Victor Image Processing Library How-to Tips

Crop an Image

To crop an image set an area of interest (the area to be kept) and copy it into a new image or extract it into an image file with one of the savefile functions.


Original	Cropped to center 63% of original

In the first example function below, the variable pct represents the relative size of the new cropped image as a percent of the original, in this case, 63%. The dimensions of the new image are calculated and used to allocate a new image of the correct size. The starting x and y positions (stx and sty) in the original image are set and the copyimage function takes the central area and copies it into the new image. The original image is replaced by the smaller cropped version.

VB Source Code | C/C++ Source Code

In the second example function, the area of interest is saved to an image file without altering the original image or creating a new one.

Crop - the VB Source Code

Requires Victor Image Processing Library for Windows v 4.1x or higher.

Declare Function allocimage Lib "VIC32.DLL" (image As imgdes, ByVal wid As Long, ByVal leng As Long, ByVal bppixel As Long) As Long
Declare Function copyimage Lib "VIC32.DLL" (srcimg As imgdes, desimg As imgdes) As Long
Declare Sub copyimgdes Lib "VIC32.DLL" (srcimg As imgdes, desimg As imgdes)
Declare Sub freeimage Lib "VIC32.DLL" (image As imgdes)
Declare Sub RtlMoveMemory Lib "kernel32" (ByVal des As Long, ByVal src As Long, ByVal cnt As Long)
Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (des As Any, ByVal src As Long, ByVal cnt As Long)

' Get BITMAPINFOHEADER from an image descriptor
Private Sub getbmhdata(newBmh As BITMAPINFOHEADER, image As imgdes)
    CopyMemory newBmh, image.bmh, 40   ' 40=size of BITMAPINFOHEADER
End Sub

Public Function crop(image1 As imgdes) As Long
Dim timage As imgdes
Dim bmh As BITMAPINFOHEADER
Dim dx1, dy1, dx2, dy2, rcode, pct As Long

   pct = 63  ' Crop to 63% percent of original size
   getbmhdata bmh, image1

   ' Allocate space for the new image
   dx1 = image1.endx - image1.stx + 1
   dy1 = image1.endy - image1.sty + 1
   dx2 = Int(dx1 * pct / 100)
   dy2 = Int(dy1 * pct / 100)
   rcode = allocimage(timage, dx2, dy2, bmh.biBitCount)
   If (rcode = NO_ERROR) Then
      image1.stx = (dx1 - dx2) / 2
      image1.sty = (dy1 - dy2) / 2
      image1.endx = image1.stx + dx2 - 1
      image1.endy = image1.sty + dy2 - 1

      ' Copy image area into timage
      rcode = copyimage(image1, timage)
      If (rcode = NO_ERROR) Then
         ' Success, free source image
         freeimage image1
         ' Assign timage to image1
         copyimgdes timage, image1
             
      Else ' Error in copying image, release timage memory
         freeimage timage
      End If
   End If
   crop = rcode

End Function

If you merely want to save a small portion of an image then you don't need an entire function, just set the image area to the region of interest and call the desired savefile function. For example to save the image excluding a 10-pixel border around the edge:

	image1.stx = image1.stx + 10
	image1.endx = image1.endx - 10
	image1.sty = image1.sty + 10
	image1.endy = image1.endy - 10
	savetif(filename, image1, 0)

Crop - the C/C++ Source Code

Requires Victor Image Processing Library for Windows v 4.1x or higher.

int crop(imgdes *image1)
{
   imgdes timage;
   int dx1, dy1, dx2, dy2, rcode, pct = 63; // 63% percent of original size

   // Allocate space for the new DIB
   dx1 = image1->endx - image1->stx + 1;
   dy1 = image1->endy - image1->sty + 1;
   dx2 = (int)((long)(dx1) * pct / 100);
   dy2 = (int)((long)(dy1) * pct / 100);
   if((rcode = allocimage(&timage, dx2, dy2, image1->bmh->biBitCount)) == NO_ERROR) {
      image1->stx = (dx1-dx2)/2;
      image1->sty = (dy1-dy2)/2;
      image1->endx = image1->stx + dx2 - 1;
      image1->endy = image1->sty + dy2 - 1;
      // Copy image area into timage
      if((rcode = copyimage(image1, &timage)) == NO_ERROR) {
         // Success, free source image
         freeimage(image1);
         // Assign timage to image1
         copyimgdes(&timage, image1);
         }
      else // Error in resizing image, release timage memory
         freeimage(&timage);
      }
   return(rcode);
}

int crop_and_save(imgdes *image1)
{
   imgdes timage;
   int dx1, dy1, dx2, dy2, rcode, pct = 63; // 63% percent of original size
   int stx, sty, endy, endy;

   // Calculate size of area to save
   dx1 = image1->endx - image1->stx + 1;
   dy1 = image1->endy - image1->sty + 1;
   dx2 = (int)((long)(dx1) * pct / 100);
   dy2 = (int)((long)(dy1) * pct / 100);
   // Save coordinates of original area of interest
   stx = image1->stx;
   sty = image1->sty;
   endx = image1->endx;
   endy = image1->endy;
   // Set area of interest to center 63% of image
   image1->stx = (dx1-dx2)/2;
   image1->sty = (dy1-dy2)/2;
   image1->endx = image1->stx + dx2 - 1;
   image1->endy = image1->sty + dy2 - 1;
   // Save area of interest in TIFF image file
   rcode = savetif("test.tif", image1, 0);
   // Restore area of interest
   image1->stx = stx;
   image1->sty = sty;
   image1->endx = endx;
   image1->endy = endy;
   return(rcode);
}

Victor Image Processing Library homepage | Victor Sample Code