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calcOpticalFlowSF() doesn't respond

asked 2013-10-02 07:51:49 -0500

Hi,

I try to use the calcOpticalFlowSF() function, but when I launch it, the programm doesn't repond, here the part of the code that use it:

 frame1 = cv::imread("frame10.png");
frame2 = cv::imread("frame11.png");

if (frame1.empty()) {
   cout<<"could not read image oldori"<<endl;

      return;
    }

    if (frame2.empty()) {
       cout<<"could not read image ori"<<endl;
      return;
    }

    if (frame1.rows != frame2.rows && frame1.cols != frame2.cols) {
         cout<<"images should be of equal sizes "endl;
      return;
    }

    if (frame1.type() != 16 || frame2.type() != 16) {
         cout<<"images should be of equal type CV_8UC3")endl;
      return;
    }

cv::Mat flow;

cv::calcOpticalFlowSF(frame1, frame2, flow, 2, 2, 4);
// calcOpticalFlowSF(frame1, frame1,  // doesn't work too.
//                    flow,
//                    3, 2, 4, 4.1, 25.5, 18, 55.0, 25.5, 0.35, 18, 55.0, 25.5, 10);

I know that the error come from the function calcOpticalFlowSF, because if I comment it, the programm works. I use the same pictures as they use in the SimpleFlow demo.

Do you have an idea why it doesn't work?

thanks,

best regards.

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Did you find the reason for this?

Tharindu gravatar imageTharindu ( 2014-07-01 22:35:32 -0500 )edit

1 answer

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answered 2014-08-04 10:52:58 -0500

erenik gravatar image

updated 2014-08-04 10:54:58 -0500

Not sure if this is a valid answer, but I had some problems with this function as well and took my time to do some testing on it, using just initialized cv::Mats with specified sizes and CV_8UC3 type.

What I found was that the time complexity of this function seems off the scales (at least in the CV version I am currently using). Size is the width and height of the matrix.

Size  Time in Milliseconds
4      20
8      100
16    400~500
32    2100~2200

The code could be simplified to something like the following:

int size = 16;
cv::Mat lastFrame, frame, flow;
frame = cv::Mat(size, size, CV_8UC3);
frame.copyTo(lastFrame);
cv::calcOpticalFlowSF(lastFrame, frame,
    flow,
    3, 2, 4, 4.1, 25.5, 18, 55.0, 25.5, 0.35, 18, 55.0, 25.5, 10);

I'm guessing there is some issue with the code base, or that it was meant to be used on the GPU with parallel computing. I have tried both the calcOpticalFlowPyrLK and calcOpticalFlowFarneback methods, and they work without problems. From what I've seen this "SimpleFlow" might not be suitable for real-time analysis, but It could also be this specific implementation.

I noticed that the authors of the algorithm were talking in seconds, while using the algorithm on a GPU, which could be of relevance: http://graphics.berkeley.edu/papers/Tao-SAN-2012-05/

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Asked: 2013-10-02 07:51:49 -0500

Seen: 1,140 times

Last updated: Aug 04 '14