TGA

Revision as of 20:05, 19 September 2016

TGA (Targa) is a raster image file format developed by Truevision, Inc. (then named EPICenter) in 1984. Designed for use with MS-DOS color applications, TGA is the native format of Truevision's TARGA (Truevision Advanced Raster Graphics Adapter) boards, which were some of the first graphic cards for IBM-compatible PCs to support 24-bit RGB color encoding (sometimes termed truecolor).

Most TGA files are quite simple, but the format has the potential to be fairly complex.

TGA images are normally either uncompressed, or compressed with run-length encoding. Additional compression schemes may exist.

Format details

Files begin with an 18-byte fixed header, sometimes followed by other segments, followed by the pixel data. After the pixel data, there may be additional data elements referred to by an optional 26-byte file footer.

Variant formats

Ssome Truevision products used their own variant of TGA, or maybe just TGA with a different filename extension:

• .icb (Image Capture Board)
• .vda (Video Display Adapter)
• .vst (Vista)

Information about these formats is hard to find.

VST

XnView is capable of reading and writing VST files. It seems that they have a 36(?)-byte header, with the signature "IGCH" at offset 20.

Identification

TGA files have no signature at the beginning of the file. They can be identified fairly reliably by testing whether the first 18 bytes have valid values for TGA format, but that is nontrivial.

Some, but not all, TGA files have a signature at the end of the file. In that case, the last 18 bytes of the file are the ASCII characters "TRUEVISION-XFILE.", followed by a NUL byte (0x00).

Versions

The first TGA format is now known as Original TGA Format, or (informally) TGA Version 1. It is characterized by the lack of a New TGA Format signature.

New TGA Format, or TGA Version 2.0, was released in 1989. It is characterized by a footer with a "TRUEVISION-XFILE" signature. It adds an optional "Extension Area" segment, with many standard metadata fields.

It also adds an optional "Developer Area" segment, which supports arbitrary custom data. A custom data item is tagged with a 16-bit integer identifier, similar to a TIFF tag. There does not appear to be any published list of TGA tags, though tag 20 seems to be used for Photoshop Image Resources.

Specifications

• Truevision TGA File Format Specification, Version 2.0: PostScript · PDF · HTML
• Information extracted by Martin Reddy from Appendix C of the Truevision Technical Guide
• Another copy of the file
• Picture format docs (of a number of formats including this one)

Software

TGA is widely supported. Software listed here has been arbitrarily selected.

• Netpbm: pamtotga, tgatoppm
• ImageMagick
• Libtga

Sample files

• http://www.fileformat.info/format/tga/sample/index.htm
• http://samples.libav.org/image-samples/TGA/
• http://links.uwaterloo.ca/Repository/TGA/
• http://www.virtualservidores.com/cstrike/gfx/env/
• tombexcavator samples

Links

• Truevision TGA: Wikipedia
• TGA File Format Summary, from the Encyclopedia of Graphics File Formats
• Creating TGA Image files By Paul Bourke, 1996.
• TGA format chart