PNM to RGBO Converter

RGBO is a raw pixel data format designation used by ImageMagick, the open-source image processing suite first released in 1990, representing images as a flat sequence of Red, Green, Blue, and Opacity (inverted alpha) sample values with no header, container, or compression. The RGBO channel ordering specifies that the fourth channel is opacity rather than alpha — where alpha represents transparency (0 = transparent, max = opaque), opacity represents the inverse (0 = opaque, max = transparent). This distinction matters in compositing pipelines where the mathematical convention for the fourth channel varies between systems: some compositing models work with alpha (transparency), while older conventions including portions of ImageMagick's internal processing historically used opacity. RGBO files contain raw sample data at a user-specified bit depth (8-bit, 16-bit, or floating-point per channel), with pixels stored in scanline order. Because there is no header, the image dimensions, bit depth, and endianness must be specified externally when reading the file — typically via ImageMagick command-line arguments. One advantage is direct compatibility with processing pipelines that use the opacity convention: RGBO eliminates the need for channel inversion when interfacing with systems that expect opacity rather than alpha, preventing subtle compositing errors that occur when transparency conventions are mixed. The format's raw-data nature provides another practical benefit — with no encoding overhead, RGBO data can be memory-mapped, processed with SIMD instructions, or piped between processes with minimal latency. RGBO is primarily used within ImageMagick processing chains and can be converted to any other format using ImageMagick's extensive format support.