MATLAB: Difference between “Canny” and “Canny_old” in Image Processing toolbox function “edge”

cannycanny_oldedgeImage Processing ToolboxMATLABopencv

Hi,

I was trying to compare OpenCV and Matlab outputs a given test image for Canny edge function and I realized that the "edge" function in matlab provides a "canny" and a "canny_old" implementations.

Can you please provide some reference as to the math behind it and what is the difference between the two?

Thanks & Regards,

Mazhar

Best Answer

Mazhar:

Apologies for such a delayed response. As far as I know, 'canny_old' does not have any relation to the openCV implementation. I would encourage you to avoid using canny_old, as it probably exists only for backward compatibility reasons.

openCV does not use a derivative of gaussian for gradient computations, whereas the MATLAB version does so. Additionally, the use of bwselect in the sub-function 'thinAndThreshold' makes the MATLAB results better looking than the openCV equivalent.

See this post for additional details: https://dsp.stackexchange.com/questions/4716/differences-between-opencv-canny-and-matlab-canny

Are you trying to get the same results that MATLAB provides, using openCV? Could you elaborate on how you are trying to do so?

Related Solutions

MATLAB: Canny’s Edge Detection

Calculate the circularity:

measurements = regionprops(labeledImage, 'area', 'Perimeter');
allAreas = [measurements.Area];
appPerimeters = [measurements.Perimeter];
circularities = appPerimeters .^2 ./ (4*pi*allAreas);

If it's round, the circularity will be below 2-3 or so. For a perfect circle the circularity is 1. Higher values will be for less round objects with more tortuous borders.

MATLAB: Adaptive Canny edge detection

Canny edge detection is accomplished using the edge function. Matlab will get "automatic/adaptive" thresholds if you don't specify thresholds as an argument. An easy way to implement this is to simply call Edge twice; first to get an initial capture of the thresholds, then to adjust thresholds as needed based on the automatic thresholds.

[~,threshOut = edge(I,'Canny');
threshold = threshOut*1.0;
BW1 = edge(I,'Canny',threshold);

Just adjust the multiplier to adjust thresholds. Matlab's adaptive technique is fairly straightforward, and I believe it is a variant of the Otsu method; they simply throw out 70% of the detected edge pixels for the high threshold, and the low threshold is some constant factor multiplied by the high threshold.

There are a number of other self-adaptive ways to choose Canny thresholds, a few are detailed here: http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=5476095

Best Answer

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MATLAB: Canny’s Edge Detection

MATLAB: Adaptive Canny edge detection

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