File structure
The keywords in the tiff file are: file header, file directory, directory entry.
File header
The file header is usually
8Byte 0-1B: 49 49 or 4D 4D, the former means small byte first, the latter means big byte first
2-3B: generally 42, it is the flag bit
4-7B: the first file directory Must be an integer multiple of 2
File Directory
0-1B: The number of directory items contained in the file directory
Starting from 2B: directory items, each directory item accounts for 12B and
last 4B: the offset of the next file directory, 0 means no next
Directory entry
0-1B: label number
2-3B: data type of the directory item
4-7B: number of data
8-11B: offset of the variable value corresponding to the label number to the beginning of the file, if not more than 4 bytes, write in Here
analysis
Using the drawing software that comes with Windows, I made a pure black image of 11 * 10 pixels. Open it with a binary editor as follows.
00-01 is 49 49. The small byte is in the front, and 04-07 is 28 00 00 00 indicates the first The file directory is 28 bytes, and the 28-29 bytes are 0F, indicating that there are 15 directory entries, a total of 180 bytes, starting from 2A and ending at DE. The
data types correspond to the following
- 0001Byte
- 0002ASCII
- 0003integer
- 0004long
- 0005rational
The meaning of the label number is as follows
: 0100: image width; 0101: image height
0102: color depth; 0103: whether the image data is compressed
0106: whether the image is expressed in reverse color
0111: the offset of the image data from the beginning of the file
0117: data bytes Total number, if it is not even, 0 will be added.
011A: Horizontal resolution offset
011B: Vertical resolution offset
Analyze the image.
Directory item 1: Tag 00FE long does not know what
2: tag 0100, long, 1, 00 00 00 0B, width
3: tag 0101, long, 1, 00 00 00 0A, height
4 : Label 0102, integer, 3, E2 represents the offset, E2-E8 bytes, get 00 08 00 08 00 08, the length of the directory entry is greater than 2, expressed as true color
5: 0103, integer, 1, 00 05, indicates that the image is compressed
6: 0106, integer, 1, 00 02, indicates that it is not the reverse color
7: 0111, long, 1, 00 00 00 08, image data offset
8: 0115, integer, 1 , 00 03, the number of samples per pixel
9: 0116, long, 1, 00 00 00 0A, equal to the image height
10: 0117, long, 1, 00 00 00 20, the image data is 20 bytes long
11: 011A , rational, 1, 00 E8, horizontal resolution offset
12: 011B, rational, 1, 00 F0, vertical resolution offset
13: 011c, integer, 1, 00 01, storage format
14: 0128 , Integer, 1, 0002, unit of measurement, 0002 means the unit is
15: 013D per pixel per foot , integer, 1, 00 02, the directory entry represents the mathematical operation before encoding
where the resolution information occupies 8 bytes, before 4 Represents the numerator, the last four represent the denominator
