A standard for presenting graphical information. Developed by ZSoft for PC Paintbrush under MS-DOS. It is analogous to the BMP format. Not supported by specific graphic editors (Adobe Photoshop, Corel Draw).
It is now superseded by formats that produce better compression: GIF, JPEG, PNG. The file can contain one image of no more than 65535x65535 pixels. The number of colors can be 2, 16, 256, 16777215. The image type is raster. PCX is a device-dependent format.
It is designed to store information in the same form as in the video card. For compatibility with older programs, support for the EGA-mode video controller is required. The algorithm of such compression is fast and takes little memory, but is inefficient, impractical for compressing photos and computer graphics.
It is possible to use lossless compression. When saving, the single-color pixels that go in a row are combined, and the color is written not for each pixel, but for the whole group.
Thus, it is clear that this algorithm is useful for compressing an image in which there are areas of the same color.
The file consists of:
- Header
- Images
- VGA palettes
Pros PCX format:
- does not support grayscale images or grayscale correction tables.
- does not support CMYK colors or other systems other than RGB.
- numerous options, especially when working with colors, can make working with a file impossible.
- An inconvenient compression scheme can actually increase the size of some files.
PCX format cons:
- create a limited color palette (preferably 16 or 256).
- can not include an image with poor compression, for example, scanned.
- supported by a large number of applications.
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