Sustainability of Digital Formats
Planning for Library of Congress Collections
Sustainability of Digital Formats
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| Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact | |
| Full name | Truevision TGA File format, version 2.0 Truevision Advanced Raster Graphics Adapter (TARGA) |
| Description | A simple raster format for individual images first established by Truevision, Inc. in 1984 and extended in 1989. Designed for use on systems that use MS-DOS color applications, TGA is the native format of Truevision's TARGA boards, which were some of the first graphic cards for IBM-compatible PCs to support truecolor display (most often defined as 24-bit RGB color encoding). TGA supports mapped/indexed color and RGB color, with additional support for transparency information (sometimes referred to as alpha channel, as in RGBA color space). Transparency information permits images to be superimposed over other data, e.g., additional images, text layouts, or video, and permits effects like cross-fading between graphic images and video, etc. TGA images may be encoded at 8, 16, 24, or 32 bits per pixel (as mapped/indexed color, RGB, or RGBA). TGA supported 24-bit color before such support was available in the TIFF format, and this helped establish the format's popularity during the 1980s. Features added in version 2.0 include specification of pixel aspect ratio (providing more explicit support for square and non-square pixels), color correction tables, an embedded thumbnail image (termed postage-stamp in the standard), and some very basic metadata elements (such as author, software, date/timestamp, job number, comments). A developer area provided a mechanism for including additional information. |
| Production phase | Most often an initial-state or middle-state format. |
| Relationship to other formats | |
| Has earlier version | TGA_1 Truevision TGA, version 1.0 |
| LC experience or existing holdings | None. |
| LC preference | Not a preferred format. Lossless transformation to TIFF_6 recommended for final-state works. |
| Disclosure | Proprietary. Truevision used to make the specification available. Truevision was acquired by Pinnacle Systems in 1999. The TGA specification does not seem to be available from the Pinnacle Systems website. |
| Documentation | The specification Truevision TGA, File Format Specification, Version 2.0
is available in various forms on the Internet, e.g., Truevision TGA, File Format Specification, Version 2.0 as PDF. [http://www.dca.fee.unicamp.br/~martino/disciplinas/ea978/tgaffs.pdf] |
| Adoption | This format was widely used by graphics specialists before most personal computers had graphics displays. As an industry standard, it is not as widely supported as PCX or TIFF formats. TGA (versions 1.0 and 2.0) have retained popularity for computer graphics professionals and video-game developers as a simple format that supports high bit-depth (up to 32 bits per pixel) and transparency. It is widely supported by high-end paint programs and ray tracing packages. Used in particular for "texture" files used for image composition and 3D-rendering techniques. |
| Licensing and patent claims | Technically proprietary, but not exploited. |
| Transparency | Simple bitstream encoding is very transparent. Optional compression using run length encoding (RLE) is susceptible to reverse engineering without sophistication. |
| Self-documentation | Minimal support for embedded metadata. |
| External dependencies | None |
| Technical protection considerations | None |
| Normal rendering for still images | Good support. |
| Clarity (support for high image resolution) | Support for images with high spatial resolution. Support for RGB (plus transparency) color space or mapped (indexed) color and bit depth of 8, 16, 24, or 32 bits per pixel. |
| Color maintenance | Designed primarily for use on PC video displays using RGB colorspace. No support for ICC color profiles. |
| Support for graphic effects and typography | No support for vector graphics. |
| Functionality beyond normal image rendering | Support for transparency. |
| Tag type | Value | Note |
| Filename Extension | tga | Recommended in TGA version 2 specification. |
| Mac OS file type | TPIC | Documented in TGA version 2 specification. |
| Signature in TGA footer | ASCII: TRUEVISION-XFILE | In TGA version 2.0 files, this signature is in bytes 8-23 of the TGA footer, which comprises the last 26 bytes in the file. |
| General | |
| History | Truevision defined the first version of its TGA file format in 1984 for use with its first videographics products, including video boards for PC displays. In 1989, Truevision introduced TGA version 2.0. The new version was designed to allow software that worked with version 1.0 to work with version 2.0 images (ignoring the added functionality). However, neither of the two versions is a strict subtype of the other. |
URLs
• Truevision TGA, File Format Specification, Version 2.0 as PDF. [http://www.dca.fee.unicamp.br/~martino/disciplinas/ea978/tgaffs.pdf]
Print
URLs
• http://www.gamers.org/dEngine/quake3/TGA.txt
• http://www.dcs.ed.ac.uk/home/mxr/gfx/2d/TGA.txt
• http://astronomy.swin.edu.au/~pbourke/dataformats/tga/
• http://netghost.narod.ru/gff/
Print
• Murray, James D. and William vanRyper. Encyclopedia of Graphics File Formats, Second Edition. Sebastopol, CA. : O'Reilly & Associates, 1994. Includes CD-ROM with complete text of book, and copies of several file format specifications.
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