Compression

Many image file formats use compression techniques to reduce the storage space required by bitmap image data. Compression techniques are distinguished by whether they remove detail and colour from the image. Lossless techniques compress image data without removing detail; lossy techniques compress images by removing detail. The following are commonly used compression techniques:

Run Length Encoding (RLE) is a lossless compression technique supported by the Photoshop and TIFF file formats and some common Windows file formats.

Lemple-Zif-Welch (LZW) is a lossless compression technique supported by TIFF, PDF, GIF, and PostScript language file formats. This technique is most useful in compressing images that contain large areas of single colour, such as screenshots or simple paint images.

Joint Photographic Experts Group (JPEG) is a lossy compression technique supported by JPEG, PDF, and PostScript language file formats. JPEG compression provides the best results with continuous-tone images, such as photographs, when the size of the file is an important factor.

ZIP encoding is a lossless compression technique supported by the PDF file format. Like LZW, ZIP compression is most effective for images that contain large areas of single colour.

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