Variance.cpp

#include "Variance.h"
#include "LinearMapper.h"

namespace DirectGraphicalModels { namespace fex
{
Mat CVariance::get(const Mat &img, SqNeighbourhood nbhd)
{
    int             width   = img.cols;
    int             height  = img.rows;

    // Converting to one channel image
    Mat I;
    if (img.channels() != 1) cvtColor(img, I, cv::ColorConversionCodes::COLOR_RGB2GRAY);
    else img.copyTo(I);

    Mat res(img.size(), CV_8UC1);                                   
    Mat integralImg;                                                
    integral(I, integralImg);
    
    for (int y = 0; y < height; y++) {
        int      y0     = MAX(0, y - nbhd.upperGap);
        int      y1     = MIN(y + nbhd.lowerGap, height -1);
        byte    *pRes   = res.ptr<byte>(y);
        int *pI0    = integralImg.ptr<int>(y0);
        int *pI1    = integralImg.ptr<int>(y1 + 1);
        for (int x = 0; x < width; x++) {
            int     x0  = MAX(0, x - nbhd.leftGap);
            int     x1  = MIN(x + nbhd.rightGap, width - 1);
            int     S   = (x1 - x0 + 1) * (y1 - y0 + 1);
            float   med = static_cast<float>(pI1[x1 + 1] - pI1[x0] - pI0[x1 + 1] + pI0[x0]) / S;
            float   Sum = 0;
            for (int j = y0; j <= y1; j++) {
                byte *pImg = I.ptr<byte>(j);
                for (int i = x0; i <= x1; i++) {
                    float dif = static_cast<float>(pImg[i]) - med;
                    Sum += dif*dif;
                } // i
            } // j
            float val = sqrtf(Sum / S);
            pRes[x] = linear_mapper<byte>(val, 0, 100);
        } // x
    } // y

    return res; 
}
} }