How do I find a rectangle in a photo using iphone?

Question

I will need to identify, rotate and crop a rectangle(business card) from a photo took from an iphone. I believe this can be done by using OpenCV, but I have not used it before. Could anyone give some tips on this?

Answer 1

From iOS 8, you can now use the new detector CIDetectorTypeRectangle that returns CIRectangleFeature. You can add options :

• Accuracy : low/hight

• Aspect ratio : 1.0 if you want to find only squares for example

  CIImage *image = // your image
  NSDictionary *options = @{CIDetectorAccuracy: CIDetectorAccuracyHigh, CIDetectorAspectRatio: @(1.0)};
  CIDetector *rectangleDetector = [CIDetector detectorOfType:CIDetectorTypeRectangle context:nil options:options];
  
  NSArray *rectangleFeatures = [rectangleDetector featuresInImage:image];
  
  for (CIRectangleFeature *rectangleFeature in rectangleFeatures) {
      CGPoint topLeft = rectangleFeature.topLeft;
      CGPoint topRight = rectangleFeature.topRight;
      CGPoint bottomLeft = rectangleFeature.bottomLeft;
      CGPoint bottomRight = rectangleFeature.bottomRight;
  }
  

More information in WWDC 2014 Advances in Core Image, Session 514.

An example from shinobicontrols.com