TGA 文件解析

TGA File Format

A .tga file is commonly used graphic file format that is easy to read and write.

Format Notes

• TGA files support 8,15,16,24,32 bit depths.
• 8 bit can be grey scale
• Runlength compression
• Additional Footer information optional x/y origin relative to lower left with origin in lower left
•  descriptor: 00vhaaaa
  • h horizontal flip
  • v vertical flip
  • a alpha bits

File Header (18 bytes)

typedef struct

{

    byte  identsize;          // size of ID field that follows 18 byte header (0 usually)                                        

    byte  colourmaptype;      // type of colour map 0=none, 1=has palette

    byte  imagetype;          // type of image 0=none,1=indexed,2=rgb, 3=grey,+8=rle packed

 

    short colourmapstart;     // first colour map entry in palette

    short colourmaplength;    // number of colours in palette

    byte  colourmapbits;      // number of bits per palette entry 15,16,24,32

 

    short xstart;             // image x origin

    short ystart;             // image y origin

    short width;              // image width in pixels

    short height;             // image height in pixels

    byte  bits;               // image bits per pixel 8,16,24,32

    byte  descriptor;         // image descriptor bits (vh flip bits)

   

    // pixel data follows header

   

} TGA_HEADER

 

 

Example File Header

Here is the header of a 32 bit image with dimensions 1920x1080. Note that these hex rows are 18 bytes so the entire TGA header is on the top row.  Also notice that even though the columapbits is set to 32 the bits is set to 24, thus the pixel data is actually 24 bpp.

 

00000000 00 00 02 00 00 00 00 20 00 00 00 00 80 07 38 04 18 00     ....... ......8...

00000018 31 52 41 18 52 10 10 6A 18 31 6A 5A 39 73 5A 41 73 6A      1RA.R..j.1jZ9sZAsj

00000036 52 73 7B 52 73 9C 39 5A 7B 31 4A 6A 31 4A 73 41 6A 94     Rs{Rs.9Z{1Jj1JsAj.

00000054 52 73 A4 29 20 18 20 18 10 10 10 10 18 18 18 29 29 29      Rs.) . ........)))

00000072 20 29 29 29 31 31 29 31 31 29 39 39 39 39 39 31 31 39       )))11)11)99999119

00000090 20 31 31 39 39 39 31 41 41 31 39 41 31 39 39 31 39 39      119991AA19A199199

 

 

 

后记：

         TGA是一种图片格式，使用工具ACDSee或者photoshop都可以打开，也可以另存为tga后缀的文件。

         一般去掉18 bytes的文件头，就是数据内容。使用UE可以比较，数据内容都是一模一样的。

 

 

详细格式可参考以下网址：

http://en.wikipedia.org/wiki/Truevision_TGA

TGA spec请参考如下网址：

http://www.dca.fee.unicamp.br/~martino/disciplinas/ea978/tgaffs.pdf