Graphic Interchange Format. Raster graphics image file type.
8-Bit-per-pixel bitmap image format. This format is widely used on the internet due to wide support and portability. This format is not suitable for continuous coloured images such as photographs as it has a limited colour palette (256), it is better suited for graphics with solid coloured areas. GIF is a lossless data compression method known as the Lempel-Ziv-Welch (LZW) compression technique, it reduces file size without being detrimental to image quality and leaves sharp edges clearly defined unlike JPEGs. It compresses at ratios between 3:1 and 5:1.
The GIF format was developed in 1987 by Compuserve who needed a platform independent image format suitable for transfer across slow connections. Currently there are 2 standard GIFs 87a and 89a. Enhancements to 89a included interlacing, ability to define one colour to be transparent and ability to store multiple images in one file to create basic animations.
Portable Network Graphics (PNG) is a popular alternative to GIF, this is not limited to a 256 colour palette and is better compressed, however PNG can only be used for still images and not animations.
When exporting to GIF (*.gif) the following Raster Exporter Configuration dialog is displayed:
Configuration
Pixel Size
This option allows you to specify the image resolution.
Image Width/Height
This option allows you to specify the output file size in pixels for width and height and the pixel size is in map units.
Colour Palette
Algorithm used to generate the colour palette, select from 5x5x5 Colour Cube, 6x6x6 Colour Cube, Neural Network Quantization, Oct Tree.
Create Worldfile
True or False, to create worldfile containing georeferencing information.
Dithering Algorithm
Select from Dither (GDI), Floyd-Steinberg, SIS, Snap (GDI), Snap (Palette).
Interlacing method
Interlacing method for image display, True or False.
See full list of Export Formats
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