Dawit's profile - activity

Ok. Thanks.

if you are familiar with it could you help me with this :) http://answers.opencv.org/question/33589/dense-optical-flow-dualtvl1-in-ndk/

ok didn't see the date.

i want to compute Dense Optical Flow using OpenCV android NDK but i can only find Video.calcOpticalFlowFarneback dense optical flow function which doesn't give me the result i want.

anyone who can tell me how to find createOptFlow_DualTVL1() function in Android NDK. i am using OpenCV-2.4.5-android-sdk.

Thanks in advance

Mat New_Previous_Gray (holds the previous image)
Mat New_Current_Gray (holds the current image)
Mat_<Point2f> Optical_Flow;
Ptr<DenseOpticalFlow> tvl1 = createOptFlow_DualTVL1();  
tvl1->calc(New_Previous_Gray, New_Current_Gray, Optical_Flow); 
for(int y = 0; y < Optical_Flow.cols; y++)
{
   for(int x = 0; x < Optical_Flow.rows; x++)
   {
      const Point2f& flow_xy = Optical_Flow.at<Point2f>(x, y);
      int Vel_x = flow_xy.x;
      int Vel_y = flow_xy.y;
      Pxl_Distance = sqrt(double(((abs(Vel_x) * abs(Vel_x)) + (abs(Vel_y) * abs(Vel_y)))));
   }
}

so i could get the velocity for every pixel in "Pxl_Distance".

hope this sample code is clear cheers.

I have used DualTV1 actually i'm still using it since i need to compute dense optical flow (velocty of every pixel). As far i know using DualTV1 for real time (10fps)is quite impossible in standard computer since it is compute the velocity if every pixel for every frame. here is what some one advice me if it helps.

http://stackoverflow.com/questions/19309567/speeding-up-optical-flow-createoptflow-dualtvl1

I have implemented dense optical flow to compute the velocity of every pixel in c++ using OpenCV 2.4.8 previously. This example helps me a lot (https://github.com/Itseez/opencv/blob/master/samples/cpp/tvl1_optical_flow.cpp). Now I want to convert my code to javaCV but i could’t. my code in c++ using OpenCV is like this:

Mat New_Previous_Gray (holds the previous image)
Mat New_Current_Gray (holds the current image)
Mat_<Point2f> Optical_Flow;
Ptr<DenseOpticalFlow> tvl1 = createOptFlow_DualTVL1();  
tvl1->calc(New_Previous_Gray, New_Current_Gray, Optical_Flow); 
for(int y = 0; y < Optical_Flow.cols; y++)
{
   for(int x = 0; x < Optical_Flow.rows; x++)
   {
      const Point2f& flow_xy = Optical_Flow.at<Point2f>(x, y);
      int Vel_x = flow_xy.x;
      int Vel_y = flow_xy.y;
      Pxl_Distance = sqrt(double(((abs(Vel_x) * abs(Vel_x)) + (abs(Vel_y) * abs(Vel_y)))));
   }
}

so i could get the velocity for every pixel in "Pxl_Distance".

Now I want to do the same thing in JavaCv but so far what what i could do is:

CvMat pFrame = pFrameGray.asCvMat();
CvMat cFrame = pFrameGray.asCvMat();
CvMat flow = Flowipl.asCvMat();
cvConvertImage(pFrame, pFrame, CV_CVTIMG_FLIP);
cvConvertImage(cFrame, cFrame, CV_CVTIMG_FLIP);
cvConvertImage(flow, flow, CV_CVTIMG_FLIP); 
DenseOpticalFlow tvl1 = createOptFlow_DualTVL1();
tvl1.calc(pFrame, cFrame, flow);

But when i view the pixel values of "flow"(CvMat) all are 0. i don't know what i have done wrong or if am doing it right when i compute the DenseOpticalFlow in the first place. i need help. i already spend too much time on this. Thanks in advance.

Hello, did you manage to solve this issue? I'm having the same problem.

_flow->getDouble("tau"); // to get the value _flow->set("tau",0.125); // to change the value

Cheers

I am having the same problem. did you find any solution?