#include "l_bitmap.h"

L_LTIMGCLR_API L_INT L_AdaptiveContrastBitmap (pBitmap, uDim, uAmount, uFlags)

Performs adaptive contrast enhancement (ACE) to regions that are originally low in contrast.



Pointer to the bitmap handle referencing the bitmap to be changed.


Dimensions of the neighborhood used for filtering (uDim x uDim), in pixels.

L_UINT uAmount

Value that represents an adjustment factor. Its range starts from 100 and has no upper limit.

L_UINT uFlags

Value that indicates the adjustment method. Possible values are:

Value Meaning
ACE_EXP [0x0001] Apply exponential adjustment.
ACE_LIN [0x0002] Apply linear adjustment.


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


Adaptive contrast enhancement (ACE) adjusts bitmap contrast by giving more contrast to areas which are originally low in contrast. This is different from histogram-based techniques which are based on all bitmap pixels (the histogram itself).

Local histogram equalization is another technique that can be used to reveal detail of areas, since it depends on area pixels only. Use L_LocalHistoEqualizeBitmap to perform a local histogram equalization.

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.

Required DLLs and Libraries


Win32, x64, Linux.

See Also




This example loads a bitmap and applies Adaptive Contrast Enhancement

L_INT AdaptiveContrastBitmapExample(L_VOID) 
   L_INT nRet; 
   BITMAPHANDLE LeadBitmap;   /* Bitmap handle to hold the loaded image. */ 
   /* Load the bitmap, keeping the bits per pixel of the file */ 
   nRet = L_LoadBitmap(MAKE_IMAGE_PATH(TEXT("IMAGE1.CMP")), &LeadBitmap, sizeof(BITMAPHANDLE), 0, ORDER_BGR, NULL, NULL);  
   if(nRet !=SUCCESS) 
      return nRet; 
   /* Apply Adaptive Contrast Enhancement */ 
   nRet = L_AdaptiveContrastBitmap(&LeadBitmap, 9, 200, ACE_LIN); 
   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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