1. histogram.txt
code by Iry - document created on 13 Nov - what-o.com@hotmail.com
void CMy04Dlg::CalcHistogram(IplImage* img, int c)
{
IplImage* channel = cvCreateImage( cvGetSize(img), 8, 1 );
IplImage *hist_img = cvCreateImage(cvSize(100,100), 8, 3);
cvSet( hist_img, cvScalarAll(255), 0 );
CvHistogram *hist_red;
CvHistogram *hist_green;
CvHistogram *hist_blue;
int hist_size = 256;
float range[]={0,256};
float* ranges[] = { range };
float max_value = 0.0;
float max = 0.0;
float w_scale = 0.0;
/* Create a 1-D Arrays to hold the histograms */
hist_red = cvCreateHist(1, &hist_size, CV_HIST_ARRAY, ranges, 1);
hist_green = cvCreateHist(1, &hist_size, CV_HIST_ARRAY, ranges, 1);
hist_blue = cvCreateHist(1, &hist_size, CV_HIST_ARRAY, ranges, 1);
/* Set image to obtain RED as Channel of Interest (COI) */
cvSetImageCOI(img,3);
cvCopy(img,channel);
cvResetImageROI(img);
/* Calculate histogram of the Image and store it in the array */
cvCalcHist( &channel, hist_red, 0, NULL );
/* Calculate and Plot the histograms Green and Blue channels as well */
/* Green channel */
cvSetImageCOI(img,2);
cvCopy(img,channel);
cvResetImageROI(img);
cvCalcHist( &channel, hist_green, 0, NULL );
/* Blue channel */
cvSetImageCOI(img,1);
cvCopy(img,channel);
cvResetImageROI(img);
cvCalcHist( &channel, hist_blue, 0, NULL );
/* Find the minimum and maximum values of the histograms */
cvGetMinMaxHistValue( hist_red, 0, &max_value, 0, 0 );
cvGetMinMaxHistValue( hist_green, 0, &max, 0, 0 );
max_value = (max > max_value) ? max : max_value;
cvGetMinMaxHistValue( hist_blue, 0, &max, 0, 0 );
max_value = (max > max_value) ? max : max_value;
// The variable max_value has the maximum of the three histograms
/* Using the maximum value, Scale/Squeeze the histogram (to fit the image)
*/
cvScale( hist_red->bins, hist_red->bins,
Page 1

2. histogram.txt
((float)hist_img->height)/max_value, 0 );
cvScale( hist_green->bins, hist_green->bins,
((float)hist_img->height)/max_value, 0 );
cvScale( hist_blue->bins, hist_blue->bins,
((float)hist_img->height)/max_value, 0 );
/* Scale/Squeeze the histogram range to image width */
w_scale = ((float)hist_img->width)/hist_size;
/* Plot the Histograms */
for( int i = 0; i < hist_size; i++ )
{
cvRectangle( hist_img, cvPoint((int)i*w_scale ,
hist_img->height),cvPoint((int)(i+1)*w_scale, hist_img->height -
cvRound(cvGetReal1D(hist_red->bins,i))),CV_RGB(255,0,0), -1, 8, 0 );
cvRectangle( hist_img, cvPoint((int)i*w_scale ,
hist_img->height),cvPoint((int)(i+1)*w_scale, hist_img->height -
cvRound(cvGetReal1D(hist_green->bins,i))),CV_RGB(0,255,0), -1, 8, 0 );
cvRectangle( hist_img, cvPoint((int)i*w_scale ,
hist_img->height),cvPoint((int)(i+1)*w_scale, hist_img->height -
cvRound(cvGetReal1D(hist_blue->bins,i))),CV_RGB(0,0,255), -1, 8, 0 );
}
ShowImage( hist_img, IDC_IHist );
cvSaveImage("myoutput_10nov.jpg",hist_img);
}
Page 2