GIF - Wikipedia, the free encyclopedia. The Graphics Interchange Format (better known by its acronym GIFJIF or GHIF) is a bitmapimage format that was developed by US- based software writer Steve Wilhite while working at the internet service provider Compu. Serve in 1. 98. 7. It also supports animations and allows a separate palette of up to 2. These palette limitations make the GIF format less suitable for reproducing color photographs and other images with continuous color, but it is well- suited for simpler images such as graphics or logos with solid areas of color. GIF images are compressed using the Lempel. This compression technique was patented in 1. Controversy over the licensing agreement between the software patent holder, Unisys, and Compu. Serve in 1. 99. 4 spurred the development of the Portable Network Graphics (PNG) standard. By 2. 00. 4 all the relevant patents had expired. History. GIF became popular because it used LZW data compression, which was more efficient than the run- length encoding that formats such as PCX and Mac. Paint used, and fairly large images could therefore be downloaded in a reasonably short time, even with very slow modems. Facebook Graphics, Glitter Graphics, Animated Gifs Navigation: Home: Animated GIFs Animals Anime Cartoons Celebrities Cute Stuff Dancing Emo Fantasy Flowers Funny Geography Girl Thing Guy Thing. Search for your perfect graphic. The original version of the GIF format was called 8. The 8. 9a 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 . By December 1. 98. Apple IIGS user could view pictures created on an Atari ST or Commodore 6. 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. In 2. 01. 2, the American wing of the Oxford University Press recognized GIF as a verb as well, meaning . The press's lexicographers voted it their word of the year, saying that GIFs have evolved into . Steve Wilhite says that the intended pronunciation deliberately echoes the American peanut butter brand Jif, and Compu. Serve employees would often say . Merriam- Webster's Collegiate Dictionary. The New Oxford American Dictionary gave only . On the occasion of receiving a lifetime achievement award at the 2. Animated Graphic ProgrammingArena Animation International Program (AAIP - Broadcast) MULTIMEDIA. Web Design & Development Program (WDP) Multimedia Design Program (MDP) Design & Publishing Program (DPP) SHORT TERM COURSES. Webby Award ceremony, Wilhite rejected the alternative pronunciation. This takes advantage of the format's lossless compression, which favors flat areas of uniform color with well defined edges. One or more video sources can be edited, rearranged, or combined to create an absurd juxtaposition, to create the opposite effect intended by the creator of the original work, or to emphasize and exaggerate a minor detail. File format. 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 (. Xara is renowned for making quality website and graphic design software for professionals and novices at a price which won't break the bank. Graphic Design & 3-D Animation/Game Design Pre-College Program. Incorporate animated elements into a game environment using Unity 3D. Week 2: Brand Yourself! Graphic design, 3-D printing, photography. 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 0x. C, a comma ',')An extension block (introduced by 0x. The trailer (a single byte of value 0x. B, a semi- colon '; '), 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 . 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 2. 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 8. 7a 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. Due to the reduced number of colors in the image, there are display issues. 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 2. The color definitions in the palette can be drawn from a color space of millions of shades (2. 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 2. Each frame can designate one index as a . These techniques sacrifice spatial resolution to approximate deeper color resolution. While not part of the GIF specification, dithering can of course 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. Now that 3. 2- bit graphics cards, which support 2. Both the 8. 7a and 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, 1. 6, and 2. True color. Alternatively, the GIF8. 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 2. 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 1. Many rendering programs interpret tiles or layers as animation frames and display them in sequence as an endless animation. Paint does not make optimal use of the GIF format; due to the unnecessarily large color table (storing a full 2. GIF file is not an efficient representation of the 1. Although the Graphics Control Extension block declares color index 1. The only color indexes appearing in the image data are decimal 4. 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. The pixel codes typically don't match the 8- bit size of the bytes, so the codes are packed into bytes by a . 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 . Each sub- block has a maximum length 2. 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. Binary. Bytes(hex)0. 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). 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 4. 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 1. 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. 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. Is incoming code found in table? If the palette is only 6. 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 2. 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 2- 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.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. Archives
December 2016
Categories |