Microsoft KB Archive/72520

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The information in this article applies to:


 * Microsoft Paintbrush for MS-DOS, versions 4.0, 4.01

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SUMMARY
MS Paintbrush and PC Paintbrush both store images as bitmaps in video memory. The PCX file format is a special Paintbrush format for a bitmap image. The PCX format compresses the file to save disk space.

MORE INFORMATION
Creation of pictures on the computer screen is normally done with either of two basic techniques: raster graphics or vector graphics. Bitmapped images are re-created on the screen using the raster graphics technique. Discussion of the two graphics techniques follows:

Raster Graphics
Raster graphics creates an image on the screen by drawing numerous horizontal rows of light across the screen with an electron beam. Each horizontal row is made up of small phosphorescent dots of illumination. These dots of light are called &quot;pixels&quot; and are the smallest unit of illumination on the screen.

When a picture file is created, the image is stored in video memory as a series of bits with each pixel being assigned a certain number of bits. In the simplest monochrome display, one bit can be assigned to each pixel. Therefore, an individual pixel is illuminated or not depending on whether the corresponding bit in video memory is on or off.

For color and gray-scale displays, more bits are needed to properly illuminate each pixel. In other words, as the number of colors or shades of gray increase in the image, the number of bits in video memory also increases to reflect the subtleties of color and shade.

While the Paintbrush PCX file format is essentially a bitmapped representation of an image, it has the special feature of being compressed to save disk storage space. The fact that lines and edges of figures in Paintbrush images often have a jagged or stair-stepped appearance may be attributed to the fact that the images are composed of the individual dots or pixels. The higher the resolution of the display, the smaller the pixels are, and therefore, the irregular edges seem less pronounced.

PC Paintbrush, version 3.0, allows the option of saving files in the following formats: PCX

monochrome bitmap

16-color bitmap

256-color bitmap

24-color bitmap The Windows version of Paintbrush loads files with the BMP, MSP, and PCX file extensions.

Version 4.0 of Paintbrush for MS-DOS allows you to save an image in PCX, TIF, or TIF uncompressed file format; you may load a file with either the PCX or TIF extensions. Version 2.0 of Paintbrush for MS-DOS allows you to save or load files as PCX, PCC, or GX1 (Showpartner) bitmap file formats.

Other examples of bitmap-image file formats include: HPGL - Hewlett-Packard Graphics Language

EPS(F) - Encapsulated PostScript (Format)

TIFF - Tag Image File Format

Vector Graphics
Vector graphics involves creating an image on the computer screen as a series of geometric shapes, such as points, lines, and arcs. The drawing is stored as a series of entries in a vector table where a straight line might be represented only by the coordinates of its end points, and a circle may be represented by a series of small straight lines. Vector graphics is the method of display that is used by CAD (computer-aided design) programs, such as EasyCAD and AutoCAD. To display vector graphics on the raster graphics screen found on most personal computers, the vectors must be converted to pixels. This process is known as the &quot;rasterization&quot; of vectors.