensing practice, announcing the option for owners of certain non-commercial and private websites to obtain licenses on payment of a one-time license fee of $ 5000 or $ 7500. Such licenses were not required for website owners or other GIF users

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The LZW algorithm requires a search of the table for each pixel. A linear search through up to 4096 addresses would make the coding slow. In practice the codes can be stored in order of numerical value; this allows each search to be done by a SAR (Successive Approximation Register, as used in some

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A slight compression is evident: pixel colors defined initially by 15 bytes are exactly represented by 12 code bytes including control codes. The encoding process that produces the 9-bit codes is shown below. A local string accumulates pixel color numbers from the palette, with no output action as

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to codes that are then mapped into bytes for storing in the file. The pixel codes typically don't match the 8-bit size of the bytes, so the codes are packed into bytes by a "little-Endian" scheme: the least significant bit of the first code is stored in the least significant bit of the first byte,

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Conceptually, a GIF file describes a fixed-sized graphical area (the "logical screen") populated with zero or more "images". Many GIF files have a single image that fills the entire logical screen. Others divide the logical screen into separate sub-images. The images may also function as animation

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This byte stream is stored in the file as a series of "sub-blocks". Each sub-block has a maximum length 255 bytes and is prefixed with a byte indicating the number of data bytes in the sub-block. The series of sub-blocks is terminated by an empty sub-block (a single 0 byte, indicating a sub-block

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Since each image block can have its own local color table, a GIF file having many image blocks can be very large, limiting the usefulness of full-color GIFs. Additionally, not all GIF rendering programs handle tiled or layered images correctly. Many rendering programs interpret tiles or layers as

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To render a full-color image as a GIF, the original image must be broken down into smaller regions having no more than 255 or 256 different colors. Each of these regions is then stored as a separate image block with its own local palette and when the image blocks are displayed together (either by

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images, it is possible to do so. A GIF image can include multiple image blocks, each of which can have its own 256-color palette, and the blocks can be tiled to create a complete image. Alternatively, the GIF89a specification introduced the idea of a "transparent" color where each image block can

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The United States LZW patent expired on 20 June 2003. The counterpart patents in the United Kingdom, France, Germany and Italy expired on 18 June 2004, the Japanese patents expired on 20 June 2004, and the Canadian patent expired on 7 July 2004. Consequently, while Unisys has further patents and

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to choose it as the compression technique for their version of GIF, developed in 1987. At the time, CompuServe was not aware of the patent. Unisys became aware that the version of GIF used the LZW compression technique and entered into licensing negotiations with CompuServe in January 1993. The

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For identical 8-bit (or lower) image data, PNG files are typically smaller than the equivalent GIFs, due to the more efficient compression techniques used in PNG encoding. Complete support for GIF is complicated chiefly by the complex canvas structure it allows, though this is what enables the

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The animation delay for each frame is specified in the GCE in hundredths of a second. Some economy of data is possible where a frame need only rewrite a portion of the pixels of the display, because the Image Descriptor can define a smaller rectangle to be rescanned instead of the whole image.

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The GIF encoding process can be modified to create a file without LZW compression that is still viewable as a GIF image. This technique was introduced originally as a way to avoid patent infringement. Uncompressed GIF can also be a useful intermediate format for a graphics programmer because

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The GIF Specification allows each image within the logical screen of a GIF file to specify that it is interlaced; i.e., that the order of the raster lines in its data block is not sequential. This allows a partial display of the image that can be recognized before the full image is painted.

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can be stored in GIF files as a comment block, a plain text block, or an application-specific application extension block. Several graphics editors use unofficial application extension blocks to include the data used to generate the image, so that it can be recovered for further editing.

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Although the Graphic Control Extension block declares color index 16 (hexadecimal 10) to be transparent, that index is not used in the image. The only color indexes appearing in the image data are decimal 40 and 255, which the Global Color Table maps to black and white, respectively.

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107h 106h | Incoming code not found in table 107h | FF FF FF FF - add to table | - output string from table | #255

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without NUL characters, there are no 0 bytes in the data. Rather than break the data into formal sub-blocks, the extension block terminates with a "magic trailer" that routes any application treating the data as sub-blocks to a final 0 byte that terminates the sub-block chain.

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an output code indicating its color index. When processing an uncompressed GIF, a standard GIF decoder will not be prevented from writing strings to its dictionary table, but the code width must never increase since that triggers a different packing of bits to bytes.

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The code values shown are packed into bytes which are then packed into blocks of up to 255 bytes. A block of image data begins with a byte that declares the number of bytes to follow. The last block of data for an image is marked by a zero block-length byte.

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GIFs are suitable for sharp-edged line art with a limited number of colors, such as logos. This takes advantage of the format's lossless compression, which favors flat areas of uniform color with well defined edges. They can also be used to store low-color

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104h | FF FF 28 - add to table 103h 102h | Incoming code found in table | - output string from table | #255

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use is 256. This limitation was reasonable when GIF was developed because hardware that could display more than 256 colors simultaneously was rare. Simple graphics, line drawings, cartoons, and grey-scale photographs typically need fewer than 256 colors.

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This structure allows the file to be parsed even if not all parts are understood. A GIF marked 87a may contain extension blocks; the intent is that a decoder can read and display the file without the features covered in extensions it does not understand.

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codes or less to make the decoder reset the coding dictionary. The GIF standard allows such extra CLEAR codes to be inserted in the image data at any time. The composite data stream is partitioned into sub-blocks that each carry from 1 to 255 bytes.

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pixels covered in successive frames (so that only the pixels that change from one frame to the next are included in the latter frame). More advanced techniques involve modifying color sequences to better match the existing LZW dictionary, a form of

2012:), with only 12 magnitude comparisons. For this efficiency an extra table is needed to convert between codes and actual memory addresses; the extra table upkeeping is needed only when a new code is stored which happens at much less than pixel rate. 5240: 1069:

Each frame can designate one index as a "transparent background color": any pixel assigned this index takes on the color of the pixel in the same position from the background, which may have been determined by a previous frame of animation.

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feature, which stores image scan lines out of order in such a fashion that even a partially downloaded image was somewhat recognizable, also helped GIF's popularity, as a user could abort the download if it was not what was required.

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data for games. GIFs can be used for small animations and low-resolution video clips, or as reactions in online messaging used to convey emotion and feelings instead of using words. They are popular on social media platforms such as

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include its own palette of 255 visible colors plus one transparent color. A complete image can be created by layering image blocks with the visible portion of each layer showing through the transparent portions of the layers above.

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Compared to the GIF format, which lacks DCT compression, HEIF allows significantly more efficient compression. HEIF stores more information and produces higher-quality animated images at a small fraction of an equivalent GIF's

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magazine which publicly described the LZW technique for the first time. LZW became a popular data compression technique and, when the patent was granted, Unisys entered into licensing agreements with over a hundred companies.

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higher order bits of the code into higher order bits of the byte, spilling over into the low order bits of the next byte as necessary. Each subsequent code is stored starting at the least significant bit not already used.

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Decoding begins by mapping the stored bytes back to 9-bit codes. These are decoded to recover the pixel colors as shown below. A table identical to the one used in the encoder is built by adding strings by this rule:

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Paint does not make optimal use of GIF; due to the unnecessarily large color table (storing a full 256 colors instead of the used 2) and symbol width, this GIF file is not an efficient representation of the 15-pixel

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because of its wide implementation and portability between applications and operating systems, usage of the format has declined for space and quality reasons, often being replaced with video formats such as the

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There have been several subsequent proposals for a simple animated graphics format based on PNG using several different approaches. Nevertheless, APNG is still under development by Mozilla and is supported in

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102h 103h | Incoming code found in table | - output string from table | #40

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A small color table may suffice for small images, and keeping the color table small allows the file to be downloaded faster. Both the 87a and 89a specifications allow color tables of 2 colors for any

5034: 1084:. This ensured predictable display, but severely limited the choice of colors. When 24-bit color became the norm, palettes could instead be populated with the optimum colors for individual images. 4329: 6072: 5976: 1112: 3316:. Simply packing a series of independent frame images into a composite animation tends to yield large file sizes. Tools are available to minimize the file size given an existing GIF. 3338:(XMP) metadata standard introduced an unofficial but now widespread "XMP Data" application extension block for including XMP data in GIF files. Since the XMP data is encoded using 1014:

Each sub-block begins with a byte giving the number of subsequent data bytes in the sub-block (1 to 255). The series of sub-blocks is terminated by an empty sub-block (a 0 byte).

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All of these methods technically require the metadata to be broken into sub-blocks so that applications can navigate the metadata block without knowing its internal structure.

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of frames should be played (1 to 65535 times) or that it should repeat continuously (zero indicates loop forever). Support for these repeating animations first appeared in

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In the early days of graphical web browsers, graphics cards with 8-bit buffers (allowing only 256 colors) were common and it was fairly common to make GIF images using the

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individual pixels are accessible for reading or painting. An uncompressed GIF file can be converted to an ordinary GIF file simply by passing it through an image editor.

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Extension that specifies the optional animation delay time and optional transparent background color) must immediately precede the segment with the image they refer to.

4185: 6159: 3540:("Multiple-image Network Graphics") was originally developed as a PNG-based solution for animations. MNG reached version 1.0 in 2001, but few applications support it. 1124:

animation frames and display them in sequence as an animation with most web browsers automatically displaying the frames with a delay time of 0.1 seconds or more.

4685: 4088: 329:, and allows a separate palette of up to 256 colors for each frame. These palette limitations make GIF less suitable for reproducing color photographs and other 3970: 4644: 722:, and CompuServe employees would often quip "choosy developers choose GIF", a spoof of Jif's television commercials. However, the word is widely pronounced as 576: 6833: 5124: 2641:

animations, the GIF89a spec added the Graphic Control Extension (GCE), which allows the images (frames) in the file to be painted with time delays, forming a

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allowing text labels as text (not embedding them in the graphical data). As there is little control over display fonts, however, this feature is rarely used.

5891: 5046: 4718: 3444:'s giflib, allows creation of GIFs that followed the data format but avoided the compression features, thus avoiding use of the Unisys LZW patent. A 2001 4140: 2657:

version 2.0, and then spread to other browsers. Most browsers now recognize and support NAB, though it is not strictly part of the GIF89a specification.

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Although GIF was not designed as an animation medium, its ability to store multiple images in one file naturally suggested using the format to store the

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Following this announcement, there was widespread condemnation of CompuServe and Unisys, and many software developers threatened to stop using GIF. The

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while MNG support was dropped. APNG is currently supported by all major web browsers including Chrome (since version 59.0), Opera, Firefox and Edge.

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from 1 through 8. Most graphics applications will read and display GIF images with any of these table sizes; but some do not support all sizes when

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Decode 1st pixel 0FFh 028h | Incoming code found in table | #255

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By default, an animation displays the sequence of frames only once, stopping when the last frame is displayed. To enable an animation to loop,

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CompuServe encouraged the adoption of GIF by providing downloadable conversion utilities for many computers. By December 1987, for example, an

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Welch filed a patent application for the LZW method in June 1983. The resulting patent, US4558302, granted in December 1985, was assigned to

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An interlaced image is divided from top to bottom into strips 8 pixels high, and the rows of the image are presented in the following order:

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codes that will be used by the decoder for sequences of length greater than one. Of that upper block, the first two codes are already taken:

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patent applications relating to improvements to the LZW technique, LZW itself (and consequently GIF) have been free to use since July 2004.

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The disagreement over the pronunciation has led to heated Internet debate. On the occasion of receiving a lifetime achievement award at the

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For the sample 3×5 image above, the following 9-bit codes represent "clear" (100) followed by image pixels in scan order and "stop" (101).

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correction of PNG images was not supported before version 8, and the display of these images in earlier versions may have the wrong tint.

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In addition to the above patents, Welch's 1983 patent also includes citations to several other patents that influenced it, including:

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The code table initially contains codes that are one bit longer than the symbol size in order to accommodate the two special codes

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The feature of storing multiple images in one file, accompanied by control data, is used extensively on the Web to produce simple

8750: 7876: 6128: 5839: 5591: 5943: 5865: 5301:, Eckhart, Heinz Karl, "Verfahren zur Kompression redundanter Folgen serieller Datenelemente ", published 1982-12-02 4610: 7881: 6810: 4771: 4749: 8063: 6410: 5469: 8755: 7463: 6009: 4171: 373:

introduced GIF on 15 June 1987 to provide a color image format for their file downloading areas. This replaced their earlier

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The trivial example of a large image of solid color demonstrates the variable-length LZW compression used in GIF files.

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codes without triggering an increase in code width. Therefore, the encoder must emit extra CLEAR codes at intervals of

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Bakhshi, Saeideh; Shamma, David A.; Kennedy, Lyndon; Song, Yale; de Juan, Paloma; Kaye, Joseph "Jofish" (7 May 2016).

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8 bits/primary, the lowest 3 bits represent the bit depth minus 1, the highest true bit means that the GCT is present

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published a pair of papers on a new class of lossless data-compression algorithms, now collectively referred to as

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The maximum code may repeat for more same-color pixels.Overall data compression asymptotically approaches 3839 ×

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files were used on some websites to display simple video, but required the use of an additional browser plugin.

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Videos resolve many issues that GIFs present through common usage on the web. They include drastically smaller

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in the example define a palette of 256 colors. The indexes used in the sample image for black and white are 28

8730: 8392: 7778: 7764: 7217: 4892:"Instagrammatics and digital methods: studying visual social media, from selfies and GIFs to memes and emoji" 1042: 708: 625: 449:. GIF was one of the first two image formats commonly used on Web sites, the other being the black-and-white 17: 7758: 7211: 5705: 2004:

character. It is economical to store at each address only two words: an existing address and one character.

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Thereafter, the file is divided into segments of the following types, each introduced by a 1-byte sentinel:

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standard caused GIF to rise to prominence for the purpose of displaying short video-like files on the web.

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functions. This gives the appearance of a GIF, but with the size and speed advantages of compressed video.

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as well, meaning "to create a GIF file", as in "GIFing was the perfect medium for sharing scenes from the

7836: 6228: 5280: 5276: 5258: 158: 5809: 5257:, Kanatsu, Jiyun, "Data compression storage device", published 1982-02-02, assigned to 5254: 4794: 4110: 2240:

After the above codes are mapped to bytes, the uncompressed file differs from the compressed file thus:

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The original version of GIF was called 87a. This version already supported multiple images in a stream.

8709: 8684: 8174: 7811: 7618: 7070: 6770: 6697: 6390: 4472:"gif noun - Definition, pictures, pronunciation and usage notes | Oxford Advanced Learner's Dictionary" 948: 427: 6762: 6233: 5298: 5275: 5228: 8659: 8189: 8113: 8032: 7267: 6687: 6609: 6537: 5493: 3661: 3475: 3437: 492: 476: 341: 185: 5447: 4471: 8620: 8573: 8407: 8361: 8223: 8159: 7896: 7297: 6737: 6722: 6664: 6507: 6430: 6365: 6330: 5639: 3603: 3368: 1713: 915: 495:(PNG) standard. In 2004, all patents relating to the proprietary compression used for GIF expired. 472: 378: 337: 3308:

Browsers or other displays that do not support animated GIFs typically show only the first frame.

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An animated GIF illustrating a technique for displaying more than the typical limit of 256 colors

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For the sample image above the reversible mapping between 9-bit codes and bytes is shown below.

714:, with Wilhite stating that he intended for the pronunciation to deliberately echo the American 8664: 8397: 8244: 7871: 7108: 7049: 7037: 6891: 6742: 6589: 6512: 6094: 5888:"Chromium Blog: Chrome 32 Beta: Animated WebP images and faster Chrome for Android touch input" 5727: 5613: 3848: 3660:("High Efficiency Image File Format") is an image file format, finalized in 2015, which uses a 409: 4047: 3450:

article described a way to achieve LZW-compatible encoding without infringing on its patents.

8765: 8627: 8471: 8261: 7480: 7458: 7436: 7098: 6599: 6450: 6315: 6242: 5416: 5009:"Nullsleep - Jeremiah Johnson - Animated GIF Minimum Frame Delay Browser Compatibility Study" 3627:) tag in most web browsers, some websites use a looped version of the video tag generated by 3565: 3446: 3379: 1104: 506: 5279:, Kanatsu, Jiyun, "Data storage device", published 1986-20-24, assigned to 1045:

method; as a consequence of the relatively few colors allowed in such an image, the image's

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added support for GIF. In January 2018 Instagram also added GIF stickers to the story mode.

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for STOP. The decoder must also be prevented from using the last code in the upper block,

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Transparent background color; this is a bit field, the lowest bit signifies transparency

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frames in an animated GIF file, but again these need not fill the entire logical screen.

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but well-suited for simpler images such as graphics or logos with solid areas of color.

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is found in the newer editions of many dictionaries. In 2012, the American wing of the

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video and giving the link to the HTML player the appearance of an actual file with a

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Ending data sub-block, specifying no following data bytes (and the end of the image)

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saves a small black-and-white image as the following GIF file (illustrated enlarged).

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GIF is palette-based: the colors used in an image (a frame) in the file have their

860: 840: 802: 764: 725: 690: 638: 598: 550: 381: 261: 234: 6219: 5035:"They're different! How to match the animation rate of gif files accross [ 4907: 4757: 2621: 926:

as #JIFvsGIF) jar of peanut butter that had a label humorously declaring the soft-

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In 1989, CompuServe released an enhanced version, called 89a, This version added:

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The PNG group officially rejected APNG as an official extension on 20 April 2007.

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Beginning of first data sub-block, specifying 11 bytes of encoded data to follow

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has been disputed since the 1990s. The most common pronunciations in English are

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videos that are under 3 MB in size and 2 min in length, and in October 2014,

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add string for local code followed by first byte of string for incoming code

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Proceedings of the 2016 CHI Conference on Human Factors in Computing Systems

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videos that "require up to 95% less disk space for the same image quality."

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Size of block including application name and verification bytes (always 11)

392:, fairly large images could be downloaded reasonably quickly even with slow 8434: 8199: 7989: 7984: 7841: 7816: 7312: 6567: 6181: 5363:"Unisys Clarifies Policy Regarding Patent Use in On-Line Service Offerings" 5236: 4180: 3949: 3832: 1712:

The image pixel data, scanned horizontally from top left, are converted by

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Sample image (enlarged), actual size 3 pixels wide by 5 high

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format, which was black and white only. GIF became popular because it used

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do not support all features of PNG. Versions 6 and earlier do not support

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and their GIFV metaformat, which is really a video tag playing a looped

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Other options for web animation include serving individual frames using

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Number of bytes of LZW image data in the following sub-block, 255 bytes

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Number of bytes of LZW image data in the following sub-block: 255 bytes

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Top left pixel color chosen as the highest index of a 256-color palette

1021:

The full detail of the file format is covered in the GIF specification.

344:

technique to reduce the file size without degrading the visual quality.

8412: 8305: 7714: 7485: 7354: 7317: 7252: 7136: 7013: 6922: 6800: 6572: 6517: 6155: 6032:"#3271 (Allow using additional pixel formats with libvpx-vp9) – FFmpeg" 5973: 4084: 3828: 3807: 3628: 3620: 3607: 3429: 2642: 2634: 1165: 488: 468: 438: 370: 300: 133: 78: 5761: 4176:

is America's word of the year? Now that's what I call an omnishambles"

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A 46×46 uncompressed GIF with 7-bit symbols (128 colors, 8-bit codes).

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and Oxford Dictionaries cite both pronunciations, but place the hard

384:. Since this was more efficient than the run-length encoding used by 326: 92: 6834:

International Press Telecommunications Council § Photo metadata

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100 028 0FF 0FF 0FF 028 0FF 0FF 0FF 0FF 0FF 0FF 0FF 0FF 0FF 0FF 101

8459: 8338: 7969: 7861: 7287: 7141: 6820: 6641: 6631: 6490: 6395: 6152:"Imgur Revamps GIFs for Faster Speeds and Higher Quality with GIFV" 5510: 5480: 4283: 3324: 2649: 991:

An extension block (introduced by 0x21, an ASCII exclamation point

957: 514: 442: 389: 5520:– A project of the League for Programming Freedom (latest version) 3698:, which may be unsuitable for GIFs that combine transparency with 422:

The two versions can be distinguished by looking at the first six

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International Conference on Devices, Circuits and Systems (ICDCS)

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add string for local code followed by copy of its own first byte

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Global Color Table, color #1: transparent bit, not used in image

961: 923: 901: 676: 6921: 4208: 4147:. Oxford American Dictionaries. 13 November 2012. Archived from 4048:"You Can Finally, Actually, Really, Truly Post GIFs on Facebook" 3998:

Ajax: The Definitive Guide: Interactive Applications for the Web

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The following example shows the structure of the animation file

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restriction, and better frame-handling and compression through

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transparency without using Microsoft-specific HTML extensions.

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End of the sub-block chain for the Application Extension block

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