Graphics File Formats(Windows的.BMP .CUR .ICO文件的格式，有范例)

value meaning

0 end of line.
1 end of bitmap.
2 delta. the two bytes following the escape contain unsigned values
indicating the horizontal and vertical offset of the next pixel from the
current position.

absolute mode is signaled by the first byte set to zero and the second byte
set to a value between 0x03 and 0xff. in absolute mode, the second byte
represents the number of bytes that follow, each of which contains the color
index of a single pixel. when the second byte is set to 2 or less, the escape
has the same meaning as in encoded mode. in absolute mode, each run must be
aligned on a word boundary. the following example shows the hexadecimal
values of an 8-bit compressed bitmap:

03 04 05 06 00 03 45 56 67 00 02 78 00 02 05 01
02 78 00 00 09 1e 00 01

this bitmap would expand as follows (two-digit values represent a color index
for a single pixel):

04 04 04
06 06 06 06 06
45 56 67
78 78
move current position 5 right and 1 down
78 78
end of line
1e 1e 1e 1e 1e 1e 1e 1e 1e
end of rle bitmap

bi_rle4

when the bicompression member is set to bi_rle4, the bitmap is compressed
using a run-length encoding (rle) format for a 4-bit bitmap, which also uses
encoded and absolute modes. in encoded mode, the first byte of the pair
contains the number of pixels to be drawn using the color indexes in the
second byte. the second byte contains two color indexes, one in its
high-order nibble (that is, its low-order four bits) and one in its low-order
nibble. the first of the pixels is drawn using the color specified by the
high-order nibble, the second is drawn using the color in the low-order
nibble, the third is drawn with the color in the high-order nibble, and so
on, until all the pixels specified by the first byte have been drawn. in
absolute mode, the first byte contains zero, the second byte contains the
number of color indexes that follow, and subsequent bytes contain color
indexes in their high- and low-order nibbles, one color index for each pixel.
in absolute mode, each run must be aligned on a word boundary. the
end-of-line, end-of-bitmap, and delta escapes also apply to bi_rle4.

the following example shows the hexadecimal values of a 4-bit compressed
bitmap:

03 04 05 06 00 06 45 56 67 00 04 78 00 02 05 01
04 78 00 00 09 1e 00 01

this bitmap would expand as follows (single-digit values represent a color
index for a single pixel):

0 4 0
0 6 0 6 0
4 5 5 6 6 7
7 8 7 8
move current position 5 right and 1 down
7 8 7 8
end of line
1 e 1 e 1 e 1 e 1
end of rle bitmap

see also

bitmapinfo

==============================================================================
rgbquad (3.0)

typedef struct tagrgbquad { /* rgbq */
byte rgbblue;
byte rgbgreen;
byte rgbred;
byte rgbreserved;
} rgbquad;

the rgbquad structure describes a color consisting of relative intensities of
red, green, and blue. the bmicolors member of the bitmapinfo structure
consists of an array of rgbquad structures.

member description

rgbblue specifies the intensity of blue in the color.
rgbgreenspecifies the intensity of green in the color.