CODEWITHSUNDEEP
c++opencvbrightness
alonsodub
alonsodub

Reputation: 23

Adjusting Brightness, OpenCV and c++

I wanted to know if there is any function of OpenCV using C++ to adjust the brightness and contrast of a video / frame. You can convert from BGR color space to HSV color space, and discard the latter component V (luminance) to make the algorithm less sensitive to light conditions in the video, but how can I do it?

I was thinking of using something like cvAddS (frame, cvScalar (-50, -50, -50), frame) to Decrease the brightness, cvAddS and cvScalar work's well for C but how can I do that for C++, I use AddS and Scalar in my program, but don't work with C++

int main() {
    VideoCapture video(1);
    if(!video.isOpened()) {
        cerr<<"No video input"<<endl; return -1;
    }
    namedWindow("Video",CV_WINDOW_AUTOSIZE);

    for(;;) {
        Mat frame;
        video >> frame; if(!frame.data) break;
        Mat frame2;
        //I USE AddS AND Scalar TO DECREASE THE BRIGHTNESS
        AddS(frame,Scalar(-50,-50,-50),frame2);
        //BUT DON'T WORK WITH C++
        imshow("Video",frame2);

        int c=waitKey(20);

        if(c >= 0)break;
    } 
}

Upvotes: 2

Views: 8784

Answers (2)

Adi Shavit
Adi Shavit

Reputation: 17295

Brightness and contrast are usually corrected using a linear transformation of the pixel values. Brightness corresponds to the additive shift and contrast corresponds to a multiplicative factor.

In general, given a pixel value v, the new value after to correction would be v'=a*v + b.

Upvotes: 3

flowfree
flowfree

Reputation: 16462

Use matrix expression:

cv::Mat frame2 = frame + cv::Scalar(-50, -50, -50);

You might also want to adjust the contrast with histogram equalization. Convert your RGB image to HSV and apply cv::equalizeHist() to the V channel.

Upvotes: 4

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