TVL1 Optical flow - TVL1 Optical flow

The tvl1 function is used for Optical flow application and its formulation is based on Total Variation (TV) regularization & the robust L1 normalization in the data fidelity term. TVL1 algorithm preserves discontinuties in the flow field and increases robustness against occlusions, illumination changes and noise.

Public member functions

    // Compute optical flow for previous two frames &
    // read current frame to create image pyramid.
    // First two calc function call will create image
    // pyramid only and flow vector won't be computed.
    // From third calc function call, it will give flow
    // vector by processing previous two frame.
    calc( cv::Mat current_frame, Mat_<Point2f> flow)

    //get tau paramter
    getTau()

    //get lambda paramter
    getLambda()

    //get theta paramter
    getTheta()

    //get nscales parameter
    getScalesNumber()

    //get warps parameter
    getWarpingsNumber()

    //get epsilon parameter
    getEpsilon()

    //get innnerIterations parameter
    getInnerIterations()

    //get outerIterations parameter
    getOuterIterations()

    //get scaleStep parameter
    getScaleStep()

    //get gamma parameter
    getGamma()

    //get medianFiltering parameter
getMedianFiltering()

    //get UseInitialFlow parameter
getUseInitialFlow()

    //set tau paramter
    setTau(double val)

    //set lambda paramter
setLambda(double val)

    //set theta paramter
setTheta(double val)

    //set nscales parameter
setScalesNumber(int val)

    //set warps parameter
setWarpingsNumber(int val)

    //set epsilon parameter
setEpsilon(double val)

    //set innnerIterations parameter
setInnerIterations(int val)

    //set outerIterations parameter
setOuterIterations(int val)

    //set scaleStep parameter
setScaleStep(double val)

    //set gamma parameter
setGamma(double val)

    //set medianFiltering parameter
setMedianFiltering(int val)

    //set UseInitialFlow parameter
setUseInitialFlow(bool val)

Static public member functions

static Ptr xf::cv::DualTVL1OpticalFlow::create( double tau = 0.25,
                                                double lambda = 0.15,
                                                double theta = 0.3,
                                                int nscales = 5,
                                                int warps = 5,
                                                double epsilon = 0.01,
                                                int innnerIterations = 30,
                                                int outerIterations = 10,
                                                double scaleStep = 0.8,
                                                double gamma = 0.0,
                                                int medianFiltering = 5,
                                                bool UseInitialFlow = false)

Parameter Descriptions

The following table describes the template and the function parameters.

Table 752 Table . TVL1 Parameter Description
Parameter	Description
current_frame	Grey scale input image
flow	Computed flow image that has the same size as input image and type CV_32FC2.
tau	Time step of the numerical scheme. Default value is 0.25
lambda	Weight parameter for the data term, attachment parameter. Default value is 0.15
theta	Weight parameter for (u - v)^2, tightness parameter. Default value is 0.3
nscales	Number of scales used to create the pyramid of images. Default value is 5
warps	Number of warpings per scale. Default value is 5
epsilon	Stopping criterion threshold used in the numerical scheme, which is a trade-off between precision and running time.Default values is 0.01
innnerIterations	Inner iterations (between outlier filtering) used in the numerical scheme. Default value is 30
outerIterations	Outer iterations (number of inner loops) used in the numerical scheme. Default value is 10
scaleStep	Step between scales (<1). Default value is 0.8
gamma	coefficient for additional illumination variation term. Only gamma = 0.0 is supported
medianFiltering	MedianBlur Filter size. Only filter size = 5 is supported.
UseInitialFlow	Use initial flow. Supported value is false

Resource Utilization

The following table summarizes the resource utilization in different configurations, generated using Vitis HLS 2022.1 tool for the xcu50-fsvh2104-2-e FPGA.

Table 753 Table . TVL1 Function Resource Utilization Summary
Operating Mode	Operating Frequency (MHz)	Utilization Estimate
Operating Mode	Operating Frequency (MHz)	BRAM_18K	DSP_48Es	FF	LUT
2 Pixel	300	408	931	246513	220169

Performance Estimate

The following table summarizes the performance of the kernel in 2-pixel mode as generated using Vitis HLS 2022.1 tool for the Xilinx xcu50-fsvh2104-2-e FPGA to process a grayscale 384x288 image image.

Table 754 Table . TVL1 Function Performance Estimate Summary
Operating Mode	Latency Estimate
Operating Mode	Max Latency (ms)
2 pixel operation (300 MHz)	95.6

TVL1 Optical flow - TVL1 Optical flow - 2023.2 English

Vitis Libraries