Home/ Questions/Q 6767737
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-26T14:59:14+00:00

I cannot successfully calculate the distance transformation using OpenCV (2.3) on an ubuntu. The

  • 0

I cannot successfully calculate the distance transformation using OpenCV (2.3) on an ubuntu. The output is either black or a copy of the orignial image, but never as expected an greyscale image with gradients.

My code:

Mat input(Size(100,100), CV_8UC1);
circle(input, Point(50,50), 10 Scalar(255,255,255), 15, 0, 0));

Mat output(Size(100,100), CV_32FC1);
distanceTransformation(input, output, CV_DIST_L2, CV_DIST_MASK_3); //Output is completely black
//distanceTransformation(input, output, CV_DIST_L2, CV_DIST_MASK_PRECISE); //Output is a "copy" of input


imshow("in", input);
imshow("out", output);

Any suggestions?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    The first call is correct, but being a distance, it’s not stored as uchar. When you want to display it, OpenCV converts those float (i think) into uchars. And the result seems black.

    Find the max value in the output, and then scale it to fit a grayscale image

    double maxVal = findMaxDistanceSomehow(); 

output.convertTo( displayBuffer, CV_8UC1, 255./maxVal,0);

imshow("dist", displayBuffer);

    EDIT

    The first idea was correct, but you actually did not try to find maxVal! You said that by looking at the picture, instead of actually extracting it. Difference between win and fail.

    So, calculate the dist transform using the precise algoritm, and then 

    output.convertTo( displayBuffer, CV_8UC1, 10 ,0);

    Edit 2

    And you must put the setTo(0) there.

    • 0