#include "l_bitmap.h"

L_LTIMGCLR_API L_INT L_GammaCorrectBitmapExt(pBitmap, uGamma, uFlags)


pointer to the bitmap handle

L_UINT uGamma;

gamma value

L_UINT uFlags;


Adjusts the intensity of colors in a bitmap by changing the gamma constant that is used to map the intensity values. Either of two different color spaces can be specified.

Parameter Description
pBitmap Pointer to the bitmap handle referencing the target bitmap.
uGamma Any value greater than 0 that represents the gamma value. This value is divided internally by 100.
uFlags Flag that indicates which color space to use. Possible values are:
  Value Meaning
  RGB_SPACE [0x0001] Adjust the intensity of the pixel colors across the RGB color space.
  YUV_SPACE [0x0002] Adjust the intensity of the pixel colors across the YUV color space.



The function was successful.

< 1

An error occurred. Refer to Return Codes.


This function is like the L_GammaCorrectBitmap function, but has been extended to allow the specification of the colorspace to be used.

Intensity values ideally follow a logarithmic progression, because the eye perceives changes in intensity as being equal when the ratio of change is equal. For example, we would see a change from 0.1 to 0.2 as being equal to a change from 0.2 to 0.4.

Gamma is a standard constant that is used to calculate the progression. For most CRTs the gamma constant is in the range of 2.2 to 2.5.

To update a status bar or detect a user interrupt during execution of this function, refer to L_SetStatusCallback.

This function supports 12 and 16-bit grayscale and 48 and 64-bit color images. Support for 12 and 16-bit grayscale and 48 and 64-bit color images is available in the Document and Medical Imaging toolkits.

This function does not support 32-bit grayscale images. It returns the error code ERROR_GRAY32_UNSUPPORTED if a 32-bit grayscale image is passed to this function.

This function adjusts the gamma constant used to map color intensity values in the image data. If the image has a LUT, the function will work on the LUT, not the image data. If the image has a LUT and you want to work on the image data, set the  UseLUT Flag in the BITMAPHANDLE structure to FALSE. Then, after calling the function, reset the UseLUT flag to TRUE as follows:

pBitmap->Flags.UseLUT = FALSE;

 L_GammaCorrectBitmap(pBitmap, 90);

pBitmap->Flags.UseLUT = TRUE;

Required DLLs and Libraries


For a listing of the exact DLLs and Libraries needed, based on the toolkit version, refer to Files To Be Included With Your Application.


Win32, x64, Linux.

See Also


L_GammaCorrectBitmap, L_ChangeBitmapIntensity, L_ChangeBitmapContrast, L_HistoContrastBitmap, L_StretchBitmapIntensity, L_RemapBitmapIntensity, L_InvertBitmap, L_ChangeBitmapHue, L_ChangeBitmapSaturation, L_HistoEqualizeBitmap, L_FillBitmap, L_GetPixelColor, L_PutPixelColor, L_GetBitmapHistogram, L_DlgGammaAdjustment, L_WindowLevel, L_ChannelMix, L_DeinterlaceBitmap, L_DesaturateBitmap, L_EdgeDetectStatisticalBitmap, L_LightControlBitmap, L_SmoothEdgesBitmap, L_LocalHistoEqualizeBitmap, L_AddWeightedBitmaps, L_ColorMergeBitmap, L_ColorSeparateBitmap, L_ConvertColorSpace, L_MultiplyBitmap, L_AutoColorLevelBitmap, L_ColorLevelBitmap, L_CorrelationBitmap, L_GrayScaleToDuotone, L_GrayScaleToMultitone, L_HolesRemovalBitmapRgn, L_SelectiveColorBitmap, L_SkeletonBitmap, L_ChangeHueSatIntBitmap, L_ColorReplaceBitmap, L_ColorThresholdBitmap, L_MathFunctionBitmap, L_SegmentBitmap, L_AdaptiveContrastBitmap, L_ApplyMathLogicBitmap, L_ColorIntensityBalance, L_ColorizeGrayBitmap, L_ContBrightIntBitmap, L_DigitalSubtractBitmap, L_DynamicBinaryBitmap, L_EdgeDetectEffectBitmap, L_FunctionalLightBitmap, L_MultiScaleEnhancementBitmap, L_SelectBitmapData, L_ShiftBitmapData


Raster Image Functions: Modifying Intensity Values


Changing Brightness and Contrast


Raster Image Functions: Changing Brightness and Contrast


The following example sets the gamma value of the bitmap to 2.5 in the YUV color space:

#define MAKE_IMAGE_PATH(pFileName) TEXT("C:\\Users\\Public\\Documents\\LEADTOOLS Images\\")pFileName 
L_INT GammaCorrectBitmapExtExample(L_VOID) 
   L_INT nRet; 
   BITMAPHANDLE LeadBitmap; 
   nRet = L_LoadBitmap (MAKE_IMAGE_PATH(TEXT("sample5.cmp")), &LeadBitmap,sizeof(BITMAPHANDLE), 0, ORDER_BGR, NULL, NULL); 
   if(nRet !=SUCCESS) 
      return nRet; 
   nRet = L_GammaCorrectBitmapExt (&LeadBitmap, 250, YUV_SPACE); 
   if(nRet !=SUCCESS) 
      return nRet; 
   nRet = L_SaveBitmap(MAKE_IMAGE_PATH(TEXT("Result.BMP")), &LeadBitmap, FILE_BMP, 24, 0, NULL); 
   if(nRet !=SUCCESS) 
      return nRet; 
   //free bitmap 
   return SUCCESS; 

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