# cannyEdgeDetector() Applies the Canny edge-detection algorithm to an image. ``` class func cannyEdgeDetector() -> any CIFilter & CICannyEdgeDetector ``` ## Return Value A [`CIImage`](/documentation/CoreImage/CIImage) with the detected edges. ## Discussion This filter performs a Canny edge-detection on the input image, producing a black-and-white image with the detected edges. White pixels indicate an edge, and black pixels indicate no edge. The Canny edge-detection filter uses the following properties: - `inputImage`: The [`CIImage`](/documentation/CoreImage/CIImage) to use as an input for the effect. - `gaussianSigma`: A `float` specifying the sigma of the Gaussian blur to apply, reducing high-frequency noise. Defaults to `1.6`. - `perceptual`: A `Boolean` specifying whether to use a perceptual color space to compute the edge thresholds. Defaults to `false`. - `thresholdLow`: A `float` specifying the threshold for weak edges. Defaults to `0.02`. - `thresholdHigh`: A `float` specifying the threshold for strong edges. Defaults to `0.05`. - `hysteresisPasses`: The number of hysteresis passes to apply to promote weak edge pixels. Minimum value is `0`, maximum value is `20`, and defaults to `1`. The following code applies Canny edge-detection to an image: ```swift func cannyEdgeDetector(inputImage: CIImage) -> CIImage { let filter = CIFilter.cannyEdgeDetector() filter.inputImage = inputImage filter.gaussianSigma = 5 filter.perceptual = false filter.thresholdLow = 0.02 filter.thresholdHigh = 0.05 filter.hysteresisPasses = 1 return filter.outputImage! } ```  --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)