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| 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. |
| | | |
--------------------------------------------------------------------------------</pre>
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