TGA codec support

This document defines the implemented boundary of the first-party TGA codec.

Decode

• Uncompressed and RLE color-mapped images, types 1 and 9
• Uncompressed and RLE truecolor images, types 2 and 10
• Uncompressed and RLE grayscale images, types 3 and 11
• 8-bit and 16-bit color-map indices with nonzero color-map origins
• 15-bit RGB555 and 16-bit RGB5551
• 24-bit BGR and 32-bit BGRA
• 8-bit grayscale
• Top-left, top-right, bottom-left, and bottom-right origins
• Image ID metadata
• Region decode with bounded row output
• Interleaved two-way or four-way raster storage
• Extension-area and developer-area metadata

Encode

• Deterministic 24-bit RGB and 32-bit RGBA
• Uncompressed output
• Optional raw-packet and run-packet RLE
• TGA 2.0 footer signature
• Indexed output

Validation

• Dimension, palette extent, palette index, attribute-bit, packet-length, and truncation checks
• FFmpeg RLE interoperability fixture derived from a CC0 source image
• Checksum-pinned optional historical compatibility downloads kept outside the repository