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jasonsilvey
04-21-2001, 09:52 AM
How would i print out and describe the function of all the contents of the file header for a .bmp file that i have loaded up? I also have to determine the size of each header component, the offsets, file size and the dimensions of the image etc.

Zadkiel
04-21-2001, 01:45 PM
Here's all the info I could find.
typedef struct tagBITMAPINFOHEADER{ // bmih

DWORD biSize;
LONG biWidth;
LONG biHeight;
WORD biPlanes;
WORD biBitCount
DWORD biCompression;
DWORD biSizeImage;
LONG biXPelsPerMeter;
LONG biYPelsPerMeter;
DWORD biClrUsed;
DWORD biClrImportant;
} BITMAPINFOHEADER;


The BITMAPINFOHEADER structure contains information about the dimensions and color format of a device-independent bitmap (DIB).

Members

biSize

Specifies the number of bytes required by the structure.

biWidth

Specifies the width of the bitmap, in pixels.

biHeight

Specifies the height of the bitmap, in pixels. If biHeight is positive, the bitmap is a bottom-up DIB and its origin is the lower left corner. If biHeight is negative, the bitmap is a top-down DIB and its origin is the upper left corner.

biPlanes

Specifies the number of planes for the target device. This value must be set to 1.

biBitCount

Specifies the number of bits per pixel. This value must be 1, 4, 8, 16, 24, or 32.

biCompression

Specifies the type of compression for a compressed bottom-up bitmap (top-down DIBs cannot be compressed). It can be one of the following values:

Value Description
BI_RGB An uncompressed format.
BI_RLE8 A run-length encoded (RLE) format for bitmaps with 8 bits per pixel. The compression format is a two-byte format consisting of a count byte followed by a byte containing a color index. For more information, see the following Remarks section.
BI_RLE4 An RLE format for bitmaps with 4 bits per pixel. The compression format is a two-byte format consisting of a count byte followed by two word-length color indices. For more information, see the following Remarks section.
BI_BITFIELDS Specifies that the bitmap is not compressed and that the color table consists of three doubleword color masks that specify the red, green, and blue components, respectively, of each pixel. This is valid when used with 16- and 32-bits-per-pixel bitmaps.
biSizeImage

Specifies the size, in bytes, of the image. This may be set to 0 for BI_RGB bitmaps.

biXPelsPerMeter

Specifies the horizontal resolution, in pixels per meter, of the target device for the bitmap. An application can use this value to select a bitmap from a resource group that best matches the characteristics of the current device.

biYPelsPerMeter

Specifies the vertical resolution, in pixels per meter, of the target device for the bitmap.

biClrUsed

Specifies the number of color indices in the color table that are actually used by the bitmap. If this value is zero, the bitmap uses the maximum number of colors corresponding to the value of the biBitCount member for the compression mode specified by biCompression.
If biClrUsed is nonzero and the biBitCount member is less than 16, the biClrUsed member specifies the actual number of colors the graphics engine or device driver accesses. If biBitCount is 16 or greater, then biClrUsed member specifies the size of the color table used to optimize performance of Windows color palettes. If biBitCount equals 16 or 32, the optimal color palette starts immediately following the three doubleword masks.

If the bitmap is a packed bitmap (a bitmap in which the bitmap array immediately follows the BITMAPINFO header and which is referenced by a single pointer), the biClrUsed member must be either 0 or the actual size of the color table.

biClrImportant

Specifies the number of color indices that are considered important for displaying the bitmap. If this value is zero, all colors are important.

Remarks

The BITMAPINFO structure combines the BITMAPINFOHEADER structure and a color table to provide a complete definition of the dimensions and colors of a DIB. For more information about DIBs, see the description of the BITMAPINFO data structure.
An application should use the information stored in the biSize member to locate the color table in a BITMAPINFO structure, as follows:

pColor = ((LPSTR)pBitmapInfo +
(WORD)(pBitmapInfo->bmiHeader.biSize));


Windows supports formats for compressing bitmaps that define their colors with eight or four bits per pixel. Compression reduces the disk and memory storage required for the bitmap. The following paragraphs describe these formats.
When the biCompression member is BI_RLE8, the bitmap is compressed by using a run-length encoding (RLE) format for an 8-bit bitmap. This format can be compressed in encoded or absolute modes. Both modes can occur anywhere in the same bitmap.

Encoded mode consists of two bytes: the first byte specifies the number of consecutive pixels to be drawn using the color index contained in the second byte. In addition, the first byte of the pair can be set to zero to indicate an escape that denotes an end of line, end of bitmap, or delta. The interpretation of the escape depends on the value of the second byte of the pair, which can be one of the following:

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 offsets of the next pixel from the current position.
In absolute mode, the first byte is zero and the second byte is a value in the range 03H through FFH. 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 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


When the biCompression member is BI_RLE4, the bitmap is compressed by using a run-length encoding 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 indices in the second byte. The second byte contains two color indices, one in its high-order four bits and one in its low-order four bits. The first of the pixels is drawn using the color specified by the high-order four bits, the second is drawn using the color in the low-order four bits, the third is drawn using the color in the high-order four bits, and so on, until all the pixels specified by the first byte have been drawn.

In absolute mode, the first byte is zero, the second byte contains the number of color indices that follow, and subsequent bytes contain color indices in their high- and low-order four bits, 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 described for BI_RLE8 also apply to BI_RLE4 compression.

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


If biHeight is negative, indicating a top-down DIB, biCompression must be either BI_RGB or BI_BITFIELDS. Top-down DIBs cannot be compressed.

Zadkiel
04-21-2001, 01:50 PM
And heres the INFO struct

typedef struct tagBITMAPINFO { // bmi

BITMAPINFOHEADER bmiHeader;
RGBQUAD bmiColors[1];
} BITMAPINFO;


The BITMAPINFO structure defines the dimensions and color information for a Windows device-independent bitmap (DIB).

Members

bmiHeader

Specifies a BITMAPINFOHEADER structure that contains information about the dimensions and color format of a DIB.

bmiColors

Specifies an array of RGBQUAD or doubleword data types that define the colors in the bitmap.

Remarks

A device-independent bitmap consists of two distinct parts: a BITMAPINFO structure describing the dimensions and colors of the bitmap, and an array of bytes defining the pixels of the bitmap. The bits in the array are packed together, but each scan line must be padded with zeroes to end on a LONG data-type boundary. If the height is positive, the bitmap is a bottom-up DIB and its origin is the lower left corner. If the height is negative, the bitmap is a top-down DIB and its origin is the upper left corner.

The biBitCount member of the BITMAPINFOHEADER structure determines the number of bits that define each pixel and the maximum number of colors in the bitmap. This member can be one of the following values:

Value Meaning
1 The bitmap is monochrome, and the bmiColors member contains two entries. Each bit in the bitmap array represents a pixel. If the bit is clear, the pixel is displayed with the color of the first entry in the bmiColors table; if the bit is set, the pixel has the color of the second entry in the table.
4 The bitmap has a maximum of 16 colors, and the bmiColors member contains up to 16 entries. Each pixel in the bitmap is represented by a 4-bit index into the color table. For example, if the first byte in the bitmap is 0x1F, the byte represents two pixels. The first pixel contains the color in the second table entry, and the second pixel contains the color in the sixteenth table entry.
8 The bitmap has a maximum of 256 colors, and the bmiColors member contains up to 256 entries. In this case, each byte in the array represents a single pixel.
16 The bitmap has a maximum of 2 (16) colors. If the biCompression member of the BITMAPINFOHEADER is BI_RGB, the bmiColors member is NULL. Each WORD in the bitmap array represents a single pixel. The relative intensities of red, green, and blue are represented with 5 bits for each color component. The value for blue is in the least significant 5 bits, followed by 5 bits each for green and red, respectively. The most significant bit is not used.If the biCompression member of the BITMAPINFOHEADER is BI_BITFIELDS, the bmiColors member contains three DWORD color masks that specify the red, green, and blue components, respectively, of each pixel. Each WORD in the bitmap array represents a single pixel.Windows NT: When the biCompression member is BI_BITFIELDS, bits set in each DWORD mask must be contiguous and should not overlap the bits of another mask. All the bits in the pixel do not have to be used. Windows 95: When the biCompression member is BI_BITFIELDS, Windows 95 supports only the following 16bpp color masks: A 5-5-5 16-bit image, where the blue mask is 0x001F, the green mask is 0x03E0, and the red mask is 0x7C00; and a 5-6-5 16-bit image, where the blue mask is 0x001F, the green mask is 0x07E0, and the red mask is 0xF800.
24 The bitmap has a maximum of 2 (24) colors, and the bmiColors member is NULL. Each 3-byte triplet in the bitmap array represents the relative intensities of blue, green, and red, respectively, for a pixel.
32 The bitmap has a maximum of 2 (32) colors. If the biCompression member of the BITMAPINFOHEADER is BI_RGB, the bmiColors member is NULL. Each DWORD in the bitmap array represents the relative intensities of blue, green, and red, respectively, for a pixel. The high byte in each DWORD is not used.If the biCompression member of the BITMAPINFOHEADER is BI_BITFIELDS, the bmiColors member contains three DWORD color masks that specify the red, green, and blue components, respectively, of each pixel. Each DWORD in the bitmap array represents a single pixel.Windows NT: When the biCompression member is BI_BITFIELDS, bits set in each DWORD mask must be contiguous and should not overlap the bits of another mask. All the bits in the pixel do not have to be used. Windows 95: When the biCompression member is BI_BITFIELDS, Windows 95 supports only the following 32bpp color mask: The blue mask is 0x000000FF, the green mask is 0x0000FF00, and the red mask is 0x00FF0000.
The biClrUsed member of the BITMAPINFOHEADER structure specifies the number of color indices in the color table that are actually used by the bitmap. If the biClrUsed member is set to zero, the bitmap uses the maximum number of colors corresponding to the value of the biBitCount member.
The colors in the bmiColors table should appear in order of importance.
Alternatively, for functions that use DIBs, the bmiColors member can be an array of 16-bit unsigned integers that specify indices into the currently realized logical palette, instead of explicit RGB values. In this case, an application using the bitmap must call the DIB functions (CreateDIBitmap, CreateDIBPatternBrush, and CreateDIBSection) with the iUsage parameter set to DIB_PAL_COLORS.

If the bitmap is a packed bitmap (a bitmap in which the bitmap array immediately follows the BITMAPINFO header and which is referenced by a single pointer), the biClrUsed member must be set to an even number when using the DIB_PAL_COLORS mode so the DIB bitmap array starts on a doubleword boundary.

Note The bmiColors member should not contain palette indices if the bitmap is to be stored in a file or transferred to another application. Unless the application has exclusive use and control of the bitmap, the bitmap color table should contain explicit RGB values.