DJVU to RGBA Converter

RGBA is a raw (headerless) image format that extends the RGB color model with a fourth channel for alpha transparency. Each pixel is stored as four consecutive sample values — red, green, blue, and alpha — written sequentially in scanline order with no container structure, headers, or compression. The alpha channel specifies opacity for each pixel independently: a maximum value means fully opaque, zero means fully transparent, and intermediate values produce semi-transparency. Like its three-channel counterpart, RGBA files require the image dimensions and bit depth to be specified externally since the raw data stream contains no metadata. The format supports 8-bit (four bytes per pixel, 32-bit total), 16-bit, and floating-point channel depths. In compositing workflows, the alpha channel enables layering operations where foreground elements are blended over backgrounds according to their per-pixel opacity — the mathematical foundation for all modern image compositing, described by Porter and Duff in their seminal 1984 paper on digital compositing. One advantage is direct framebuffer compatibility: modern GPU hardware natively processes 32-bit RGBA pixels, so raw RGBA data can be uploaded to texture memory or written from render targets without any format conversion, critical for real-time graphics applications and game engines. The format's simplicity in representing transparent images provides another practical benefit — scientific visualization, medical imaging, and overlay rendering can produce raw RGBA output that any downstream tool can consume without needing a common container format. RGBA files are handled by ImageMagick, FFmpeg, and various graphics and compositing tools.