영상 정합(image patch similarity)

영상의 패치 정합

1. SSD(Sum of Squared Difference)

같은 위치에 있는 픽셀의 차를 구해서 제곱한 값을 다 더해 영역의 유사성 측정을 한다.

유사할 경우 0에 가깝다.

2. SAD(Sum Of Absolute Difference)

같은 위치에 있는 픽셀의 차를 절대값 하고 다 더해 영역의 유사성 측정을 한다.

SSD와 마찬가지로 유사할 경우 0에 가깝다.

3. NCC(Normalized Cross Correlation)

NCC는 SSD와 SAD가 갖는 밝기 차의 문제를 결하기 위해 사용하는 중 하나이다. 

두 영역의 픽셀 평균값과 표준편차를 계산하여 평균 값기가 0, 표준편차는 1이 되도록 정규화한다.

m은 평균 밝기를 나타내며 σ는 표준편차이다.

#include <cv.h>
#include <highgui.h>
#include <iostream>
 
using namespace cv;
using namespace std;
 
int SSD(Mat &src1, Mat &src2, Point pt1, Point pt2, int patch_size)
{
    // Range Check
    if ((pt1.x - patch_size) < 0 || (pt2.x - patch_size) < 0 || (pt1.x + patch_size) >= src1.rows ||
        (pt2.x + patch_size) >= src2.rows || (pt1.y - patch_size) < 0 || (pt2.y - patch_size) < 0 ||
        (pt1.y + patch_size) >= src1.cols || (pt2.y + patch_size) >= src2.cols)
        throw exception("SSD::Inavlid range");
 
    // Image Channel Check
    if (src1.channels() != src2.channels())
        throw exception("SSD::Image channel not same");
 
    int nSum = 0;
    
    unsigned char *src1_ptr = (unsigned char*)src1.data;
    unsigned char *src2_ptr = (unsigned char*)src2.data;
    int src1_cn = src1.channels();
    int src2_cn = src2.channels();
 
    for (int r = -patch_size; r <= patch_size; r++)
    {
        for (int c = -patch_size; c <= patch_size; c++)
        {
            for (int l = 0; l <= src1_cn; l++)
            {
                nSum += ((src1_ptr[(pt1.x + r) * src1.cols * src1_cn + (pt1.y + c) * src1_cn + l]) - (src2_ptr[(pt2.x + r) * src2.cols * src2_cn + (pt2.y + c) * src2_cn + l]))
                    * ((src1_ptr[(pt1.x + r) * src1.cols * src1_cn + (pt1.y + c) * src1_cn + l]) - (src2_ptr[(pt2.x + r) * src2.cols * src2_cn + (pt2.y + c) * src2_cn + l]));
            }
        }
    }
    
    return nSum;
}
 
int SAD(Mat &src1, Mat &src2, Point pt1, Point pt2, int patch_size)
{
    // Range Check
    if ((pt1.x - patch_size) < 0 || (pt2.x - patch_size) < 0 || (pt1.x + patch_size) >= src1.rows ||
        (pt2.x + patch_size) >= src2.rows || (pt1.y - patch_size) < 0 || (pt2.y - patch_size) < 0 ||
        (pt1.y + patch_size) >= src1.cols || (pt2.y + patch_size) >= src2.cols)
        throw exception("SAD::Inavlid range");
 
    // Image Channel Check
    if (src1.channels() != src2.channels())
        throw exception("SAD::Image channel not same");
    
    int nSum = 0;
 
    unsigned char *src1_ptr = (unsigned char*)src1.data;
    unsigned char *src2_ptr = (unsigned char*)src2.data;
    int src1_cn = src1.channels();
    int src2_cn = src2.channels();
 
    for (int r = -patch_size; r <= patch_size; r++)
    {
        for (int c = -patch_size; c <= patch_size; c++)
        {
            for (int l = 0; l < src1_cn; l++)
            {
                nSum += abs((src1_ptr[(pt1.x + r) * src1.cols * src1_cn + (pt1.y + c) * src1_cn + l]) - (src2_ptr[(pt2.x + r) * src2.cols * src2_cn + (pt2.y + c) * src2_cn + l]));    
            }
        }
    }
 
    return nSum;
}
 
float NCC(Mat &src1, Mat &src2, Point pt1, Point pt2, int patch_size)
{
    // Range Check
    if ((pt1.x - patch_size) < 0 || (pt2.x - patch_size) < 0 || (pt1.x + patch_size) >= src1.rows ||
        (pt2.x + patch_size) >= src2.rows || (pt1.y - patch_size) < 0 || (pt2.y - patch_size) < 0 ||
        (pt1.y + patch_size) >= src1.cols || (pt2.y + patch_size) >= src2.cols)
        throw exception("NCC::Inavlid range");
 
    // Image Channel Check
    if (src1.channels() != src2.channels())
        throw exception("NCC::Image channel not same");
 
    // calcurate average, stendard deviation
    int nSum1 = 0, nSum2 = 0;
    int nSqr1 = 0, nSqr2 = 0;
    
    unsigned char *src1_ptr = (unsigned char*)src1.data;
    unsigned char *src2_ptr = (unsigned char*)src2.data;
    int src1_cn = src1.channels();
    int src2_cn = src2.channels();
        
    for (int r = -patch_size; r <= patch_size; r++)
    {
        for (int c = -patch_size; c <= patch_size; c++)
        {
            for (int l = 0; l < src1_cn; l++)
            {
                int t1 = src1_ptr[(pt1.x + r) * src1.cols * src1_cn + (pt1.y + c) * src1_cn + l];
                int t2 = src2_ptr[(pt2.x + r) * src2.cols * src2_cn + (pt2.y + c) * src2_cn + l];
 
                nSum1 += t1;
                nSum2 += t2;
                nSqr1 += t1 * t1;
                nSqr2 += t2 * t2;
            }
        }
    }
 
    int nPixels = (patch_size * 2 + 1) * (patch_size * 2 + 1); // pixel num
    float fMean1 = (float)nSum1 / (float)nPixels;
    float fMean2 = (float)nSum2 / (float)nPixels;
    float fVar1 = (float)nSqr1 / (float)nPixels - (float)fMean1 * (float)fMean1;
    float fVar2 = (float)nSqr2 / (float)nPixels - (float)fMean2 * (float)fMean2;
 
    // NCC
    float fSumNCC = 0.0f;
 
    for (int r = -patch_size; r <= patch_size; r++)
    {
        for (int c = -patch_size; c <= patch_size; c++)
        {
            for (int l = 0; l < src1_cn; l++)
            {
                fSumNCC += (float)((src1_ptr[(pt1.x + r) * src1.cols * src1_cn + (pt1.y + c) * src1_cn + l]) - fMean1) 
                    * ((src2_ptr[(pt2.x + r) * src2.cols * src2_cn + (pt2.y + c) * src2_cn + l]) - fMean2);
            }
        }
    }
 
    return fSumNCC / (fVar1 * fVar2);
}
 
int main()
{
    Mat img, img2;
    img = imread("img/flower.jpg", 1);
    img2 = imread("img/flower.jpg", 1);
 
    int result_SSD = SSD(img, img2, Point(100, 100), Point(100, 100), 3);
    int result_SAD = SAD(img, img2, Point(100, 100), Point(100, 100), 3);
    float result_NCC = NCC(img, img2, Point(100, 100), Point(100, 100), 3);
 
    cout << "SSD = " << result_SSD << endl;
    cout << "SAD = " << result_SAD << endl;
    cout << "NCC = " << result_NCC << endl;
 
    namedWindow("image");
    imshow("image", img);
    waitKey();
 
    destroyAllWindows();
 
    return 0;
}