L_GammaCorrectBitmapExt

#include "l_bitmap.h"

L_LTIMGCLR_API L_INT L_GammaCorrectBitmapExt(pBitmap, uGamma, 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.

Parameters

pBITMAPHANDLE pBitmap

Pointer to the bitmap handle referencing the target bitmap.

L_UINT uGamma

Any value greater than 0 that represents the gamma value. This value is divided internally by 100.

L_UINT 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.

Returns

Value Meaning
SUCCESS The function was successful.
< 1 An error occurred. Refer to Return Codes.

Comments

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

Platforms

Win32, x64, Linux.

See Also

Functions

Topics

Example

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

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 
   if(LeadBitmap.Flags.Allocated) 
      L_FreeBitmap(&LeadBitmap); 
   return SUCCESS; 
} 

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