Converting Truevision VDA to PNG: Historical TARGA Video Graphics Decoding

In 1984, AT&T and Truevision introduced the world's first truecolor video capture and display hardware for IBM PC compatibles. Alongside the famous TARGA (Truevision Advanced Raster Graphics Adapter) standard, Truevision shipped specialized imaging boards named VDA (Video Display Adapter), ICB (Image Capture Board), and VST (Video Solid State).

Each hardware product used its own file extension (.vda, .icb, .vst), though they all conformed to the foundational 18-byte Truevision binary header specification. Because modern photo viewers and web browsers rarely recognize the .vda or .icb extensions, converting them into standard transparent 32-bit RGBA PNG files is critical for retro preservation and game modding.

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1. The Truevision 18-Byte Header Specification

All Truevision raster formats share an identical 18-byte header:

| Offset | Field | Description | |---|---|---| | 0x00 | ID Length | Length of arbitrary text metadata preceding the image pixels | | 0x01 | Color Map Type | 0 = No palette, 1 = Indexed color palette present | | 0x02 | Image Type | 1 = Colormapped, 2 = Truecolor RGB, 3 = Grayscale, 9/10/11 = RLE compressed | | 0x03 | Color Map Spec | 5 bytes: start index, palette length, and palette bit depth | | 0x08 | Image Spec | 10 bytes: X/Y origin, width, height, pixel depth, and image descriptor |

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2. Supported Color Depths and Orientations

Truevision images store pixels in little-endian order across diverse color configurations:

1. 8-bit Indexed: 256 color map palette entries in 15-bit, 24-bit, or 32-bit formats.
2. 15-bit & 16-bit Highcolor: 5 bits per RGB component plus 1 overlay or alpha bit.
3. 24-bit Truecolor: Raw Blue-Green-Red (BGR) byte triplets.
4. 32-bit RGBA: BGR channels accompanied by an 8-bit linear alpha channel.

The image descriptor byte at offset 17 flags whether scanlines are ordered bottom-up (the traditional Truevision hardware convention) or top-down. convrtr transparently flips bottom-up rasters to match standard PNG scanline coordinates.

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3. Run-Length Encoding (RLE) Decompression

For compressed types (9, 10, and 11), pixels are encoded using byte-oriented packets:

• Run-Length Packet (Bit 7 = 1): Repeat the following pixel (count & 0x7F) + 1 times.
• Raw Packet (Bit 7 = 0): Read the next count + 1 distinct pixels uncompressed.

convrtr inflates RLE runs directly into a continuous 32-bit RGBA pixel array before encoding with its pure in-browser PNG encoder.

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4. Zero-Server Private Conversion

All Truevision header inspection, color map indexing, RLE decompression, and PNG compression occur 100% locally within your browser sandbox. No graphics or sensitive video frames ever leave your device.