The format supports up to 8 bits per pixel for each image, kra for software developer a single image to reference its own palette of up to 256 different colors chosen from the 24-bit RGB color space. This compression technique was patented in 1985. The original version of GIF was called 87a.
By December 1987, for example, an Apple IIGS user could view pictures created on an Atari ST or Commodore 64. In September 1995 Netscape Navigator 2. 0 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. In May 2015 Facebook added GIF support, even though they originally did not support GIF on their site. As a noun, the word GIF is found in the newer editions of many dictionaries.
A humorous image announcing the launch of a White House Tumblr suggests pronouncing GIF with the hard “G” sound. The American Heritage Dictionary cites both, indicating “jif” as the primary pronunciation, while Cambridge Dictionary of American English offers only the hard-“G” pronunciation. The disagreement over the pronunciation led to heated Internet debate. This takes advantage of the format’s lossless compression, which favors flat areas of uniform color with well defined edges. GIFs may be used to store low-color sprite data for games. GIFs can be used for small animations and low-resolution video clips.
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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. 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. 0x21, an ASCII exclamation point ‘! This structure allows the file to be parsed even if not all parts are understood.
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. 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. GIF images using the websafe palette. 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. Tables of 2, 16, and 256 colors are widely supported.
Although GIF is almost never used for true color 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. 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. Since each image block requires its own local color table, a GIF file having lots of 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.