It seeeeeez! - Computer Vision with OpenCV

A (more scientific) little workshop on computer vision with C++/OpenCV.

Transcript

1. It seeeeeez!
   Computer Vision with OpenCV
   Marcel Neidinger
   Department of Mathematics and Computer Science,
   University of Basel
   April 27, 2017
   

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2. Derivation of Gradient Form for Images
   Introduce transformation V : R3 → R2
   (
   3
   x
   )
   yt →
   (
   2
   x − v1t
   )
   y − v2t (1)
   Rewrite I(x, y, t) = ˜
   I(V(x, y, t)) and use chain-rule for
   derivative
   gradI(x, y, t) = grad˜
   I(x − v1t, y − v2t) ·
   (
   1 0 −v1
   0 1 −v2
   )
   (2)
   We search for ∂I
   ∂t
   → third component
   ∂I
   ∂t
   = −
   (
   v1
   ·
   ∂I
   ∂x
   + v2
   ∂I
   ∂y
   )
   = −(grad˜
   I ·⃗
   v) (3)
   It seeeeeez! Computer Vision with OpenCV 2 / 1
   

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3. Derivation of Gradient Form for Images
   Introduce transformation V : R3 → R2
   (
   3
   x
   )
   yt →
   (
   2
   x − v1t
   )
   y − v2t (1)
   Rewrite I(x, y, t) = ˜
   I(V(x, y, t)) and use chain-rule for
   derivative
   gradI(x, y, t) = grad˜
   I(x − v1t, y − v2t) ·
   (
   1 0 −v1
   0 1 −v2
   )
   (2)
   We search for ∂I
   ∂t
   → third component
   ∂I
   ∂t
   = −
   (
   v1
   ·
   ∂I
   ∂x
   + v2
   ∂I
   ∂y
   )
   = −(grad˜
   I ·⃗
   v) (3)
   It seeeeeez! Computer Vision with OpenCV 2 / 1
   

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4. OpenCV is practical
   It seeeeeez! Computer Vision with OpenCV 3 / 1
   

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5. OpenCV: History
   Started at Intel Research
   Cross-plattform library for CV
   Today: More then a CV Library (machine learning)
   It seeeeeez! Computer Vision with OpenCV 4 / 1
   

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6. Programming OpenCV
   + =
   It seeeeeez! Computer Vision with OpenCV 5 / 1
   

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7. Programming OpenCV
   + =
   It seeeeeez! Computer Vision with OpenCV 5 / 1
   

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8. Programming OpenCV
   + =
   It seeeeeez! Computer Vision with OpenCV 5 / 1
   

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9. Programming OpenCV
   + =
   It seeeeeez! Computer Vision with OpenCV 5 / 1
   

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10. Programming OpenCV
    OpenCV is polygamous.
    - Florian Spiess
    It seeeeeez! Computer Vision with OpenCV 6 / 1
    

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11. Programming OpenCV
    OpenCV is polygamous.
    - Florian Spiess
    We will still use C++ in this workshop.
    Why?
    It’s the root language of OpenCV(fastest)
    Most examples are in C++(followed by python)
    It seeeeeez! Computer Vision with OpenCV 6 / 1
    

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12. Programming OpenCV
    OpenCV is polygamous.
    - Florian Spiess
    We will still use C++ in this workshop.
    Why?
    It’s the root language of OpenCV(fastest)
    Most examples are in C++(followed by python)
    I’m a c++ fanboy and this is my workshop
    It seeeeeez! Computer Vision with OpenCV 6 / 1
    

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13. Loading an image
    #include
    int main(int argc, char** argv)
    {
    cv::Mat img;
    img = cv::imread(argv[1]);
    }
    It seeeeeez! Computer Vision with OpenCV 7 / 1
    

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14. Displaying the image
    [...]
    cv::namedWindow(”debug”, cv::CV_WINDOW_AUTOSIZE);
    imshow(”debug”, img);
    while( true )
    {
    if( cv::waitKey(0) != −1 )
    {
    break;
    }
    }
    It seeeeeez! Computer Vision with OpenCV 8 / 1
    

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15. Theory: Segmenting images
    It seeeeeez! Computer Vision with OpenCV 9 / 1
    

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16. Segementation in OpenCV
    // Create new image to store greyscale
    cv::Mat imgGray, imgThresh;
    cv::cvtColor( img, imgGray, cv::CV_BGR2GRAY );
    // Threshold
    int value = 20;
    int maxval = 255;
    cv::threshold( imgGray, imgThresh, value, maxval,
    cv::THRESH_BINARY);
    dst(x, y) =
    {
    maxval, if src(x, y) > value
    0, else
    (4)
    It seeeeeez! Computer Vision with OpenCV 10 / 1
    

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17. OpenCV: Finding contours
    std::vector > contours;
    std::vector hierarchy;
    cv::findContours( imgThresh, contours, hierarchy,
    CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, cv::
    Point(0,0) );
    It seeeeeez! Computer Vision with OpenCV 11 / 1
    

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18. OpenCV: Practical example
    Enough examples.
    Let’s write a tennis ball
    tracker
    It seeeeeez! Computer Vision with OpenCV 12 / 1
    

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19. OpenCV: And moving images?
    VideoCapture cap(0);
    if( !cap.isOpened() )
    {
    return −1;
    }
    for(;;)
    {
    Mat frame;
    cap >> frame;
    // Treat like normal picture
    }
    It seeeeeez! Computer Vision with OpenCV 13 / 1
    

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20. Beyond the scope
    This barely scratched the surface of what OpenCV can do
    Advanced object detection
    Advanced feature selection
    Advanced tracking and object recognition methods
    Video analysis capabilities
    Machine Learning Capabilities(Boosting, Cascaders, k-nearest
    Neighbor …)
    Support for OpenCL and CUDA
    Integration into e.g. TensorFlow
    It seeeeeez! Computer Vision with OpenCV 14 / 1
    

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21. Beyond the scope
    This barely scratched the surface of what OpenCV can do
    Advanced object detection
    Advanced feature selection
    Advanced tracking and object recognition methods
    Video analysis capabilities
    Machine Learning Capabilities(Boosting, Cascaders, k-nearest
    Neighbor …)
    Support for OpenCL and CUDA
    Integration into e.g. TensorFlow
    Theorem
    Rule of Thumb: If there is an algorithm in computer vision,
    OpenCV has a highly optimized implementation readily available.
    It seeeeeez! Computer Vision with OpenCV 14 / 1
    

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22. Questions?
    

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