/*
  Pixel manipulation is necessary when applying a homography to an image.
  This demo illustrates how this is done.
  The top half of the image is exchanged with the bottom half.
  J.K. Johnstone
 */

#include <cv.h>      // these two OpenCV libraries should be included 
#include <highgui.h> // in any OpenCV program
#include <iostream>
using namespace std;

IplImage *srcImg;     // original image
IplImage *createdImg; // image created by pixel manipulation

int main (int argc, char **argv)
{
  if (argc != 2) 
    { cout << "Need an image parameter (jpg or ppm/pgm)" << endl; exit(-1); }
  srcImg = cvLoadImage (argv[1]);

  createdImg = cvCreateImage (cvSize(srcImg->width, srcImg->height),
			  	  	srcImg->depth, srcImg->nChannels);
  if (srcImg->depth != 8)
    { 
      cout << "Sorry, I assumed 8-bit channels: you'd better generalize " 
	   << "the code before you work with this image." << endl; 
      exit(-1); 
    }
  // for example, 32-bit channels would simply cast the type to float*, not uchar*
  int midrow = srcImg->height / 2;
  int x,y,rgb;
  if (srcImg->nChannels == 1)  // grey-scale image
    for (x=0; x<srcImg->width; x++)
      {
	for (y=0; y<midrow; y++)              // top is bottom
	  ((uchar *)(createdImg->imageData + createdImg->widthStep*y))[x]
	    = ((uchar *)(srcImg->imageData + srcImg->widthStep*(y+midrow)))[x];
	for (y=midrow; y<srcImg->height; y++) // and bottom is top
	  ((uchar *)(createdImg->imageData + createdImg->widthStep*y))[x]
	    = ((uchar *)(srcImg->imageData + srcImg->widthStep*(y-midrow)))[x];
      } 
  else if (srcImg->nChannels == 3) // RGB image
    for (x=0; x<srcImg->width; x++)
      {
	for (y=0; y<midrow; y++)
	  for (rgb=0; rgb<3; rgb++)
	    ((uchar *)(createdImg->imageData + createdImg->widthStep*y))[3*x + rgb]
	      = ((uchar *)(srcImg->imageData + srcImg->widthStep*(y+midrow)))[3*x + rgb];
	for (y=midrow; y<srcImg->height; y++)
	  for (rgb=0; rgb<3; rgb++)
	    ((uchar *)(createdImg->imageData + createdImg->widthStep*y))[3*x + rgb]
	      = ((uchar *)(srcImg->imageData + srcImg->widthStep*(y-midrow)))[3*x + rgb];
      }

  cvNamedWindow ("pixel manipulation", 1);
  cvShowImage   ("pixel manipulation", createdImg);
  cvWaitKey(0);
  cvDestroyWindow("foo");
  cvReleaseImage (&srcImg);
  cvReleaseImage (&createdImg);
  return 0;
}