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HT_ComputeRGBGammaTable function (winddi.h)

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The HT_ComputeRGBGammaTable function causes GDI to compute device red, green, and blue intensities based on gamma numbers.

Syntax

LONG HT_ComputeRGBGammaTable(
  [in]  USHORT GammaTableEntries,
  [in]  USHORT GammaTableType,
  [in]  USHORT RedGamma,
  [in]  USHORT GreenGamma,
  [in]  USHORT BlueGamma,
  [out] LPBYTE pGammaTable
);

Parameters

[in] GammaTableEntries

Specifies the total number of steps in the table for each of red, green, and blue intensities. This value must greater than 1 and less than or equal to 256 (that is, 2 <= GammaTableEntries <= 256). For example, a value of 256 means there are 256 red entries, 256 green entries, and 256 blue entries in the gamma table.

[in] GammaTableType

Specifies pGammaTable's organization. Valid table types are:

GammaTableType Meaning
0 The gamma table's red, green, and blue values are interleaved together. Each gamma step is 3 bytes; 1 byte each for red, green, and blue.
1 The red, green, and blue tables are packed separately; that is, the entire red table is followed by the entire green table, which is followed by the entire blue table. Individual entries are 1 byte each, making each subtable a total of GammaTableEntries bytes in length.

[in] RedGamma

Specifies the red gamma value. This USHORT value is interpreted as a real number whose four least-significant digits are to the right of the (implied) decimal point. For example, a gamma value of 10000 represents the real number 1.0000, and 12345 represents 1.2345. The minimum gamma value allowed is 0.0000, and the maximum allowable value is 6.5535.

[in] GreenGamma

Specifies the green gamma value. This USHORT value is interpreted as a real number whose four least-significant digits are to the right of the (implied) decimal point. For example, a gamma value of 10000 represents the real number 1.0000, and 12345 represents 1.2345. The minimum gamma value allowed is 0.0000, and the maximum allowable value is 6.5535.

[in] BlueGamma

Specifies the blue gamma value. This USHORT value is interpreted as a real number whose four least-significant digits are to the right of the (implied) decimal point. For example, a gamma value of 10000 represents the real number 1.0000, and 12345 represents 1.2345. The minimum gamma value allowed is 0.0000, and the maximum allowable value is 6.5535.

[out] pGammaTable

Pointer to the array of bytes in which the gamma table's red, green, and blue intensities will be written. The returned table is organized as specified by the GammaTableType parameter.

Return value

The return value is the number of gamma entries written to pGammaTable; upon success, this value is equal to GammaTableEntries. If GammaTableEntries is less than 2 or greater than 256, the return value is 0.

The red, green, and blue intensities returned in pGammaTable range from 0 to 255.

Remarks

GDI halftone service routines use a special palette to do halftoning. If the device selects an 8-bit per pixel palette from a pool of 24-bit device colors for a 16-bit or 24-bit type surface, GDI assumes red, green, and blue color steps; each has equal brightness.

GDI provides this service so that the driver can query the 8-bit per pixel halftone palette used by GDI or compute gamma corrected and equalized RGB color intensities for the device.

Requirements

Requirement Value
Minimum supported client Available in Windows 2000 and later versions of the Windows operating systems.
Target Platform Universal
Header winddi.h (include Winddi.h)
Library Win32k.lib
DLL Win32k.sys