Quadrilateral recognition on iOS devices using the OpenCV C++ Library. Uses perspective warping to map an image to the detected shape. Main code found in /Recognizr/SquareDetector.mm should you want to adapt/use it for your project.

• Resize CvVideoCameraDelegate output image to quarter size using pyrDown
• Blur, dilate and then erode to average and remove noise
• Filter to binary black/white (CV_THRESH_BINARY), compute threshold using Otsu algorithm (CV_THRESH_OTSU)
• Use Canny edge detector to output edges only
• Find contours
• Construct quads from contours using minimum angle threshold

First make sure you have CocoaPods installed then add OpenCV to your Podfile:

target ‘MyApp’ do
  pod 'OpenCV', '~> 2.4'
end

Then simply run the following to install:

pod install

Dog image from Unsplash: https://unsplash.com/photos/pgUbpDLJh3E