Graphical representation of frequency density of image pixel values. Its helpful in identifying the pixel distribution in an image.
Program:
/*
* File: main.cpp
* Author: Karthick
* Created on April 2, 2010, 11:52 AM
*/
#include < cv.h >
#include < highgui.h >
using namespace std;
IplImage* image = 0;
IplImage* imgHistogram = 0;
IplImage* gray = 0;
CvHistogram* hist;
int main(int argc, char** argv) {
if (argc != 2 || !(image = cvLoadImage(argv[1])))
return -1;
//size of the histogram -1D histogram
int bins = 256;
int hsize[] = {bins};
//max and min value of the histogram
float max_value = 0, min_value = 0;
//value and normalized value
float value;
int normalized;
//ranges - grayscale 0 to 256
float xranges[] = {0, 256};
float* ranges[] = {xranges};
//create an 8 bit single channel image to hold a
//grayscale version of the original picture
gray = cvCreateImage(cvGetSize(image), 8, 1);
cvCvtColor(image, gray, CV_BGR2GRAY);
//Create 3 windows to show the results
cvNamedWindow("original", 1);
cvNamedWindow("gray", 1);
cvNamedWindow("histogram", 1);
//planes to obtain the histogram, in this case just one
IplImage * planes[] = {gray};
//get the histogram and some info about it
hist = cvCreateHist(1, hsize, CV_HIST_ARRAY, ranges, 1);
cvCalcHist(planes, hist, 0, NULL);
cvGetMinMaxHistValue(hist, &min_value, &max_value);
printf("min: %f, max: %f\n", min_value, max_value);
//create an 8 bits single channel image to hold the histogram
//paint it white
imgHistogram = cvCreateImage(cvSize(bins, 200), 8, 1);
cvRectangle(imgHistogram, cvPoint(0, 0), cvPoint(256, 200), CV_RGB(255, 255, 255), -1);
//draw the histogram
for (int i = 0; i < bins; i++) {
value = cvQueryHistValue_1D(hist, i);
normalized = cvRound(value * 200 / max_value);
cvLine(imgHistogram, cvPoint(i, 200), cvPoint(i, 200 - normalized), CV_RGB(0, 0, 0));
printf("%d\n", normalized);
}
//show the image results
cvShowImage("original", image);
cvShowImage("gray", gray);
cvShowImage("histogram", imgHistogram);
cvWaitKey();
return (EXIT_SUCCESS);
}
Output:
