Victor Image Processing Library How-to Tips

Pattern Recognition, Find a Mark in an Image

This procedure supports grayscale images. Use the Victor Library conversion functions to convert color or black and white images to 8-bit grayscale.

In general, the steps are:

• determine the dimensions and pixel depth of the test and reference images
• allocate buffer space for the images
• load the images
• fill the result image with correlation coefficient data calculated between the test image and the reference image
• sort the correlation coefficient data to determine the most probable location of the mark

Test image	Reference image	Result image, mark found at (84, 213)

The brightest pixel in the result image represents the most probable location of the reference mark. In this case that is at location (84, 213).

Find a Mark - the Visual Basic Source Code

' Add the data type definition and function declarations to vicdef32.bas ...............................................

Type COORD_VAL
   val As Long
   x As Long
   y As Long
End Type

Public Declare Function correlationcoef Lib "vicstats.dll" (ByRef srcimg As imgdes, ByRef oprimg As imgdes, ByRef pCoef As Double) As Long
Public Declare Function correlateimages Lib "vicstats.dll" (ByRef srcimg As imgdes, ByRef oprimg As imgdes, ByRef resimg As imgdes) As Long
Public Declare Function calcavglevelfloat Lib "vicstats.dll" (ByRef srcimg As imgdes, ByRef redavg As Double, ByRef grnavg As Double, ByRef bluavg As Double) As Long
Public Declare Function sortpixelsbyval Lib "vicstats.dll" (ByRef srcimg As imgdes, ByRef first_elem As COORD_VAL, ByVal nelem As Long) As Long

' The Functions .................................................... 
Private Function findmark(srcimg As imgdes, oprimg As imgdes, resimg As imgdes, ptarray As COORD_VAL, numelem As Long) As Long
Dim rcode As Long

'   Fill the result image with correlation coefficient data
    rcode = correlateimages(srcimg, oprimg, resimg)
                                                      
   If (rcode = NO_ERROR) Then
        '  The pixel data in the result image will be sorted
        '  and placed in the array in descending order
       rcode = sortpixelsbyval(resimg, ptarray, numelem)

   End If
    
   findmark = rcode

End Function


Private Sub mnufindmark_Click()
Dim rcode As Long
Dim testimage As imgdes
Dim markimage As imgdes
Dim testfile As JpegData
Dim markfile As JpegData
Dim scols, srows, ocols, orows As Long

Dim ptarray() As COORD_VAL
Dim numelem As Long

   ' For easier understanding of the sample code no error checking is performed here
   ' but recognize that you should always test the return code to verify that each function is successful 
   rcode = jpeginfo("testc.jpg", testfile)
   rcode = allocimage(testimage, testfile.width, testfile.length, testfile.vbitcount)
   rcode = loadjpg("testc.jpg", testimage)

   rcode = jpeginfo("register.jpg", markfile)
   rcode = allocimage(markimage, markfile.width, markfile.length, markfile.vbitcount)
   rcode = loadjpg("register.jpg", markimage)

   scols = testimage.endx - testimage.stx + 1
   srows = testimage.endy - testimage.sty + 1
   ocols = markimage.endx - markimage.stx + 1
   orows = markimage.endy - markimage.sty + 1

   numelem = scols * srows

   ' Allocate an array to hold the pixel data for the sorting
   ReDim ptarray(0 To numelem - 1) As COORD_VAL
   
   rcode = findmark(testimage, markimage, testimage, ptarray(0), numelem)
   If (rcode = NO_ERROR) Then
      MsgBox ("Most probable location for mark: " & ptarray(0).val & "  (" & ptarray(0).x & "," & ptarray(0).y & ")")
   End If

   rcode = savejpg("testr.jpg", testimage, 50)
   freeimage markimage
   freeimage testimage

End Sub

Find a Mark - the C Source Code

// Add these declarations to vicdefs.h
typedef struct { unsigned val, x, y; } COORD_VAL;
int WINAPI correlationcoef(imgdes *srcimg, imgdes *oprimg, double *pCoef);
int WINAPI correlateimages(imgdes *srcimg, imgdes *oprimg, imgdes *resimg);
int WINAPI calcavglevelfloat(imgdes *srcimg, double *redavg, double *grnavg, double *bluavg);
int WINAPI sortpixelsbyval(imgdes *srcimg, COORD_VAL *darray, int nelem);

int findmark(imgdes *srcimg, imgdes *oprimg, imgdes *resimg, COORD_VAL *ptarray, int numelem)  
{
   int rcode;

   // Fills the result image with correlation coefficient data
   rcode = correlateimages(srcimg, oprimg, resimg); 
                                                      
   if(rcode == NO_ERROR) {
      // The pixel data in the result image will be sorted
      // and placed in the array in descending order
      rcode = sortpixelsbyval(resimg, ptarray, numelem);
      }
   return (rcode);
}

void DoMenuFindmark(HWND hWnd)
{
   int rcode;
   imgdes testimage;
   imgdes markimage;
   JpegData testfile;
   JpegData markfile;
   int scols, srows, ocols, orows;

   COORD_VAL *ptarray;
   int numelem;

   // For easier understanding of the sample code no error checking is performed here
   // but recognize that you should always test the return code to verify that each function is successful 
   rcode = jpeginfo("testc.jpg", &testfile);
   rcode = allocimage(&testimage, testfile.width, testfile.length, testfile.vbitcount);
   rcode = loadjpg("testc.jpg", &testimage);

   rcode = jpeginfo("register.jpg", &markfile);
   rcode = allocimage(&markimage, markfile.width, markfile.length, markfile.vbitcount);
   rcode = loadjpg("register.jpg", &markimage);

   scols = CALC_WIDTH(&testimage);
   srows = CALC_HEIGHT(&testimage);
   ocols = CALC_WIDTH(&markimage);
   orows = CALC_HEIGHT(&markimage);

   numelem =  scols * srows;

   // Allocate an array to hold the pixel data for the sorting
   ptarray = calloc(numelem, sizeof(COORD_VAL));
   rcode = findmark(&testimage, &markimage, &testimage, ptarray, numelem);
   if(rcode == NO_ERROR) {
      char szBuff[128];

      // Display the values for the four most likely locations
      wsprintf(szBuff, "Most probable locations for mark:"
         "\n%3d: (%3d, %3d)"
         "\n%3d: (%3d, %3d)"
         "\n%3d: (%3d, %3d)"
         "\n%3d: (%3d, %3d)",
          ptarray[0].val, ptarray[0].x, ptarray[0].y, 
          ptarray[1].val, ptarray[1].x, ptarray[1].y,
          ptarray[2].val, ptarray[2].x, ptarray[2].y,
          ptarray[3].val, ptarray[3].x, ptarray[3].y
          );
      MessageBox(hWnd, szBuff, szAppName, MB_OK);
      }

   if(ptarray)
      free(ptarray);

   savejpg("testr.jpg", &testimage, 50);
   freeimage(&markimage);
   freeimage(&testimage);
}







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