Disparity map colors are backwards in opencv

Question

My problem is that the colors in my disparity map are backwards. As in the farther away things are lighter than the things closer to the camera.

I have tried many things (i.e. convertTo, convertScaleAbs, and various combinations of values in them, etc.) and cannot seem to get the colors in the disparity map to reverse (i.e. be normal - where things closer are lighter than things farther away).

I need some help in doing that.

Also, out of curiosity, how can i change the color space of the disparity map to be like the colorful ones in MATLAB that I see online?

Here's my code and also on pastebin. http://pastebin.com/E3vVN6UU

#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/calib3d/calib3d.hpp>
#include <iostream>
#include <string>

using namespace cv;
using namespace std;

void show(const char* windowname, Mat image)
{
    namedWindow(windowname, CV_WINDOW_AUTOSIZE);
    imshow(windowname, image);
}

int main()
{ 
    Mat image1, image2;

    Mat camMat1 = (Mat_<double>(3,3) << 793.1338, 0, 337.2309, 0, 792.0555, 256.9991, 0, 0, 1);
    Mat camMat2 = (Mat_<double>(3,3) << 799.1271, 0, 319.8581, 0, 797.2460, 243.4638, 0, 0, 1);
    Mat dispCoeffs1 = (Mat_<double>(1,5) << 0.0033, -0.1320, -0.0019, 0.0026, 0);
    Mat dispCoeffs2 = (Mat_<double>(1,5) << -0.0109, -0.0188, -0.0014, -0.0055, 0);
    Mat RotMat = (Mat_<double>(3,3) << 0.9998, -0.0023, 0.0221, 0.0022, 1, 0.0031, -0.0221, -0.0031, 0.9998);
    Mat TransMat = (Mat_<double>(3,1) << 374.2306, -1.8319, 5.5745);

    //Rectify 
    Mat R1, R2, P1, P2, Q;
    stereoRectify(camMat1, dispCoeffs1, camMat2, dispCoeffs2, Size(640,480), RotMat, TransMat, R1, R2, P1, P2, Q, CV_CALIB_ZERO_DISPARITY, 1, Size(640,480));

    //Define the mapping to the done
    Mat rx1, ry1;
    Mat rx2, ry2;
    initUndistortRectifyMap(camMat1, dispCoeffs1, R1, P1, Size(640,480), CV_16SC2, rx1, ry1);
    initUndistortRectifyMap(camMat2, dispCoeffs2, R2, P2, Size(640,480), CV_16SC2, rx2, ry2);

    //SET THE BM STATE VARIABLES BEGIN - DONE GLOBALLY
    StereoBM bm;
    bm.state->preFilterSize = 31;
    bm.state->preFilterCap = 63;
    bm.state->SADWindowSize = 9;
    bm.state->minDisparity = -128;
    //bm.state->disp12MaxDiff = 2;
    bm.state->numberOfDisparities = 128;
    bm.state->textureThreshold = 50;
    bm.state->uniquenessRatio = 15;
    bm.state->speckleWindowSize = 100;
    bm.state->speckleRange = 16;
    //SET THE BM STATE VARIABLES END

    VideoCapture cap3 = VideoCapture(0);
    VideoCapture cap4 = VideoCapture(1);

    //cap3.set(CV_CAP_PROP_FRAME_WIDTH, 320);
    //cap3.set(CV_CAP_PROP_FRAME_HEIGHT, 240);
    //cap4.set(CV_CAP_PROP_FRAME_WIDTH, 320);
    //cap4.set(CV_CAP_PROP_FRAME_HEIGHT, 240);

    cap3 >> image1;
    cap4 >> image2;
    Size imageSize = image1.size();

    Mat gray_image1;
    Mat gray_image2;
    Mat frame1r;
    //frame1r.create(image1.size(), CV_8U);
    Mat frame2r;
    //frame2r.create(image2.size(), CV_8U);
    Mat frame1rf;
    Mat frame2rf;
    //Mat disp(image1.size(), CV_16S);
    //Mat vdisp(image1.size(), CV_8U);
    Mat disp, vdisp;
    //Mat image3d(image1.size(), CV_32FC3);
    Mat image3d;
    Mat rectified_pair;
    rectified_pair.create(imageSize.height, (imageSize.width)*2, CV_8UC3);

    //Actually do the mapping -- based on the mapping definition

    while(1)
    {
        bm.state->preFilterSize = 31;
        bm.state->preFilterCap = 63;
        bm.state->SADWindowSize = 21;
        bm.state->minDisparity = -128;
        //bm.state->disp12MaxDiff = 2;
        bm.state->numberOfDisparities = 64;
        bm.state->textureThreshold = 20;
        bm.state->uniquenessRatio = 10;
        bm.state->speckleWindowSize = 100;
            bm.state->speckleRange = 32;

        cvtColor(image1, gray_image1, CV_BGR2GRAY);
        cvtColor(image2, gray_image2, CV_BGR2GRAY);
        remap(gray_image1, frame1r, rx1, ry1, CV_INTER_LINEAR);
        remap(gray_image2, frame2r, rx2, ry2, CV_INTER_LINEAR);
        bm(frame1r, frame2r, disp);
        normalize(disp, vdisp, 0, 255, NORM_MINMAX, CV_8U);
        //convertScaleAbs(vdisp, vdisp, 1, 0);
        disp.convertTo(vdisp, CV_8U, 255/(64*16.));
        show("disparity", vdisp);
        //reprojectImageTo3D(disp, image3d, Q, true);
        //show("depth map", image3d);

        //display image side by side for rectified window
        //copy frame1r to the left side
        cvtColor(frame1r, frame1rf, CV_GRAY2BGR);
        frame1rf.copyTo(rectified_pair(Rect(0,0,imageSize.width, imageSize.height)));
        //copy frame2r to the right side
        cvtColor(frame2r, frame2rf, CV_GRAY2BGR);
        frame2rf.copyTo(rectified_pair(Rect(imageSize.width,0,imageSize.width, imageSize.height)));
        for(int i=0; i<imageSize.height; i+=32)
            line(rectified_pair, Point(0,i), Point((imageSize.width)*2, i), CV_RGB(0,255,0));
        show("rectified", rectified_pair);

        cap3 >> image1;
        cap4 >> image2;
        if(waitKey(15) == 27)
            break;
    }

    return 0;
}

Answer 1

I was facing the same problem then I tried swapping right and left images,and it worked! Now I am getting correct image.

Answer 2

I'm not using stereo pairs but get the same result using Kinect - far = light, near = dark To change this I have used the below :

  double min, max;
  minMaxLoc(depthImage, &min, &max);

  depthImage.convertTo(rImage, CV_8U, -255.0/max, 255);