Canny (OCL, 3-beta) can not detect connected contour of black square on a white background.

asked 2014-12-30 13:09:17 -0600

Vit
276 ●2 ●12 http://drvit.livejourn...

updated 2015-01-12 15:04:10 -0600

Simple code for simple image result is not connected contour as it is expected. Top or bottom edge missed. Result printscreen is square-bug.png . The picture itself is square.png. Code is:

   void test(){
        UMat img = imread("./square.png", IMREAD_COLOR).getUMat(ACCESS_READ);
        UMat imgGray, imgGrayEdges3, imgGrayEdges5;
        cvtColor(img, imgGray, CV_BGR2GRAY);
        Canny(imgGray, imgGrayEdges3, 50, 150, 3);
        Canny(imgGray, imgGrayEdges5, 300, 2000, 5); // why so large thresholds?..
        cout << imgGray.getMat(ACCESS_READ) << "\n" << imgGrayEdges3.getMat(ACCESS_READ) << "\n" << imgGrayEdges5.getMat(ACCESS_READ) ;
        imshow("img", img);
        imshow("canny3", imgGrayEdges3);
        imshow("canny5", imgGrayEdges5);
        waitKey();
    }

Am I doing something wrong?

I use OpenCV3-beta in Eclipse under Win8.1 and have to build source from git. Source updated and compiled today (last canny.cpp change was 7 weeks ago). I do have openCL so I guess UMat Canny function uses OCL_RUN version of function

UPDATE: device and system info

Driver Packaging
Version 14.501.1003-141120a-178000C
Catalyst Version 14.12 AMD Catalyst
Omega Software 2D Driver
Version 8.01.01.1443 Direct3D
Version 9.14.10.01080 OpenGL
Version 6.14.10.13283 Mantle Driver
Version 9.1.
- Graphics Chipset AMD Radeon HD 7900 Series
- BIOS Version 015.012.000.004
- BIOS Part Number 113-C3860100-100
- BIOS Date 2011/12/07

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Well.. no ideas. Bug reported: http://code.opencv.org/issues/4093

Vit ( 2015-01-07 04:19:50 -0600 )edit

Can you share on which hardware and driver this happen? Did you test with OpenCV 2.4? The code would be only slightly different, example:

    #include "opencv2/ocl/ocl.hpp"
    cv::Mat input = cv::imread(filename,0 ); //directly grayscale
    cv::ocl::oclMat imgGray(input);
    cv::ocl::oclMat imgGrayEdges3, imgGrayEdges5;

    cv::ocl::Canny(imgGray, imgGrayEdges3, 50, 150, 3);
    cv::ocl::Canny(imgGray, imgGrayEdges5, 300, 2000, 5);

    cv::imshow("img", (cv::Mat) imgGray);
    cv::imshow("canny3", (cv::Mat) imgGrayEdges3);
    cv::imshow("canny5", (cv::Mat) imgGrayEdges5);

Which works correctly for me by the way

Antonio ( 2015-01-12 09:06:47 -0600 )edit

BTW: The answer to: "Why so large threshold" is that when using 5 as kernel size of Canny, at an intermediate stage you get a Sobel image computed with the mask 5 parameters, which has much larger multipliers, and of course convolves a larger number of pixels.

Antonio ( 2015-01-12 09:55:36 -0600 )edit

@Antonio, thanks for your answer. I tested Canny and it is ok in 2.4 with this test picture, your code works perfect. The problem is actual for OpenCV3-beta only. Post updated by soft- and hardware info.

As for threshold, from my point of view it is more convenient to have normalized output i.e. threshold should not be a function of another parameters, this increases the code hidden-errors possibility.

Vit ( 2015-01-12 15:09:56 -0600 )edit

@Vit I confirm 100% your findings: OpenCV3 OpenCL implementation of Canny it's buggy. (Although is 4 times faster)

Antonio ( 2015-01-13 06:19:47 -0600 )edit

BTW, did you build 32bit or 64bit? In my case, 32bit

Antonio ( 2015-01-13 06:42:14 -0600 )edit

@Antonio, thanks for you informative report on OpenCV bug-tracker. I hope this will activate works on that issue. According to attached "cmake-gui-out.txt" file there I have 32-bit version.

Vit ( 2015-01-13 08:32:59 -0600 )edit

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answered 2014-12-30 20:55:15 -0600

Messina Vision Systems

56 ●1 ●2 http://www.messinasyst...

I just ran it through the sample code in this link and it worked fine for me.

They used: Canny(imgGray, imgGrayEdges, lowThreshold, lowThreshold*3, 3); where lowThreshold is a value between 0 to 100.

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How this this related to my question? It is not just Canny(..) function call, it is a bunch of different functions call, including blur(..) which affects to the input data for Canny. The most important this is not OpenCL UMat (which is the most attractive thing of OpenCV3) version of this code. I should emphasize on OCL aspect...

Vit ( 2014-12-31 03:09:10 -0600 )edit

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Canny (OCL, 3-beta) can not detect connected contour of black square on a white background.

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Canny (OCL, 3-beta) can not detect connected contour of black square on a white background.