如果我们有两张图像,并且这两张图像的直方图一样,或者有极高的相似度,那么在一定程度上,我们可以认为这两幅图是一样的,这就是直方图比较的应用之一。要比较两个直方图( and
), 首先必须要选择一个衡量直方图相似度的 对比标准 (
) 。
OpenCV 函数compareHist执行了具体的直方图对比的任务。该函数提供了4种对比标准来计算相似度:
-
Correlation ( CV_COMP_CORREL )
其中
是直方图中bin的数目。
-
Chi-Square ( CV_COMP_CHISQR )
-
Intersection ( CV_COMP_INTERSECT )
-
Bhattacharyya 距离( CV_COMP_BHATTACHARYYA )
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
using namespace std;
using namespace cv;
/** @函数 main */
int main( int argc, char** argv )
{
Mat src_base, hsv_base;
Mat src_test1, hsv_test1;
Mat src_test2, hsv_test2;
Mat hsv_half_down;
/// 装载三张背景环境不同的图像
if( argc < 4 )
{ printf("** Error. Usage: ./compareHist_Demo <image_settings0> <image_setting1> <image_settings2>\n");
return -1;
}
src_base = imread( argv[1], 1 );
src_test1 = imread( argv[2], 1 );
src_test2 = imread( argv[3], 1 );
/// 转换到 HSV
cvtColor( src_base, hsv_base, CV_BGR2HSV );
cvtColor( src_test1, hsv_test1, CV_BGR2HSV );
cvtColor( src_test2, hsv_test2, CV_BGR2HSV );
hsv_half_down = hsv_base( Range( hsv_base.rows/2, hsv_base.rows - 1 ), Range( 0, hsv_base.cols - 1 ) );
/// 对hue通道使用30个bin,对saturatoin通道使用32个bin
int h_bins = 50; int s_bins = 60;
int histSize[] = { h_bins, s_bins };
// hue的取值范围从0到256, saturation取值范围从0到180
float h_ranges[] = { 0, 256 };
float s_ranges[] = { 0, 180 };
const float* ranges[] = { h_ranges, s_ranges };
// 使用第0和第1通道
int channels[] = { 0, 1 };
/// 直方图
MatND hist_base;
MatND hist_half_down;
MatND hist_test1;
MatND hist_test2;
/// 计算HSV图像的直方图
calcHist( &hsv_base, 1, channels, Mat(), hist_base, 2, histSize, ranges, true, false );
normalize( hist_base, hist_base, 0, 1, NORM_MINMAX, -1, Mat() );
calcHist( &hsv_half_down, 1, channels, Mat(), hist_half_down, 2, histSize, ranges, true, false );
normalize( hist_half_down, hist_half_down, 0, 1, NORM_MINMAX, -1, Mat() );
calcHist( &hsv_test1, 1, channels, Mat(), hist_test1, 2, histSize, ranges, true, false );
normalize( hist_test1, hist_test1, 0, 1, NORM_MINMAX, -1, Mat() );
calcHist( &hsv_test2, 1, channels, Mat(), hist_test2, 2, histSize, ranges, true, false );
normalize( hist_test2, hist_test2, 0, 1, NORM_MINMAX, -1, Mat() );
///应用不同的直方图对比方法
for( int i = 0; i < 4; i++ )
{ int compare_method = i;
double base_base = compareHist( hist_base, hist_base, compare_method );
double base_half = compareHist( hist_base, hist_half_down, compare_method );
double base_test1 = compareHist( hist_base, hist_test1, compare_method );
double base_test2 = compareHist( hist_base, hist_test2, compare_method );
printf( " Method [%d] Perfect, Base-Half, Base-Test(1), Base-Test(2) : %f, %f, %f, %f \n", i, base_base, base_half , base_test1, base_test2 );
}
printf( "Done \n" );
return 0;
}