TGA 文件格式标准

Truevision TGAª

FILE FORMAT SPECIFICATION

Version 2.0

Document prepared by:

Truevision, Inc.

7340 Shadeland Station

Indianapolis, IN 46256-3925

800-729-2656 - phone

317-576-7700 - FAX

TrueVista is a registered trademark of Truevision, Inc.

ATVista is a registered trademark of Truevision, Inc.

TGA is a trademark of Truevision, Inc.

This manual and the enclosed software were prepared by Truevision, Inc. While the authors and program

developers have taken reasonable care in preparing this manual to assure accuracy, the authors assume no

liability resulting from any inaccuracy or omissions contained in them or from the use of the information or

programs contained herein.

DEFINITIONS .............................................................................................................................2

TGA FILE FORMAT SPECIFICATION........................................................................................4

TGA FILE HEADER....................................................................................................................6

EXTENSION AREA.........................................................................13

TGA FILE FOOTER.........................................................................19

IMAGE TYPES ...............................................................................21

RUN-LENGTH ENCODING OF IMAGES........................................24

INTRODUCTION

The success of the TGAª File Format for storing color images can be attributed to its ease of use, the small

amount of program memory needed to parse the file, and the fact that it was the first true-color file format

widely available. Truevision¨ defined the TGA file format in 1984 for use with its first videographics

products. Since then, it has been estimated that today over 80 percent of the color images stored on hard

drives employ some variation of the TGA file format. Many government offices, corporations, service

bureaus, production shops and nearly all Truevision developers have standardized on the TGA format as a

The extensions are optional and will have no impact on existing packages (assuming the packages followed

the original TGA File Format guidelines). In particular, the new TGA File Format addresses the following

DEFINITIONS

Throughout this document, we will be using the terms Pseudo-Color, True-Color and Direct-Color.

These terms are defined as follows:

Pseudo-Color

True-Color

Direct-Color

The TrueVista¨ (ATVista and NuVista) videographics cards can be programmed to accept images which

are Pseudo-Color, True-Color and Direct-Color. When they are functioning in any of the Linked Modes,

they are said to be acting as Pseudo-Color devices. When they are configured for any of the Independent

they are said to be acting as True-Color devices.

The VDA, VDA/D, TARGA M8 and HR can only be used as Pseudo-Color devices.

The ICB, TARGA 16, 24 and 32 can only be used as True-Color devices.

Long

= 32 bit value

Bit Numbering (for diagrams in this document)