Best gif ever download

The Graphics Interchange Format (GIF; /dʒɪf/JIF or /ɡɪf/GHIF) is a bitmapimage format that was developed by a team at the online services provider CompuServe led by American computer scientist Steve Wilhite on 15 June ^[1] It has since come into widespread usage on the World Wide Web due to its wide support and portability between applications and operating systems.

The format supports up to 8 bits per pixel for each image, allowing a single image to reference its own palette of up to different colors chosen from the bit RGB color space. It also supports animations and allows a separate palette of up to colors for each frame. These palette limitations make GIF less suitable for reproducing color photographs and other images with color gradients, but well-suited for simpler images such as graphics or logos with solid areas of color. Unlike video, the GIF file format does not support audio.

GIF images are compressed using the Lempel–Ziv–Welch (LZW) lossless data compression technique to reduce the file size without degrading the visual quality. This compression technique was patented in Controversy over the licensing agreement between the software patent holder, Unisys, and CompuServe in spurred the development of the Portable Network Graphics (PNG) standard. By all the relevant patents had expired.

History[edit]

CompuServe introduced GIF on 15 June to provide a color image format for their file downloading areas. This replaced their earlier run-length encoding format, which was black and white only. GIF became popular because it used LZW data compression. Since this was more efficient than the run-length encoding used by PCX and MacPaint, fairly large images could be downloaded reasonably quickly even with slow modems.

The original version of GIF was called 87a.^[1] In , CompuServe released an enhanced version, called 89a,^[2] which added support for animation delays (multiple images in a stream were already supported in 87a), transparent background colors, and storage of application-specific metadata. The 89a specification also supports incorporating text labels as text (not embedding them in the graphical data), but as there is little control over display fonts, this feature is not widely used. The two versions can be distinguished by looking at the first six bytes of the file (the "magic number" or signature), which, when interpreted as ASCII, read "GIF87a" and "GIF89a", respectively.

CompuServe encouraged the adoption of GIF by providing downloadable conversion utilities for many computers. By December , for example, an Apple IIGS user could view pictures created on an Atari ST or Commodore ^[3] GIF was one of the first two image formats commonly used on Web sites, the other being the black-and-white XBM.^[4]

In September Netscape Navigator added the ability for animated GIFs to loop.

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

The optional interlacing 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,^[5] as a user could abort the download if it was not what was required.

In May Facebook added support for GIF.^[6][7] In January Instagram also added GIF stickers to the story mode.^[8]

Terminology[edit]

As a noun, the word GIF is found in the newer editions of many dictionaries. In , the American wing of the Oxford University Press recognized GIF as a verb as well, meaning "to create a GIF file", as in "GIFing was perfect medium for sharing scenes from the Summer Olympics". The press's lexicographers voted it their word of the year, saying that GIFs have evolved into "a tool with serious applications including research and journalism".^[9][10]

Pronunciation of GIF[edit]

The creators of the format pronounced the word as "jif" with a soft "G"/dʒɪf/ as in "gym". Steve Wilhite says that the intended pronunciation deliberately echoes the American peanut butter brand Jif, and CompuServe employees would often say "Choosy developers choose GIF", spoofing this brand's television commercials.^[11] The word is now also widely pronounced with a hard "G"/ɡɪf/ as in "gift".^[12] In , an informal poll on programming website Stack Overflow showed some numerical preference for hard-"G" pronunciation,^[13] especially among respondents in eastern Europe, though both soft-"G" and enunciating each letter individually were found to be popular in Asia and emerging countries.^[14]

The American Heritage Dictionary^[15] cites both, indicating "jif" as the primary pronunciation, while Cambridge Dictionary of American English^[16] offers only the hard-"G" pronunciation. Merriam-Webster's Collegiate Dictionary^[17] and the OED cite both pronunciations, but place "gif" in the default position ("\ˈgif, ˈjif\").^[18] The New Oxford American Dictionary gave only "jif" in its 2nd edition^[19] but updated it to "jif, gif" in its 3rd edition.^[20]

The disagreement over the pronunciation led to heated Internet debate. On the occasion of receiving a lifetime achievement award at the Webby Award ceremony, Wilhite rejected the hard-"G" pronunciation,^[12][21][22] and his speech led to 17, posts on Twitter and 50 news articles.^[23] The White House^[12] and TV program Jeopardy! also entered the debate during ^[22]

In February , The J.M. Smucker Company, the owners of the Jif peanut butter brand, partnered with animated image database and search engine Giphy to release a limited-edition "Jif vs. GIF" (hashtagged as #JIFvsGIF) jar of Jif peanut butter that has a label humorously declaring the soft-"G" pronunciation to exclusively refer to the peanut butter, and GIF to be exclusively pronounced with the hard-"G" pronunciation.^[24]

Usage[edit]

• 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.^[25]
• GIFs may be used to store low-color sprite data for games.^[26]
• GIFs can be used for small animations and low-resolution video clips.^[26]
• GIFs can be used as a reaction when messaging online, used to convey emotion and feelings, alternative to using words
• Popular on social media platforms such as Tumblr, Facebook and Twitter.

File format[edit]

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

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, which follows next if present.

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

• An image (introduced by 0x2C, an ASCII comma )
• An extension block (introduced by 0x21, an ASCII exclamation point )
• The trailer (a single byte of value 0x3B, an ASCII semicolon ), which should be the last byte of the file.

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 by a linked list of sub-blocks containing the LZW-encoded data.

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 linked list of sub-blocks with the extension data. Extension blocks that modify an image (like the Graphic Control Extension that specifies the optional animation delay time and optional transparent background color) must immediately precede the segment with the image they refer to.

The linked lists used by the image data and the extension blocks consist of series of sub-blocks, each sub-block beginning with a byte giving the number of subsequent data bytes in the sub-block (1 to ). The series of sub-blocks is terminated by an empty sub-block (a 0 byte).

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.

The full detail of the file format is covered in the GIF specification.^[2]

Palettes[edit]

GIF is palette-based: the colors used in an image (a frame) in the file have their RGB values defined in a palette table that can hold up to entries, and the data for the image refer to the colors by their indices (0–) in the palette table. The color definitions in the palette can be drawn from a color space of millions of shades (2²⁴ shades, 8 bits for each primary), but the maximum number of colors a frame can use is This limitation seemed reasonable when GIF was developed because few people could afford the hardware to display more colors simultaneously. Simple graphics, line drawings, cartoons, and grey-scale photographs typically need fewer than colors.

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.

Many techniques, collectively called dithering, 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.

In the early days of graphical web browsers^[when?], graphics cards with 8-bit buffers (allowing only colors) were common and it was fairly common to make GIF images using the websafe palette.^{[according to whom?]} This ensured predictable display, but severely limited the choice of colors. When bit color became the norm palettes could instead be populated with the optimum colors for individual images.

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 2ⁿ colors for any n 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 creating images. Tables of 2, 16, and colors are widely supported.

True color[edit]

Although GIF is almost never used for true color images, it is possible to do so.^[27][28] A GIF image can include multiple image blocks, each of which can have its own 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 include its own palette of 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.

To render a full-color image as a GIF, the original image must be broken down into smaller regions having no more than or 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 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 ( pixels in total) ensures that no tile has more than the local palette limit of colors, although larger tiles may be used and similar colors merged resulting in some loss of color information.^[27]

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.^[28] Additionally, not all GIF rendering programs handle tiled or layered images correctly. Many rendering programs interpret tiles or layers as animation frames and display them in sequence as an endless animation^[27] with most web browsers automatically displaying the frames with a delay time of seconds or more.^{[29][30][better&#;source&#;needed]}

Example GIF file[edit]

Microsoft Paint saves a small black-and-white image as the following GIF file. Paint does not make optimal use of GIF; due to the unnecessarily large color table (storing a full colors instead of the used 2) and symbol width, this GIF file is not an efficient representation of the pixel image (illustrated enlarged above).

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 , which the Global Color Table maps to black and white, respectively.

Note that the hex numbers in the following tables are in little-endian byte order, as the format specification prescribes.

byte# hexadecimal text or(hex) value Meaning 0: 47 49 46 38 39 61 GIF89a Header Logical Screen Descriptor 6: 03 00 3 - logical screen width in pixels 8: 05 00 5 - logical screen height in pixels A: F7 - GCT follows for colors with resolution 3 × 

Image coding[edit]

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

This byte stream is stored in the file as a series of "sub-blocks". Each sub-block has a maximum length 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 with 0 data bytes).

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

9-bit code (hex)	Binary	Bytes (hex)
|	00
|1	51
|00	FC
0FF
|	1B
|	28
|	70
10|	A0
1|	C1
|	83
	01
|1	01

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 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).

Table 9-bitstring --> code code Action

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

The LZW algorithm requires a search of the table for each pixel. A linear search through up to 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 ADCs), 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.

Image decoding[edit]

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:

Yes	add string for local code followed by first byte of string for incoming code
No	add string for local code followed by copy of its own first byte

shift9-bit > Local Table Pixelcode code code --> string Palette color Action h h | #0 Initialize root table of 9-bit codes : | palette : | colors 0FFh | # h | clr h | end h | #40 BLACK Decode 1st pixel 0FFh h | Incoming code found in table | # WHITE - output string from table h | 28 FF - add to table h 0FFh | Incoming code not found in table h | FF FF - add to table | - output string from table | # WHITE | # WHITE h h | Incoming code found in table | - output string from table | #40 BLACK | # WHITE h | FF FF 28 - add to table h h | Incoming code found in table | - output string from table | # WHITE | # WHITE h | 28 FF FF - add to table h h | Incoming code not found in table h | FF FF FF - add to table | - output string from table | # WHITE | # WHITE | # WHITE h h | Incoming code not found in table h | FF FF FF FF - add to table | - output string from table | # WHITE | # WHITE | # WHITE | # WHITE h | End

LZW code lengths[edit]

Shorter code lengths can be used for palettes smaller than the 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 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 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.

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 values 0 and 1 are used.

The code table initially contains codes that are one bit longer than the symbol size in order to accommodate the two special codes clr and end 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 = FFF(hex). As the decoder builds its table it tracks these increases in code length and it is able to unpack incoming bytes accordingly.

Uncompressed GIF[edit]

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 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.

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 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.

If the symbol width is n, the codes of width n+1 fall naturally into two blocks: the lower block of 2ⁿ codes for coding single symbols, and the upper block of 2ⁿ 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: 2ⁿ for CLEAR and 2ⁿ + 1 for STOP. The decoder must also be prevented from using the last code in the upper block, 2ⁿ⁺¹ − 1, because when the decoder fills that slot, it will increase the code width. Thus in the upper block there are 2ⁿ − 3 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 generate 2ⁿ − 2 codes without triggering an increase in code width. Therefore, the encoder must emit extra CLEAR codes at intervals of 2ⁿ − 2 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 bytes.

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

9-bit codes: 0FF 0FF 0FF 0FF 0FF 0FF 0FF 0FF 0FF 0FF 0FF 0FF 0FF

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

: 14 20 20 bytes uncompressed image data follow 00 51 FC FB F7 0F C5 BF 7F FF FE FD FB F7 EF DF BF 7F 01 01 00 - end :

Compression example[edit]

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

Code			Pixels		Notes
No. Ni	Value Ni +	Length (bits)	This code Ni	Accumulated Ni(Ni + 1)/2	Relations using Ni only apply to same- color pixels until coding table is full.
0	h	9	Clear code table
1	FFh		1	1	Top left pixel color chosen as the highest index of a color palette
2	h		2	3
3 ⋮	h ⋮ 1FFh		3 ⋮	6 ⋮	Last 9-bit code
⋮	h ⋮ 3FFh	10	⋮	⋮	Last bit code
⋮	h ⋮ 7FFh	11	⋮	⋮	Last bit code
⋮	h ⋮ FFFh	12	⋮	⋮	Code table full
⋮	FFFh			The maximum code may repeat for more same-color pixels. Overall data compression asymptotically approaches × 8/ 12 = +1/3
h	End of image data

The code values shown are packed into bytes which are then packed into blocks of up to 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.

Interlacing[edit]

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.

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:

• Pass 1: Line 0 (the top-most line) from each strip.
• Pass 2: Line 4 from each strip.
• Pass 3: Lines 2 and 6 from each strip.
• Pass 4: Lines 1, 3, 5, and 7 from each strip.

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.

Animated GIF[edit]

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 frames of an animation sequence. To facilitate displaying 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 video clip. 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 bytes; the size of each sub-block is declared by the byte that precedes it.

By default, an animation displays the sequence of frames only once, stopping when the last frame is displayed. To enable an animation to loop, Netscape in the s 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).^[31] This block, placed immediately before the sequence of animation frames, specifies the number of times the sequence of frames should be played (1 to times) or that it should repeat continuously (zero indicates loop forever). Support for these repeating animations first appeared in Netscape Navigator version , and then spread to other browsers.^[32] Most browsers now recognize and support NAB, though it is not strictly part of the GIF89a specification.

The following example shows the structure of the animation file Rotating earth (large).gif shown (as a thumbnail) in the article's infobox.

byte# hexadecimal text or(hex) value Meaning 0: 47 49 46 38 39 61 GIF89a HeaderLogical Screen Descriptor 6: 90 01 - width in pixels 8: 90 01 - height in pixels A: F7 - GCT follows for colors with resolution 3 x 8bits/primary B: 00 0 - background color #0 C: 00 - default pixel aspect ratio D: Global Color Table : 30D: 21 FF Application Extension block 30F: 0B 11 - eleven bytes of data follow 4E 45 54 53 43 41 50 45 NETSCAPE - 8-character application name 32 2E 30 - application "authentication code" 31B: 03 3 - three more bytes of data 31C: 01 1 - index of the current data sub-block (always 1 for the NETSCAPE block) 31D: FF FF - unsigned number of repetitions 31F: 00 - end of App Extension block 21 F9 Graphic Control Extension for frame #1 04 4 - four bytes in the current block 04 - reserved; 5 lower bits are bit field - disposal method 1: do not dispose - no user input - transparent color is not given 09 00 - sec delay before painting next frame FF - transparent color index (unused in this frame) 00 - end of GCE block 2C Image Descriptor of frame #1 00 00 00 00 (0,0) - NW corner of frame at 0, 0 32D: 90 01 90 01 (,) - Frame width and height:  ×  00 - no local color table; no interlace 08 8 LZW min code size; Image Data of frame #1 beginning FF - bytes of LZW encoded image data follow data FF - bytes of LZW encoded image data follow data : 92C0: 00 - end of LZW data for this frame 92C1: 21 F9 Graphic Control Extension for frame #2 : : EDABD: 21 F9 Graphic Control Extension for frame #44 : F48F5: 3B File terminator

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

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 pixels covered in successive frames (so that only the pixels that change from one frame to the next are included in the latter frame). Simply packing a series of independent frame images into a composite animation tends to yield large file sizes.

Internet Explorer slows down GIFs if the frame-rate is 20 frames per second or higher and Microsoft reports that Google Chrome and Safari also slow down some GIF animations.^[33]

Starting in early , the University of Ulm used animated GIF as live video streaming format to show a controllable model railroad.

Metadata[edit]

Metadata 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.

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.

The Extensible Metadata Platform (XMP) metadata standard introduced an unofficial but now widespread "XMP Data" application extension block for including XMP data in GIF files.^[34] Since the XMP data is encoded using UTF-8 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.

Unisys and LZW patent enforcement[edit]

In and , Jacob Ziv and Abraham Lempel published a pair of papers on a new class of lossless data-compression algorithms, now collectively referred to as LZ77 and LZ In , Terry Welch developed a fast variant of LZ78 which was named Lempel–Ziv–Welch (LZW).^[35][36]

Welch filed a patent application for the LZW method in June The resulting patent, US &#;, granted in December , was assigned to Sperry Corporation who subsequently merged with Burroughs Corporation in and formed Unisys.^[35] Further patents were obtained in the United Kingdom, France, Germany, Italy, Japan and Canada.

In addition to the above patents, Welch's patent also includes citations to several other patents that influenced it, including two Japanese patents (JPA and JPA) from NEC's Jun Kanatsu, U.S. Patent 4,, () from John S. Hoerning, U.S. Patent 4,, () from Klaus E. Holtz, and a Dutch patent (DE) from Karl Eckhart Heinz.^[37]

In June , an article by Welch was published in the IEEE magazine which publicly described the LZW technique for the first time.^[38] LZW became a popular data compression technique and, when the patent was granted, Unisys entered into licensing agreements with over a hundred companies.^[35][39]

The popularity of LZW led CompuServe to choose it as the compression technique for their version of GIF, developed in At the time, CompuServe was not aware of the patent.^[35] Unisys became aware that the version of GIF used the LZW compression technique and entered into licensing negotiations with CompuServe in January The subsequent agreement was announced on 24 December ^[36] 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.^[39]

Following this announcement, there was widespread condemnation of CompuServe and Unisys, and many software developers threatened to stop using GIF. The PNG format (see below) was developed in as an intended replacement.^[35][36][38] 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.^[35] Therefore, GIF variations without LZW compression were developed. For instance the libungif library, based on Eric S. Raymond's giflib, allows creation of GIFs that followed the data format but avoided the compression features, thus avoiding use of the Unisys LZW patent.^[40] A Dr. Dobb's article described another alternative to LZW compression, based on square roots.^[41]

In August , 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 $ or $^[42] Such licenses were not required for website owners or other GIF users 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 $ or sued for using GIFs on their websites.^[43] 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 League for Programming Freedom who started the "Burn All GIFs" campaign in ^[44][45]

The United States LZW patent expired on 20 June ^[46] The counterpart patents in the United Kingdom, France, Germany and Italy expired on 18 June , the Japanese patents expired on 20 June , and the Canadian patent expired on 7 July ^[46] Consequently, while Unisys has further patents and patent applications relating to improvements to the LZW technique,^[46] GIF may now be used freely.^[47]

Alternatives[edit]

PNG[edit]

Portable Network Graphics (PNG) was designed as a replacement for GIF in order to avoid infringement of Unisys' patent on the LZW compression technique.^[35] PNG offers better compression and more features than GIF,^[48] animation being the only significant exception. PNG is more suitable than GIF in instances where true-color imaging and alpha transparency are required.

Although support for PNG format came slowly, new web browsers generally support PNG. Older versions of Internet Explorer do not support all features of PNG. Versions 6 and earlier do not support alpha channel transparency without using Microsoft-specific HTML extensions.^[49]Gamma correction of PNG images was not supported before version 8, and the display of these images in earlier versions may have the wrong tint.^[50]

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.^[51] Complete support for GIF is complicated chiefly by the complex canvas structure it allows, though this is what enables the compact animation features.

Animation formats[edit]

Videos resolve many issues that GIFs present through common usage on the web. They include drastically smaller file sizes, the ability to surpass the 8-bit color restriction, and better frame-handling and compression through codecs. Virtually universal support for the GIF format in web browsers and a lack of official support for video in the HTML standard caused GIF to rise to prominence for the purpose of displaying short video-like files on the web.

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

In , an extension to the PNG format called APNG ("Animated Portable Network Graphics") was proposed as alternative to the MNG format by Mozilla. APNG is supported by most browsers as of ^[52] APNG provide the ability to animate PNG files, while retaining backwards compatibility in decoders that cannot understand the animation chunk (unlike MNG). Older decoders will simply render the first frame of the animation. The PNG group officially rejected APNG as an official extension on 20 April ^[53] There have been several subsequent proposals for a simple animated graphics format based on PNG using several different approaches.^[54] Nevertheless, Animated Portable Network Graphics is still under development by Mozilla and is supported in Firefox 3^[55][56] while MNG support was dropped.^[57][58] APNG is currently supported by all major web browsers including Chrome since version and Opera and Firefox and Edge.

Embedded Adobe Flash objects and MPEGs are used on some websites to display simple video, but require the use of an additional browser plugin. WebM and WebP are in development and are supported by some web browsers.^[59] Other options for web animation include serving individual frames using AJAX, or animating SVG images using JavaScript or SMIL ("Synchronized Multimedia Integration Language").^{[citation needed]}

With the introduction of widespread support of the HTML5 video () tag in most web browsers, some websites use a looped version of the video tag generated by JavaScript functions. This gives the appearance of a GIF, but with the size and speed advantages of compressed video. Notable examples are Gfycat and Imgur and their GIFV metaformat, which is really a video tag playing a looped MP4 or WebM compressed video.^[60]

High Efficiency Image File Format (HEIF) is an image file format, finalized in , which uses a discrete cosine transform (DCT) lossy compression algorithm based on the HEVC video format, and related to the JPEG image format. In contrast to JPEG, HEIF supports animation.^[61] 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 size.^[62]

VP9 only supports alpha compositing with chroma subsampling^[63] in the YUVA pixel format, which may be unsuitable for GIFs that combine transparency with rasterisedvector graphics with fine color details.

Uses[edit]

In April , 4chan added support for silent WebM videos that are under 3 MB in size and 2 min in length,^[64][65] and in October , Imgur started converting any GIF files uploaded to the site to video and giving the link to the HTML player the appearance of an actual file with a extension.^[66]