Using OpenCV in Swift iOS

Question

After adding the OpenCV 2 framework in my xcode project, I tried searching for samlpes or tutorials for integration with swift.

Are there any good tutorials for the same?

Answer 1

OpenCV is a framework written in C++. Apple's reference tell us that

You cannot import C++ code directly into Swift. Instead, create an Objective-C or C wrapper for C++ code.

so you cannot directly import and use OpenCV in a swift project, but this is actually not bad at all because you (need) continue to use the C++ syntax of the framework which is pretty well documented all over the net.

So how do you proceed?

1. Create a new Objective-C++ class (.h, .mm) for calling C++ OpenCV

OpenCVWrapper.h

#import <UIKit/UIKit.h> #import <Foundation/Foundation.h>  @interface OpenCVWrapper : NSObject      + (UIImage *)processImageWithOpenCV:(UIImage*)inputImage;  @end 

OpenCVWrapper.mm (use the File -> New... Wizard for Objective-C and rename the .m file to .mm)

#include "OpenCVWrapper.h" #import "UIImage+OpenCV.h" // See below to create this  #include <opencv2/opencv.hpp>  using namespace cv; using namespace std;  @implementation OpenCVWrapper : NSObject      + (UIImage *)processImageWithOpenCV:(UIImage*)inputImage {         Mat mat = [inputImage CVMat];                  // do your processing here         ...                  return [UIImage imageWithCVMat:mat];     }  @end 

As an alternative to creating new classes such as the example OpenCVWrapper.h/mm you can use Objective-C categories to extend existing Objective-C classes with OpenCV functionality. For instance UIImage+OpenCV category:

UIImage+OpenCV.h

#import <UIKit/UIKit.h> #import <opencv2/opencv.hpp>  @interface UIImage (OpenCV)      //cv::Mat to UIImage + (UIImage *)imageWithCVMat:(const cv::Mat&)cvMat; - (id)initWithCVMat:(const cv::Mat&)cvMat;      //UIImage to cv::Mat - (cv::Mat)CVMat; - (cv::Mat)CVMat3;  // no alpha channel - (cv::Mat)CVGrayscaleMat;  @end 

UIImage+OpenCV.mm

See https://github.com/foundry/OpenCVSwiftStitch/blob/master/SwiftStitch/UIImage%2BOpenCV.mm

2. Update the Bridging-Header to make all Objective-C++ classes you created available to Swift by importing our newly created wrappers (#import "OpenCVWrapper.h")

3. Use your wrapper in your Swift files:

   let image = UIImage(named: "image.jpeg") let processedImage = OpenCVWrapper.processImageWithOpenCV(image) 

All Objective-C++ classes included in the bridge header are available directly from Swift.

Answer 2

I have a demo on github:

https://github.com/foundry/OpenCVSwiftStitch

It shows how to use the OpenCV stitcher from a Swift-based project. There is not a lot to the openCV side, it's really just a demo of how to put the various pieces together.

As Swift won't talk C++ directly, it uses a thin Objective-C++ wrapper to mediate between the iOS side and the openCV side.

Made in answer to these questions:
Can I mix Swift with C++? Like the Objective - C .mm files
libraries to CAPTURE panorama in iOS 6