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Error in Watershed Distance Transform [closed]

asked 2018-11-26 08:59:32 -0500

nicoz gravatar image

updated 2018-11-26 10:09:57 -0500

I'm trying to execute image segmentation with distance transform and watershed algorithm. I've used GrabCut to eliminate the background. After several tests, I found the error in this part:

 // Perform the distance transform algorithm
Mat dist;
distanceTransform(bw, dist, DIST_L2, 3);
// Normalize the distance image for range = {0.0, 1.0}
// so we can visualize and threshold it
normalize(dist, dist, 0, 1.0, NORM_MINMAX);
imshow("Distance Transform Image", dist);

I'm using Codeblocks, Ubuntu 18.04 and OpenCV 4.0.0.

The little part of the code above is from this tutorial:

I get this error:

terminate called after throwing an instance of ‘cv::Exception'

what(): OPenCV(4.0.0) /home/nicolas/opencv-4.0.0/sources/modules/highgui/src/window_gtk.cpp:146: error: (-215:Assertion failed) == widget->original_image->data.ptr in function ‘cvlmageWidgetSetImage'
Aborted (core dumped)

Process returned 134 (0x86) execution time : 3.122 s Press ENTER ti continue.

Does anyone knows what's happening?

EDIT 1: Berak's answer solved the problem above, thanks berak! But after I've got another error in this part:

// Create the marker image for the watershed algorithm Mat markers = Mat::zeros(dist.size(), CV_8U);//CV_32SC1);

// Draw the foreground markers for (size_t i = 0; i < contours.size(); i++) drawContours(markers, contours, static_cast<int>(i), Scalar::all(static_cast<int>(i)+1), -1);

// Draw the background marker circle(markers, Point(5,5), 3, CV_RGB(0,255,0), -1); imshow("Markers", markers*10000);

I replaced CV_32SC1 with CV_8U and it worked, but I don't know if it's the right solution. After I got another error in this part:

// Perform the watershed algorithm watershed(src, markers); Mat mark = Mat::zeros(markers.size(), CV_8UC1); markers.convertTo(mark, CV_8UC1); bitwise_not(mark, mark); imshow("Markers_v2", mark); // uncomment this if you want to see how the mark waitKey(); // image looks like at that point

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Closed for the following reason the question is answered, right answer was accepted by nicoz
close date 2018-11-26 11:08:55.816621


would you be so nice, and replace the error screenshot with a TEXT version, so it can be quoted / indexed properly ? thank you !

berak gravatar imageberak ( 2018-11-26 09:08:34 -0500 )edit

Yes, sure! It's ok the way I did it?

nicoz gravatar imagenicoz ( 2018-11-26 09:53:03 -0500 )edit

sure, thanks a lot !

berak gravatar imageberak ( 2018-11-26 09:55:06 -0500 )edit

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answered 2018-11-26 09:15:26 -0500

berak gravatar image

this is most likely a bug introduced here

there is already a fix for Qt from nov. 16, and another pr here

you'll have to update your opencv codebase, and rebuild, but for today, try to convert the image back to CV_8U, before using imshow() like:

normalize(dist, dist, 0, 255.0, NORM_MINMAX, CV_8U);
imshow("Distance Transform Image", dist);
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Thanks a lot, berak! This solved the problem, but now I found another error. I'll edit the question with it.

nicoz gravatar imagenicoz ( 2018-11-26 09:54:28 -0500 )edit

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Asked: 2018-11-26 08:59:32 -0500

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Last updated: Nov 26 '18