Mask ROI

A mask region of interest (mask ROI) is specified by another (bitonal) image pointed to by the maskROI pointer of the IplImage structure. Mask ROIs allow an application to determine on a pixel-by-pixel basis whether to perform an operation. Pixels corresponding to zeros in the mask are not read (if in a source image) or written (if in the destination image). Pixels corresponding to 1’s in the mask are processed normally. The origin of the mask ROI is aligned to the origin of the rectangular ROI if there is one, or to the origin of the image.

The following example creates a mask image and applies the blur operation to the corresponding mask ROI.

To run the example from the command line, type:
>roi -t2 -m -o<roioffset> -s<roisize>

The source:

void testMaskROI( IplImage* srcAimg, IplImage* srcBimg, IplImage* dstimg,
bool useMaskRoi, int maskRoiOffset, int maskRoiSize )
{
   IplImage *mask = NULL, *img = NULL;
   __try {
      /// create header of a mask image
      mask = iplCreateImageHeader(
         1,                   // one channel for mask
         0,                   // no alpha channel
         IPL_DEPTH_1U,        // one bit data
         "GRAY", "GRAY",      // it is black and white image here
         IPL_DATA_ORDER_PIXEL,
         srcAimg->origin,     // the same origin
         srcAimg->align,      // the same align
         srcAimg->width, srcAimg->height, // the same size of image
         NULL, NULL,          // no roi, no mask
         NULL, NULL           // id, not tiled
      );
      if( !mask ) return;
      /// create a mask image itself
      iplAllocateImage( mask, 0, 0 );
      if( !mask->imageData ) return;
      /// construct mask using XOR srcA and srcB
      iplXor( srcAimg, srcBimg, dstimg );
      /// create mask data by using threshold operation.
      /// Source image for the operation has 3 channels 
      /// so select one of them
      ipSetROItoWholeImage( dstimg );
      dstimg->roi->coi = 1;
      iplThreshold( dstimg, mask, 0x30 );
      /// invert mask
      iplNot( mask, mask );
      /// show mask img
      ipView( mask, " mask image", !is_modal );
      /// create image to operate with mask
      img = iplCreateImageJaehne( IPL_DEPTH_8U, mask->width, mask->height );
      if( !img ) return;
      /// set mask for the image
      img->maskROI = mask;
      /// show source img before blur operation
      ipView( img, " Jaehne's image", !is_modal );
      /// set ROI for the mask image if it is required
      if( useMaskRoi )
         ipSetImageROI( mask, 0, maskRoiOffset,maskRoiOffset, maskRoiSize,maskRoiSize );
      /// blur the image with mask and maybe with mask ROI
      iplBlur( img, img, 5,5, 2,2 );
      /// show result
      ipView( img, "after Blur with mask", is_modal );
   }
   __finally {
      iplDeallocate( mask, IPL_IMAGE_ALL );
      iplDeallocate( img, IPL_IMAGE_ALL );
   }
}