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Asked: 2026-06-11T03:24:10+00:00

I need to figure out if any given pixel is black or white on

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I need to figure out if any given pixel is black or white on a gray-scale image that I put through a thresholding algorithm before that. The image becomes basically blobs of black on a white background.

Mat falsetest;

...

cv::cvtColor(detected_edges, falsetest, CV_BGR2GRAY);    
threshold(falsetest, falsetest,128, 255,THRESH_BINARY);

...

printf("x:%d y:%d %d\n",x,y,falsetest.at<uchar>(x,y));

I expected the results to be either 0 or 255, however, that is not the case. The output for different pixels looks something like this:

x:1259 y:175 111
x:1243 y:189 184
x:1229 y:969 203
x:293 y:619 255
x:1123 y:339 183

Am I trying to do this in a wrong way, or does it seem that the error lies elsewhere?

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1 Answer

  1. Editorial Team

    I have finally figured out what the problem was. I thought that when I called

    cv::cvtColor(detected_edges, falsetest, CV_BGR2GRAY);

    all the matrix data was copied to falsetest. However, it seems that it was not the case, and when I proceeded to modify detected_edges, falsetest also became contaminated. Cloning the matrix solved the problem.

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