Use OpenCV to separate RGB image into red green and blue components

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This small OpenCV program demonstrates how to separate RGB image into R, G and B components. The program is written in low level programming as there are build in function in OpenCV which would make this code more efficient. However, this example deepens an understanding on how image is split into matrix of pixels and how can each pixel can be manipulated separately.

WRITE CODE

#include <iostream>
#include "cv.h"
#include "highgui.h"

using namespace std;

int main( int argc, char** argv )

{
//load color img specified by first argument
//IplImage *img = cvLoadImage( argv[1]);
IplImage *img = cvLoadImage
(argv[1], CV_LOAD_IMAGE_COLOR );


IplImage *red = cvCreateImage

(cvSize(img->width, img->height ),
img->depth, img->nChannels );

IplImage *green = cvCreateImage
(cvSize(img->width, img->height ),
img->depth, img->nChannels );

IplImage *blue = cvCreateImage
(cvSize(img->width, img->height ),
img->depth, img->nChannels );



// setup the pointer to access img data 
uchar *pImg   = ( uchar* )img->imageData;

// setup pointer to write data 
uchar *pRed   = ( uchar* )red->imageData;
uchar *pGreen = ( uchar* )green->imageData;
uchar *pBlue  = ( uchar* )blue->imageData;    



int i, j, rED, gREEN, bLUE, byte;
for( i = 0 ; i < img->height ; i++ ) 
{

  for( j = 0 ; j < img->width ; j++ ) 
  {
  rED = pImg[i*img->widthStep + j*img->nChannels + 2];

  gREEN = pImg[i*img->widthStep + j*img->nChannels + 1];
  bLUE = pImg[i*img->widthStep + j*img->nChannels + 0];
  // RED

  pRed[i*img->widthStep + j*img->nChannels + 2] = rED;
  // GREEN
  pGreen[i*img->widthStep + j*img->nChannels + 1] = gREEN;

  // BLUE
  pBlue[i*img->widthStep + j*img->nChannels + 0] = bLUE;
  }
}
// save images

cvSaveImage( argv[2], red );
cvSaveImage( argv[3], green );
cvSaveImage( argv[4], blue );

return 0;

}

COMPILE

g++ `pkg-config opencv --cflags --libs` \ 
separate-RGB.cpp -o separate-RGB

USAGE

./separate-RGB img.png red.png green.png blue.png

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