.TGA

Introduction

TGA, also called TARGA, is a raster image format made by Truevision in the 1980s for its TARGA and VISTA graphics cards. It stores palette, truecolour or greyscale images, either raw or with simple run-length compression.

Its simple layout and support for an alpha channel made it a long-standing choice for textures in games and 3D software, where it is still common.

Structure

A TGA file has no signature at the start. It opens with an 18-byte little-endian header: the length of an optional image ID, whether there is a colour map, the image type, the colour map's layout, then the image's origin, width, height, bits per pixel and a descriptor byte. The descriptor gives the number of alpha bits and whether rows run from the bottom up or the top down.

The image type is 1 for colour-mapped, 2 for truecolour and 3 for greyscale, with 8 added for the run-length encoded versions (9, 10 and 11). Version 2.0 of the format adds an extension area, a developer area and a 26-byte footer that ends with the text TRUEVISION-XFILE. and a zero byte.

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