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L_HistoEqualizeBitmap

Summary

Linearizes the number of pixels, in a bitmap, based on the specified color space. This function is also useful for pre-processing images for the purpose of improving barcode recognition results.

Syntax

#include "l_bitmap.h"

L_LTIMGCLR_API L_INT L_HistoEqualizeBitmap(pBitmap, uFlags)

Parameters

pBITMAPHANDLE pBitmap

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

L_UINT32 uFlags

Flag that indicates which color space to equalize. Possible values are:

Value	Meaning
RGB_SPACE	[0x0001] Linearizes the number of pixels across the RGB color space.(separated channels).
YUV_SPACE	[0x0002] Linearizes the number of pixels across the YUV color space.(Best results).
GRAY_SPACE	[0x0004] Linearizes the number of pixels per gray level in a gray level representation of the image.

Returns

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

Comments

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

Previously this function only equalized the number of pixels per gray level, using a gray level representation of the image. This functionality is now obtained by passing GRAY_SPACE for uFlags.

For the best results, set uFlags to YUV_SPACE.

This function can process the whole image or a region of the image.

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.

Histogram Equalize Function - Before

Histogram Equalize Function - After

View additional platform support for this Histogram Equalize function.

Required DLLs and Libraries

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

Platforms

Win32, x64, Linux.

Example

For complete sample code, refer to the CHILD.C module of the DEMO example.
This example loads a bitmap and applies histogram equalization.

L_INT HistoEqualizeBitmapExample(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; 
 
   /* Histogram equalize the bitmap */ 
   nRet = L_HistoEqualizeBitmap(&LeadBitmap, 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; 
}