Can I set the maximum displacement for opticalflow?

Hi, I am using optical flow to compute sea surface current speed using satellite data.

But, the results of opticalflow show the overestimated current speed rather than known speed current.

So I want to set the maximum displacement of pixels (e.g. not over 5 pixel).

Can I set the maximum displacement for opticalflow method?

Answer 1

[Ayush]

Hi,

You can follow the below steps as a workaround to set the maximum displacement for the optical flow:

1. Find the horizontal and vertical flow components for each pixel using the optical flow function.
2. Calculate the magnitude of displacement for each pixel using the horizontal and vertical components. This gives you the speed at each pixel.
3. For pixels where the displacement magnitude exceeds your threshold (e.g., 5 pixels), you can scale down the Vx and Vy components to meet your maximum displacement criterion.

Refer to the pseudo code below for a better understanding:

% Assuming 'opticFlow' is your computed optical flow object and 'I' is the current frame
flow = estimateFlow(opticFlow, I);

% Get the horizontal and vertical flow components
Vx = flow.Vx;
Vy = flow.Vy;

% Calculate the magnitude of displacement
displacementMagnitude = sqrt(Vx.^2 + Vy.^2);

% Define your maximum displacement threshold
maxDisplacement = 5;

% Find pixels where the displacement exceeds the maximum allowed
exceedsThreshold = displacementMagnitude > maxDisplacement;

% Scale down the Vx and Vy components for these pixels
Vx(exceedsThreshold) = Vx(exceedsThreshold) .* (maxDisplacement ./ displacementMagnitude(exceedsThreshold));
Vy(exceedsThreshold) = Vy(exceedsThreshold) .* (maxDisplacement ./ displacementMagnitude(exceedsThreshold));

% Now, Vx and Vy have been adjusted to ensure no displacement exceeds the maximum threshold

For more information on the "estimateFlow" function, refer to the below documentation:

https://www.mathworks.com/help/vision/ref/opticalflowhs.estimateflow.html