Using Norm in an ROI

In this example, the program zooms the source image and then averages the image's pixel values. To do this, the program computes the L₁ norm (that is, the sum of absolute values of pixels in the ROI) and divides it by the number of pixels in the ROI. Pixels in the destination image's ROI are set to this average value using the iplSet() function.

This average-and-set operation is performed in a loop, in which the ROI is gradually shifted. After the loop is completed, each pixel value in the destination image is equal to the average of pixel values in the corresponding region of the input image.

To run the example from the command line, type:
> roi -t3 -s<roisize> [-z<zoom factor>] [-i =<L|C>]
(-i specifies the interpolation mode).

The source:

int testRoiNorm( int tsize, int zoom, bool linear )
{
   const rawSize = 300;                /// raw size of image
   const int numof = rawSize / tsize;  /// number of tiles in one dimension
   const int tarea = tsize * tsize, size = tsize * numof;

   IplImage *dst=NULL, *src=NULL;

   __try {

      dst = iplCreateImageJaehne( IPL_DEPTH_8U, size, size );
      src = iplCloneImage( dst );
      if( !src || !dst ) return -1;
      /// make source image by using Zoom function and show it
      iplZoom( dst, src, zoom,1, zoom,1, linear ? IPL_INTER_LINEAR : IPL_INTER_CUBIC );
      sprintf( msg, " Zoom( Jaehne, %d, %s )", zoom, (linear ? "LINEAR":"CUBIC") );
      ipView( src, msg, !is_modal );

      /// the images will use ROI for operations,
      /// the source image uses the ROI to calculate L1 norm,
      /// the destination image uses the ROI to set value
      IplROI roi = { 0, 0,0, tsize,tsize };
      src->roi = dst->roi = &roi;

      /// for each ROI
      for( int y=0; y<numof; ++y ) {
         roi.yOffset = tsize * y;
         for( int x=0; x<numof; ++x ) {
            roi.xOffset = tsize * x;
            /// get mean value from source
            int value = (int)( iplNorm( src, NULL, IPL_L1 ) / tarea );
            /// put this value to destination
            iplSet( dst, value );
         }
      }
      /// show result
      sprintf( msg, " Filled by norm of ROIs %dx%d", tsize, tsize );
      ipView( dst, msg , is_modal );
   }
   __finally {
      /// preserve automatic variable and free memory
      src->roi = dst->roi = NULL;
      iplDeallocate( src, IPL_IMAGE_ALL );
      iplDeallocate( dst, IPL_IMAGE_ALL );
   }
   return 0;
}