2.2.2.3 BitmapInfoHeader Object

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


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HeaderSize

Width

Height

Planes

BitCount

Compression

ImageSize

XPelsPerMeter

YPelsPerMeter

ColorUsed

ColorImportant

HeaderSize (4 bytes): A 32-bit unsigned integer that defines the size of this object, in bytes.

Width (4 bytes): A 32-bit signed integer that defines the width of the DIB, in pixels. This value MUST be positive.

This field SHOULD specify the width of the decompressed image file, if the Compression value specifies JPEG or PNG format.<44>

Height (4 bytes): A 32-bit signed integer that defines the height of the DIB, in pixels. This value MUST NOT be zero.

Value

Meaning

0x00000000 < value

If this value is positive, the DIB is a bottom-up bitmap, and its origin is the lower-left corner.

This field SHOULD specify the height of the decompressed image file, if the Compression value specifies JPEG or PNG format.

value < 0x00000000

If this value is negative, the DIB is a top-down bitmap, and its origin is the upper-left corner. Top-down bitmaps do not support compression.

Planes (2 bytes): A 16-bit unsigned integer that defines the number of planes for the target device. This value MUST be 0x0001.

BitCount (2 bytes): A 16-bit unsigned integer that defines the number of bits that define each pixel and the maximum number of colors in the DIB. This value MUST be in the BitCount Enumeration (section 2.1.1.3).

Compression (4 bytes): A 32-bit unsigned integer that defines the compression mode of the DIB. This value MUST be in the Compression Enumeration (section 2.1.1.7).

This value MUST NOT specify a compressed format if the DIB is a top-down bitmap, as indicated by the Height value.

ImageSize (4 bytes): A 32-bit unsigned integer that defines the size, in bytes, of the image.

If the Compression value is BI_RGB, this value SHOULD be zero and MUST be ignored.<45>

If the Compression value is BI_JPEG or BI_PNG, this value MUST specify the size of the JPEG or PNG image buffer, respectively.

XPelsPerMeter (4 bytes): A 32-bit signed integer that defines the horizontal resolution, in pixels-per-meter, of the target device for the DIB.

YPelsPerMeter (4 bytes): A 32-bit signed integer that defines the vertical resolution, in pixels-per-meter, of the target device for the DIB.

ColorUsed (4 bytes): A 32-bit unsigned integer that specifies the number of indexes in the color table used by the DIB, as follows:

  • If this value is zero, the DIB uses the maximum number of colors that correspond to the BitCount value.

  • If this value is nonzero and the BitCount value is less than 16, this value specifies the number of colors used by the DIB.

  • If this value is nonzero and the BitCount value is 16 or greater, this value specifies the size of the color table used to optimize performance of the system palette.

Note If this value is nonzero and greater than the maximum possible size of the color table based on the BitCount value, the maximum color table size SHOULD be assumed.

ColorImportant (4 bytes): A 32-bit unsigned integer that defines the number of color indexes that are required for displaying the DIB. If this value is zero, all color indexes are required.

A DIB is specified by a DeviceIndependentBitmap Object (section 2.2.2.9).

When the array of pixels in the DIB immediately follows the BitmapInfoHeader, the DIB is a packed bitmap. In a packed bitmap, the ColorUsed value MUST be either 0x00000000 or the actual size of the color table.