ImageGear .NET - Updated
User Guide > File Formats and Compressions > File Formats > File Formats Reference > PPM
Full Name PPM (Portable Pixmap File Format)
Format ID ImGearFormats.PBM (See the Note below)
File Extension(s) *.ppm
Data Type Raster Image
Data Encoding Binary
Multi-Page Support No
Alpha Channel Support No
Metadata Update Support No
ImageGear Platforms Support WIN32, WIN64, Unix, Unix64, .NET, .NET64, MAC
ImageGear supports PPM file format via its PBM format filter. Use ImGearFormats.PBM to save images to PPM format.

ImageGear Supported Versions

October 1991 - last release

ImageGear Supported Features

ImageGear Read Support

ImageGear Write Support

ImageGear Filter Control Parameters



The PPM format is useful for quick and easy transfer of color bitmap images. This format, as well as the PBM, PGM, and PNM formats, are at the core of a set of utility programs also written by Jef Poskanzer. These formats serve as intermediary storage methods for the conversion of other file formats. For example, a method called gifftoppm translates a GIF file to a PPM, where it can translate to a TIFF using the pnmtotiff.

The Portable Pixmap File Format structure is very simple. It begins with a short ASCII header that contains the file type identifier (magic number), the width and height of the image, a "maximum color-component value", and perhaps a comment line identifying the filename. Following white space (usually a carriage return) is the bitmap data. The number of pixels is equal to width * height, with each pixel being represented by three bytes: one each for Red, Green, and Blue color components, respectively.

The magic number of the header can have one of two values: either P3 or P6. P3 indicates that the bitmap data is read as ASCII decimal values. P6 indicates that the bitmap data is stored as plain bytes. This makes for a smaller and faster-to-read file.

If the maximum gray value exceeds 255 (28 = 256 gray values from 0 to 255), each pixel is represented by three 16-bit RGB samples, making a total of 48 bits per pixel. ImageGear loads such images to 24-bit RGB.

References Used

Kay, David C. and John R. Levine. Graphics File Formats, 2nd ed. Windcrest /McGraw-Hill, 1995.

PPM Specification by Jef Poskanzer, copyright A 1989, 1991.

See Also