samples/cpp/demhist.cpp#

An example for creating histograms of an image

 1#include "opencv2/core/utility.hpp"
 2#include "opencv2/imgproc.hpp"
 3#include "opencv2/imgcodecs.hpp"
 4#include "opencv2/highgui.hpp"
 5
 6#include <iostream>
 7
 8using namespace cv;
 9using namespace std;
10
11int _brightness = 100;
12int _contrast = 100;
13
14Mat image;
15
16/* brightness/contrast callback function */
17static void updateBrightnessContrast( int /*arg*/, void* )
18{
19    int histSize = 64;
20    int brightness = _brightness - 100;
21    int contrast = _contrast - 100;
22
23    /*
24     * The algorithm is by Werner D. Streidt
25     * (http://visca.com/ffactory/archives/5-99/msg00021.html)
26     */
27    double a, b;
28    if( contrast > 0 )
29    {
30        double delta = 127.*contrast/100;
31        a = 255./(255. - delta*2);
32        b = a*(brightness - delta);
33    }
34    else
35    {
36        double delta = -128.*contrast/100;
37        a = (256.-delta*2)/255.;
38        b = a*brightness + delta;
39    }
40
41    Mat dst, hist;
42    image.convertTo(dst, CV_8U, a, b);
43    imshow("image", dst);
44
45    calcHist(&dst, 1, 0, Mat(), hist, 1, &histSize, 0);
46    Mat histImage = Mat::ones(200, 320, CV_8U)*255;
47
48    normalize(hist, hist, 0, histImage.rows, NORM_MINMAX, CV_32F);
49
50    histImage = Scalar::all(255);
51    int binW = cvRound((double)histImage.cols/histSize);
52
53    for( int i = 0; i < histSize; i++ )
54        rectangle( histImage, Point(i*binW, histImage.rows),
55                   Point((i+1)*binW, histImage.rows - cvRound(hist.at<float>(i))),
56                   Scalar::all(0), -1, 8, 0 );
57    imshow("histogram", histImage);
58}
59
60const char* keys =
61{
62    "{help h||}{@image|baboon.jpg|input image file}"
63};
64
65int main( int argc, const char** argv )
66{
67    CommandLineParser parser(argc, argv, keys);
68    parser.about("\nThis program demonstrates the use of calcHist() -- histogram creation.\n");
69    if (parser.has("help"))
70    {
71        parser.printMessage();
72        return 0;
73    }
74    string inputImage = parser.get<string>(0);
75
76    // Load the source image. HighGUI use.
77    image = imread(samples::findFile(inputImage), IMREAD_GRAYSCALE);
78    if(image.empty())
79    {
80        std::cerr << "Cannot read image file: " << inputImage << std::endl;
81        return -1;
82    }
83
84    namedWindow("image", 0);
85    namedWindow("histogram", 0);
86
87    createTrackbar("brightness", "image", &_brightness, 200, updateBrightnessContrast);
88    createTrackbar("contrast", "image", &_contrast, 200, updateBrightnessContrast);
89
90    updateBrightnessContrast(0, 0);
91    waitKey();
92
93    return 0;
94}