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LBitmap::LocalHistoEqualize

Summary

Linearizes the number of pixels locally in a bitmap, based on the specified color space. This can be used to bring out the detail in dark areas of an image, and smooth the edges between blocks.

Syntax

#include "ltwrappr.h"

virtual L_INT LBitmap::LocalHistoEqualize (nWidthLen, nHeightLen, nxExt, nyExt, uType, uSmooth, uFlags = 0)

Parameters

L_INT nWidthLen

The width of the local histogram equalizer rectangle in pixels. The width should be more than zero.

L_INT nHeightLen

The height of the local histogram equalizer rectangle in pixels. The height should be more than zero.

L_INT nxExt

The extension of the width of the local histogram equalizer rectangle, in pixels.

L_INT nyExt

The extension of the height of the local histogram equalizer rectangle, in pixels.

L_UINT uType

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

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

L_UINT uSmooth

Size of the area to be used when smoothing the edges between localized blocks. Possible values range from 0 to 7, but if nHeightLen is less than or equal to 7 then the maximum value for this item is nHeightLen - 1. If uSmooth = 0 the function will operate without smoothing edges.

L_UINT32 uFlags

Reserved for future use. Must be 0.

Returns

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

Comments

This function applies the histogram equalizer locally on the image. The image is divided into local rectangles of dimension (nWidthLen, nHeightLen). The pixels inside each local rectangle are linearized according the histogram calculated for an extended rectangle around each local rectangle. The extended rectangles are of dimension

((nWidthLen+2 * nxExt) , ( nHeightLen + 2 * nyExt)).

For an example, see the following drawing:

A rectangle and its associated extension, where the histogram is calculated.

Use this function to bring out details in an image that has portions that are too dark or too bright. An example of this is a picture taken with a flashlight in a dark room. In such a picture, the subject receives good light while the background is very dark. The application of the local histogram brings out details, but creates a blocky artifact. Use uSmooth to reduce the blockiness of the result.

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 only in the Document/Medical 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.

Local Equalize Function - Before

Local Equalize Function - After

View additional platform support for this Local 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.

Example

L_INT LBitmap__LocalHistoEqualizeExample(LAnimationWindow * pAniWnd)  
{ 
    
   return pAniWnd->LocalHistoEqualize(15,15,100,100, YUV_SPACE,2 );  
 
}

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