TGA
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Truevision TGA, often referred to as TARGA, is a raster graphics file format. TGA is an initialism for Truevision Graphics Adapter.
File format[edit | edit source]
Header[edit | edit source]
All Targa formats are identified by a Data Type field, which is a one byte binary integer located in byte three of the file. These data types are:
0 - No image data included.
1 - Uncompressed, color-mapped images.
2 - Uncompressed, RGB images.
3 - Uncompressed, black and white images.
9 - Runlength encoded color-mapped images.
10 - Runlength encoded RGB images.
11 - Compressed, black and white images.
32 - Compressed color-mapped data, using Huffman, Delta, and
runlength encoding.
33 - Compressed color-mapped data, using Huffman, Delta, and
runlength encoding. 4-pass quadtree-type process.
The bitsperpixel specifies the size of each colour value. When 24 or 32 the normal conventions apply. For 16 bits each colour component is stored as 5 bits and the remaining bit is a binary alpha value. The colour components are converted into single byte components by simply shifting each component up by 3 bits (multiply by 8).
DATA TYPE 1: Color-mapped images ________________________________________________________________________________ | Offset | Length | Description | |--------|--------|------------------------------------------------------------| | 0 | 1 | Number of Characters in Identification Field. | | | | | | | | This field is a one-byte unsigned integer, specifying | | | | the length of the Image Identification Field. Its range | | | | is 0 to 255. A value of 0 means that no Image | | | | Identification Field is included. | |--------|--------|------------------------------------------------------------| | 1 | 1 | Color Map Type. | | | | | | | | This field contains a binary 1 for Data Type 1 images. | |--------|--------|------------------------------------------------------------| | 2 | 1 | Image Type Code. | | | | | | | | This field will always contain a binary 1. | | | | ( That's what makes it Data Type 1 ). | |--------|--------|------------------------------------------------------------| | 3 | 5 | Color Map Specification. | | | | | | 3 | 2 | Color Map Origin. | | | | Integer ( lo-hi ) index of first color map entry. | | 5 | 2 | Color Map Length. | | | | Integer ( lo-hi ) count of color map entries. | | 7 | 1 | Color Map Entry Size. | | | | Number of bits in each color map entry. 16 for | | | | the Targa 16, 24 for the Targa 24, 32 for the Targa 32. | |--------|--------|------------------------------------------------------------| | 8 | 10 | Image Specification. | | | | | | 8 | 2 | X Origin of Image. | | | | Integer ( lo-hi ) X coordinate of the lower left corner | | | | of the image. | | 10 | 2 | Y Origin of Image. | | | | Integer ( lo-hi ) Y coordinate of the lower left corner | | | | of the image. | | 12 | 2 | Width of Image. | | | | Integer ( lo-hi ) width of the image in pixels. | | 14 | 2 | Height of Image. | | | | Integer ( lo-hi ) height of the image in pixels. | | 16 | 1 | Image Pixel Size. | | | | Number of bits in a stored pixel index. | | 17 | 1 | Image Descriptor Byte. | | | | Bits 3-0 - number of attribute bits associated with each | | | | pixel. | | | | Bit 4 - reserved. Must be set to 0. | | | | Bit 5 - screen origin bit. | | | | 0 = Origin in lower left-hand corner. | | | | 1 = Origin in upper left-hand corner. | | | | Must be 0 for Truevision images. | | | | Bits 7-6 - Data storage interleaving flag. | | | | 00 = non-interleaved. | | | | 01 = two-way (even/odd) interleaving. | | | | 10 = four way interleaving. | | | | 11 = reserved. | | | | This entire byte should be set to 0. Don't ask me. | |--------|--------|------------------------------------------------------------| | 18 | varies | Image Identification Field. | | | | | | | | Contains a free-form identification field of the length | | | | specified in byte 1 of the image record. It's usually | | | | omitted ( length in byte 1 = 0 ), but can be up to 255 | | | | characters. If more identification information is | | | | required, it can be stored after the image data. | |--------|--------|------------------------------------------------------------| | varies | varies | Color map data. | | | | | | | | The offset is determined by the size of the Image | | | | Identification Field. The length is determined by | | | | the Color Map Specification, which describes the | | | | size of each entry and the number of entries. | | | | Each color map entry is 2, 3, or 4 bytes. | | | | Unused bits are assumed to specify attribute bits. | | | | The 4 byte entry contains 1 byte for blue, 1 byte | | | | for green, 1 byte for red, and 1 byte of attribute | | | | information, in that order. | | | | The 3 byte entry contains 1 byte each of blue, green, | | | | and red. | | | | The 2 byte entry is broken down as follows: | | | | ARRRRRGG GGGBBBBB, where each letter represents a bit. | | | | But, because of the lo-hi storage order, the first byte | | | | coming from the file will actually be GGGBBBBB, and the | | | | second will be ARRRRRGG. "A" represents an attribute bit. | |--------|--------|------------------------------------------------------------| | varies | varies | Image Data Field. | | | | | | | | This field specifies (width) x (height) color map | | | | indices. Each index is stored as an integral number | | | | of bytes (typically 1 or 2). All fields are unsigned. | | | | The low-order byte of a two-byte field is stored first. | -------------------------------------------------------------------------------- DATA TYPE 2: Unmapped RGB ________________________________________________________________________________ | Offset | Length | Description | |--------|--------|------------------------------------------------------------| | 0 | 1 | Number of Characters in Identification Field. | | | | | | | | This field is a one-byte unsigned integer, specifying | | | | the length of the Image Identification Field. Its value | | | | is 0 to 255. A value of 0 means that no Image | | | | Identification Field is included. | |--------|--------|------------------------------------------------------------| | 1 | 1 | Color Map Type. | | | | | | | | This field contains either 0 or 1. 0 means no color map | | | | is included. 1 means a color map is included, but since | | | | this is an unmapped image it is usually ignored. TIPS | | | | ( a Targa paint system ) will set the border color | | | | the first map color if it is present. | |--------|--------|------------------------------------------------------------| | 2 | 1 | Image Type Code. | | | | | | | | This field will always contain a binary 2. | | | | ( That's what makes it Data Type 2 ). | |--------|--------|------------------------------------------------------------| | 3 | 5 | Color Map Specification. | | | | | | | | Ignored if Color Map Type is 0; otherwise, interpreted | | | | as follows: | | 3 | 2 | Color Map Origin. | | | | Integer ( lo-hi ) index of first color map entry. | | 5 | 2 | Color Map Length. | | | | Integer ( lo-hi ) count of color map entries. | | 7 | 1 | Color Map Entry Size. | | | | Number of bits in color map entry. 16 for the Targa 16, | | | | 24 for the Targa 24, 32 for the Targa 32. | |--------|--------|------------------------------------------------------------| | 8 | 10 | Image Specification. | | | | | | 8 | 2 | X Origin of Image. | | | | Integer ( lo-hi ) X coordinate of the lower left corner | | | | of the image. | | 10 | 2 | Y Origin of Image. | | | | Integer ( lo-hi ) Y coordinate of the lower left corner | | | | of the image. | | 12 | 2 | Width of Image. | | | | Integer ( lo-hi ) width of the image in pixels. | | 14 | 2 | Height of Image. | | | | Integer ( lo-hi ) height of the image in pixels. | | 16 | 1 | Image Pixel Size. | | | | Number of bits in a pixel. This is 16 for Targa 16, | | | | 24 for Targa 24, and .... well, you get the idea. | | 17 | 1 | Image Descriptor Byte. | | | | Bits 3-0 - number of attribute bits associated with each | | | | pixel. For the Targa 16, this would be 0 or | | | | 1. For the Targa 24, it should be 0. For | | | | Targa 32, it should be 8. | | | | Bit 4 - reserved. Must be set to 0. | | | | Bit 5 - screen origin bit. | | | | 0 = Origin in lower left-hand corner. | | | | 1 = Origin in upper left-hand corner. | | | | Must be 0 for Truevision images. | | | | Bits 7-6 - Data storage interleaving flag. | | | | 00 = non-interleaved. | | | | 01 = two-way (even/odd) interleaving. | | | | 10 = four way interleaving. | | | | 11 = reserved. | |--------|--------|------------------------------------------------------------| | 18 | varies | Image Identification Field. | | | | | | | | Contains a free-form identification field of the length | | | | specified in byte 1 of the image record. It's usually | | | | omitted ( length in byte 1 = 0 ), but can be up to 255 | | | | characters. If more identification information is | | | | required, it can be stored after the image data. | |--------|--------|------------------------------------------------------------| | varies | varies | Color map data. | | | | | | | | If the Color Map Type is 0, this field doesn't exist. | | | | Otherwise, just read past it to get to the image. | | | | The Color Map Specification describes the size of each | | | | entry, and the number of entries you'll have to skip. | | | | Each color map entry is 2, 3, or 4 bytes. | |--------|--------|------------------------------------------------------------| | varies | varies | Image Data Field. | | | | | | | | This field specifies (width) x (height) pixels. Each | | | | pixel specifies an RGB color value, which is stored as | | | | an integral number of bytes. | | | | The 2 byte entry is broken down as follows: | | | | ARRRRRGG GGGBBBBB, where each letter represents a bit. | | | | But, because of the lo-hi storage order, the first byte | | | | coming from the file will actually be GGGBBBBB, and the | | | | second will be ARRRRRGG. "A" represents an attribute bit. | | | | The 3 byte entry contains 1 byte each of blue, green, | | | | and red. | | | | The 4 byte entry contains 1 byte each of blue, green, | | | | red, and attribute. For faster speed (because of the | | | | hardware of the Targa board itself), Targa 24 images are | | | | sometimes stored as Targa 32 images. | -------------------------------------------------------------------------------- DATA TYPE 9: Run Length Encoded, color-mapped images -------------------------------------------------------------------------------- | Offset | Length | Description | |--------|--------|------------------------------------------------------------| | 0 | 1 | Number of Characters in Identification Field. | | | | | | | | This field is a one-byte unsigned integer, specifying | | | | the length of the Image Identification Field. Its value | | | | is 0 to 255. A value of 0 means that no Image | | | | Identification Field is included. | |--------|--------|------------------------------------------------------------| | 1 | 1 | Color Map Type. | | | | | | | | This field is always 1 for color-mapped images. | |--------|--------|------------------------------------------------------------| | 2 | 1 | Image Type Code. | | | | | | | | A binary 9 for this data type. | |--------|--------|------------------------------------------------------------| | 3 | 5 | Color Map Specification. | | | | | | 3 | 2 | Color Map Origin. | | | | Integer ( lo-hi ) index of first color map entry. | | 5 | 2 | Color Map Length. | | | | Integer ( lo-hi ) count of color map entries. | | 7 | 1 | Color Map Entry Size. | | | | Number of bits in each color map entry. 16 for the | | | | Targa 16, 24 for the Targa 24, 32 for the Targa 32. | |--------|--------|------------------------------------------------------------| | 8 | 10 | Image Specification. | | | | | | 8 | 2 | X Origin of Image. | | | | Integer ( lo-hi ) X coordinate of the lower left corner | | | | of the image. | | 10 | 2 | Y Origin of Image. | | | | Integer ( lo-hi ) Y coordinate of the lower left corner | | | | of the image. | | 12 | 2 | Width of Image. | | | | Integer ( lo-hi ) width of the image in pixels. | | 14 | 2 | Height of Image. | | | | Integer ( lo-hi ) height of the image in pixels. | | 16 | 1 | Image Pixel Size. | | | | Number of bits in a pixel. This is 16 for Targa 16, | | | | 24 for Targa 24, and .... well, you get the idea. | | 17 | 1 | Image Descriptor Byte. | | | | Bits 3-0 - number of attribute bits associated with each | | | | pixel. For the Targa 16, this would be 0 or | | | | 1. For the Targa 24, it should be 0. For the | | | | Targa 32, it should be 8. | | | | Bit 4 - reserved. Must be set to 0. | | | | Bit 5 - screen origin bit. | | | | 0 = Origin in lower left-hand corner. | | | | 1 = Origin in upper left-hand corner. | | | | Must be 0 for Truevision images. | | | | Bits 7-6 - Data storage interleaving flag. | | | | 00 = non-interleaved. | | | | 01 = two-way (even/odd) interleaving. | | | | 10 = four way interleaving. | | | | 11 = reserved. | |--------|--------|------------------------------------------------------------| | 18 | varies | Image Identification Field. | | | | | | | | Contains a free-form identification field of the length | | | | specified in byte 1 of the image record. It's usually | | | | omitted ( length in byte 1 = 0 ), but can be up to 255 | | | | characters. If more identification information is | | | | required, it can be stored after the image data. | |--------|--------|------------------------------------------------------------| | varies | varies | Color map data. | | | | | | | | The offset is determined by the size of the Image | | | | Identification Field. The length is determined by | | | | the Color Map Specification, which describes the | | | | size of each entry and the number of entries. | | | | Each color map entry is 2, 3, or 4 bytes. | | | | Unused bits are assumed to specify attribute bits. | | | | The 4 byte entry contains 1 byte for blue, 1 byte | | | | for green, 1 byte for red, and 1 byte of attribute | | | | information, in that order. | | | | The 3 byte entry contains 1 byte each of blue, green, | | | | and red. | | | | The 2 byte entry is broken down as follows: | | | | ARRRRRGG GGGBBBBB, where each letter represents a bit. | | | | But, because of the lo-hi storage order, the first byte | | | | coming from the file will actually be GGGBBBBB, and the | | | | second will be ARRRRRGG. "A" represents an attribute bit. | |--------|--------|------------------------------------------------------------| | varies | varies | Image Data Field. | | | | | | | | This field specifies (width) x (height) color map | | | | indices. The indices are stored in packets. There | | | | two types of packets: Run-length packets, and Raw | | | | packets. Both types of packets consist of a 1-byte | | | | header, identifying the type of packet and specifying a | | | | count, followed by a variable-length body. | | | | The high-order bit of the header is "1" for the | | | | run length packet, and "0" for the raw packet. | | | | | | | | For the run-length packet, the header consists of: | | | | __________________________________________________ | | | | | 1 bit | 7 bit repetition count minus 1. | | | | | | ID | Since the maximum value of this | | | | | | | field is 127, the largest possible | | | | | | | run size would be 128. | | | | | |-------|----------------------------------------| | | | | | 1 | C C C C C C C | | | | | -------------------------------------------------- | | | | | | | | For the raw packet, the header consists of: | | | | __________________________________________________ | | | | | 1 bit | 7 bit number of pixels minus 1. | | | | | | ID | Since the maximum value of this | | | | | | | field is 127, there can never be | | | | | | | more than 128 pixels per packet. | | | | | |-------|----------------------------------------| | | | | | 0 | N N N N N N N | | | | | -------------------------------------------------- | | | | | | | | For the run length packet, the header is followed by | | | | a single color index, which is assumed to be repeated | | | | the number of times specified in the header. The RLE | | | | packet may cross scan lines ( begin on one line and end | | | | on the next ). | | | | For the raw packet, the header is followed by the number | | | | of color indices specified in the header. The raw | | | | packet may cross scan lines ( begin on one line and end | | | | on the next ). | -------------------------------------------------------------------------------- DATA TYPE 10: Run Length Encoded, RGB images ________________________________________________________________________________ | Offset | Length | Description | |--------|--------|------------------------------------------------------------| | 0 | 1 | Number of Characters in Identification Field. | | | | | | | | This field is a one-byte unsigned integer, specifying | | | | the length of the Image Identification Field. Its range | | | | is 0 to 255. A value of 0 means that no Image | | | | Identification Field is included. | |--------|--------|------------------------------------------------------------| | 1 | 1 | Color Map Type. | | | | | | | | This field contains either 0 or 1. 0 means no color map | | | | is included. 1 means a color map is included, but since | | | | this is an unmapped image it is usually ignored. TIPS | | | | ( a Targa paint system ) will set the border color | | | | the first map color if it is present. Wowie zowie. | |--------|--------|------------------------------------------------------------| | 2 | 1 | Image Type Code. | | | | | | | | Binary 10 for this type of image. | |--------|--------|------------------------------------------------------------| | 3 | 5 | Color Map Specification. | | | | | | | | Ignored if Color Map Type is 0; otherwise, interpreted | | | | as follows: | | 3 | 2 | Color Map Origin. | | | | Integer ( lo-hi ) index of first color map entry. | | 5 | 2 | Color Map Length. | | | | Integer ( lo-hi ) count of color map entries. | | 7 | 1 | Color Map Entry Size. | | | | Number of bits in color map entry. This value is 16 for | | | | the Targa 16, 24 for the Targa 24, 32 for the Targa 32. | |--------|--------|------------------------------------------------------------| | 8 | 10 | Image Specification. | | | | | | 8 | 2 | X Origin of Image. | | | | Integer ( lo-hi ) X coordinate of the lower left corner | | | | of the image. | | 10 | 2 | Y Origin of Image. | | | | Integer ( lo-hi ) Y coordinate of the lower left corner | | | | of the image. | | 12 | 2 | Width of Image. | | | | Integer ( lo-hi ) width of the image in pixels. | | 14 | 2 | Height of Image. | | | | Integer ( lo-hi ) height of the image in pixels. | | 16 | 1 | Image Pixel Size. | | | | Number of bits in a pixel. This is 16 for Targa 16, | | | | 24 for Targa 24, and .... well, you get the idea. | | 17 | 1 | Image Descriptor Byte. | | | | Bits 3-0 - number of attribute bits associated with each | | | | pixel. For the Targa 16, this would be 0 or | | | | 1. For the Targa 24, it should be 0. For the | | | | Targa 32, it should be 8. | | | | Bit 4 - reserved. Must be set to 0. | | | | Bit 5 - screen origin bit. | | | | 0 = Origin in lower left-hand corner. | | | | 1 = Origin in upper left-hand corner. | | | | Must be 0 for Truevision images. | | | | Bits 7-6 - Data storage interleaving flag. | | | | 00 = non-interleaved. | | | | 01 = two-way (even/odd) interleaving. | | | | 10 = four way interleaving. | | | | 11 = reserved. | |--------|--------|------------------------------------------------------------| | 18 | varies | Image Identification Field. | | | | Contains a free-form identification field of the length | | | | specified in byte 1 of the image record. It's usually | | | | omitted ( length in byte 1 = 0 ), but can be up to 255 | | | | characters. If more identification information is | | | | required, it can be stored after the image data. | |--------|--------|------------------------------------------------------------| | varies | varies | Color map data. | | | | | | | | If the Color Map Type is 0, this field doesn't exist. | | | | Otherwise, just read past it to get to the image. | | | | The Color Map Specification, describes the size of each | | | | entry, and the number of entries you'll have to skip. | | | | Each color map entry is 2, 3, or 4 bytes. | |--------|--------|------------------------------------------------------------| | varies | varies | Image Data Field. | | | | | | | | This field specifies (width) x (height) pixels. The | | | | RGB color information for the pixels is stored in | | | | packets. There are two types of packets: Run-length | | | | encoded packets, and raw packets. Both have a 1-byte | | | | header, identifying the type of packet and specifying a | | | | count, followed by a variable-length body. | | | | The high-order bit of the header is "1" for the | | | | run length packet, and "0" for the raw packet. | | | | | | | | For the run-length packet, the header consists of: | | | | __________________________________________________ | | | | | 1 bit | 7 bit repetition count minus 1. | | | | | | ID | Since the maximum value of this | | | | | | | field is 127, the largest possible | | | | | | | run size would be 128. | | | | | |-------|----------------------------------------| | | | | | 1 | C C C C C C C | | | | | -------------------------------------------------- | | | | | | | | For the raw packet, the header consists of: | | | | __________________________________________________ | | | | | 1 bit | 7 bit number of pixels minus 1. | | | | | | ID | Since the maximum value of this | | | | | | | field is 127, there can never be | | | | | | | more than 128 pixels per packet. | | | | | |-------|----------------------------------------| | | | | | 0 | N N N N N N N | | | | | -------------------------------------------------- | | | | | | | | For the run length packet, the header is followed by | | | | a single color value, which is assumed to be repeated | | | | the number of times specified in the header. The | | | | packet may cross scan lines ( begin on one line and end | | | | on the next ). | | | | For the raw packet, the header is followed by | | | | the number of color values specified in the header. | | | | The color entries themselves are two bytes, three bytes, | | | | or four bytes ( for Targa 16, 24, and 32 ), and are | | | | broken down as follows: | | | | The 2 byte entry - | | | | ARRRRRGG GGGBBBBB, where each letter represents a bit. | | | | But, because of the lo-hi storage order, the first byte | | | | coming from the file will actually be GGGBBBBB, and the | | | | second will be ARRRRRGG. "A" represents an attribute bit. | | | | The 3 byte entry contains 1 byte each of blue, green, | | | | and red. | | | | The 4 byte entry contains 1 byte each of blue, green, | | | | red, and attribute. For faster speed (because of the | | | | hardware of the Targa board itself), Targa 24 image are | | | | sometimes stored as Targa 32 images. | --------------------------------------------------------------------------------
[edit | edit source]
If a TGA image contains a footer, the chances are that it is a TGA version 2 file. The footer is the final 26 bytes of the file, of which the last 18 are constant.
| Field no. | Length | Field | Description |
|---|---|---|---|
| 0 | 4 bytes | Extension offset | Offset in bytes from the beginning of the file |
| 4 | 4 bytes | Developer area offset | Offset in bytes from the beginning of the file |
| 8 | 18 bytes | Signature | Contains "TRUEVISION-XFILE. " |