PPM to DJVU Converter

PPM (Portable Pixmap) is the full-color member of the Netpbm image format family, created by Jef Poskanzer in 1988 as part of the Pbmplus toolkit for Unix systems. PPM stores RGB color images where each pixel contains three values (red, green, blue) ranging from 0 to a specified maximum, typically 255 for 8-bit-per-channel or 65535 for 16-bit-per-channel color. The format exists in ASCII (magic number P3), where pixel values are written as decimal numbers in row-major order, and binary (magic number P6), where values are stored as raw bytes for compact representation. Both variants begin with a plain-text header: magic number, width, height, and maximum color value. PPM completes the Netpbm trio alongside PBM (monochrome) and PGM (grayscale), serving as the universal color image intermediate in the convert-process-convert pipeline that defined Netpbm's approach to format interoperability. One advantage is absolute simplicity — PPM requires no compression libraries, container parsing, or metadata handling, making it the easiest full-color format to implement from scratch in any programming language. The format's widespread adoption in scientific computing and computer graphics education is another practical strength: PPM serves as a standard I/O format for ray tracers, image processing coursework, and visualization tools where implementation simplicity outweighs file size concerns. PPM is supported by ImageMagick, GIMP, and virtually all image processing libraries.