Canny Edge Detector

Code Snippets

The Canny edge detector facilitates:

• Good detection: finds all edges
• Good localization: the found edges are as close as possible to the "real" edges in the image
• Minimal response: one edge response is accepted for each position, i.e. avoiding multiple close or intersecting edge responses

The EasyImage Canny edge detector operates on a grayscale BW8 image and delivers a black-and-white BW8 image where pixels have only 2 possible values: 0 and 255. Pixels corresponding to edges in the source image are set to 255; all others are set to 0. It can adjust the scale analysis, it doesn't allow sub-pixel interpolation and it delivers a binary image after thresholding.

Canny edge detector example

The Canny edge detector requires only two parameters:

• Characteristic scale of the features of interest: the standard deviation of the Gaussian filter used to smooth the source image.
• Gradient threshold with hysteresis: maximum magnitude of the gradient of the source image expressed as a fraction ranging from 0 to 1 (two values).

The API of the Canny edge detector is a single class, ECannyEdgeDetector, with the following methods:

• Apply: applies the Canny edge detector on an image/ROI.
• GetHighThreshold: returns the high hysteresis threshold to consider that a pixel is an edge.
• GetLowThreshold: returns the low hysteresis threshold to consider that a pixel is an edge.
• GetSmoothingScale: returns the scale of the features of interest.
• GetThresholdingMode: returns the mode of the hysteresis thresholding.
• ResetSmoothingScale: prevents the smoothing of the source image by a Gaussian filter.
• SetHighThreshold: sets the high hysteresis threshold to consider that a pixel is an edge.
• SetLowThreshold: sets the low hysteresis threshold to consider that a pixel is an edge.
• SetSmoothingScale: sets the scale of the features of interest.
• SetThresholdingMode: sets the mode of the hysteresis thresholding.

The result image must have the same dimensions as the input image.