LBitmap::Correlation

Summary

This function compares pCorBitmap (or part of pCorBitmap) with all the areas of the same dimensions in pBitmap and finds those portions that match according to the measure of correlation.

Syntax

#include "ltwrappr.h"

virtual L_INT LBitmap::Correlation (pCorBitmap, pPoints, uMaxPoints, puNumOfPoints, uXStep, uYStep, uThreshold, uFlags = 0)

virtual L_INT LBitmap::Correlation (plCorBitmap, pPoints, uMaxPoints, puNumOfPoints, uXStep, uYStep, uThreshold, uFlags = 0)

Parameters

pBITMAPHANDLE pCorBitmap

Pointer to the bitmap handle that references the bitmap for which to search.

LBitmapBase * plCorBitmap

Pointer to the bitmap object that references the bitmap for which to search.

POINT * pPoints

Pointer to an array of points. This array will be filled with the starting points for the correlated areas.

L_UINT uMaxPoints

Size of the point array. This is also equal to the maximum number of regions in pBitmap that can be found to be correlated.

L_UINT * puNumOfPoints

Pointer to a variable to be updated with the number of areas in pBitmap actually found to be correlated to pCorBitmap. Its maximum value is uMaxPoints.

L_UINT uXStep

Step size in the X direction (along image width), in pixels. For best results, use 1.

L_UINT uYStep

Step size in the Y direction (along image height) ), in pixels. For best results, use 1.

L_UINT uThreshold

Value that indicates the correlation threshold, which is a measure of association required to consider two areas to be correlated. If the correlation value between pCorBitmap and an area in pBitmap is less than the correlation threshold they are uncorrelated. Valid values range from 0 (zero resemblance) to 100 (perfect resemblance).

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 compares pCorBitmap (or a part of pCorBitmap) with all the areas of the same dimensions in Bitmap object and finds those areas that match according to the measure of correlation. Correlation is a measure of association (resemblance) between two images. It varies from 0 (zero resemblance) to 100 (perfect resemblance). This function updates the pPoints parameter with the point of origin for those areas of Bitmap object where the resemblance with pCorBitmap (or part of pCorBitmap) is greater than the value of uThreshold. The pCorBitmap dimensions must be less than or equal to the Bitmap object dimensions.

For example:

Select a bitmap of the object for which you want to look. Put it in pCorBitmap

For example:

$image\Correlation1.gif$

Select a bitmap that contains the object for which you are searching and put it in Bitmap object.

For example:

$image\Correlation2.gif$

Call LBitmap::Correlation from your bitmap object.

The function will update the pPoints array parameter with the point of origin (top-left) for each area of the bitmap pBitmap where the correlation with pCorBitmap is greater than the correlation threshold. The height and width of the rectangles are the same as for pCorBitmap.

The result is:

$image\Correlation3.gif$

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.

The sign flag in the BITMAPHANDLE structure must be the same for all images listed. That is, all images must be either signed or unsigned.

Required DLLs and Libraries

LTIMGEFX
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__CorrelationExample(LAnimationWindow * LAniWnd)  
 
{ 
   L_INT nRet; 
   LBitmap CorBitmap;  
   POINT pPoints[100] = {0}; 
   L_UINT uNumOfPoints;  
   /* Load the bitmap, keeping the bits per pixel of the file */ 
   nRet =CorBitmap.Load(MAKE_IMAGE_PATH(TEXT("ULAY1.BMP"))); 
   if(nRet !=SUCCESS) 
      return nRet; 
    
   /*Apply the correlation filter*/ 
   nRet =LAniWnd->Correlation(&CorBitmap, pPoints, 90 , &uNumOfPoints, 1, 2, 10); 
   if(nRet !=SUCCESS) 
      return nRet; 
   CorBitmap.Free(); 
    
   return SUCCESS; 
}