SwiftUI + Vision Contour Request — Coin Detection in iOS

Apple boosts its computer vision ambitions with a bunch of new Vision requests


Apple’s WWDC 2020 (digital-only) event kickstarted with a bang. There were a lot of new surprises from the world of SwiftUI, ARKit, PencilKit, Create ML, and Core ML. But the one that stood out for me was computer vision.

Apple’s Vision framework got bolstered with a bunch of exciting new APIs that perform some complex and critical computer vision algorithms in a fairly straightforward way.

Starting with iOS 14, the Vision framework now supports Hand and Body Pose Estimation, Optical Flow, Trajectory Detection, and Contour Detection.

While we’ll provide an in-depth look at each of these some other time, right now, let’s dive deeper into one particularly interesting addition—the contour detection Vision request.

Our Goal

  • Understanding Vision’s contour detection request.
  • Running it in an iOS 14 SwiftUI application to detect contours along coins.
  • Simplifying the contours by leveraging Core Image filters for pre-processing the images before passing them on to the Vision request. We’ll look to mask the images in order to reduce texture noise.

Vision Contour Detection

Contour detection detects outlines of the edges in an image. Essentially, it joins all the continuous points that have the same color or intensity.

This computer vision task is useful for shape analysis, edge detection, and is helpful in scenarios where you need to find similar types of objects in an image.

Coin detection and segmentation is a fairly common use case in OpenCV, and now by using Vision’s new VNDetectContoursRequest, we can perform the same in our iOS applications easily (without the need for third-party libraries).

To process images or frames, the Vision framework requires a VNRequest, which is passed into an image request handler or a sequence request handler. What we get in return is a VNObservation class.

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