Question

First, I apology for this newbie question. I’m new in Objective C and OpenCV

the normal method declaration in Objective-C is like that

Function functionName = [[Function alloc] init];

but when I use OpenCV class it says (for example CvMat) receiver type is not an Objective C class.

or am I suppose to write the code in C++ syntax ?

Answer 1

You write the code in C++ syntax. Objective-C is actually a superset of C++ which means that any C++ program is also a valid Objective-C program (well in most cases anyway). Objective-C just adds a whole lot of functionality to what already exists in C++.

When I was developing an openCV app for iOS, here were the main stumbling blocks:

• Compiling OpenCV as a static library. It’s the only way to use OpenCV in iOS, and is not an easy task if you’ve never done anything similar before. There are a couple of great blog posts about how to do it, such as this one.

• Armv6 and armv7 – make sure you have static libraries compiled for both (or a universal binary), as iOS runs on both.

• When you’re coding, just code as you would for c++. Here’s a chunk of example code you can refer to.

  // NOTE you SHOULD cvReleaseImage() for the return value when end of the code.
  - (IplImage *)CreateIplImageFromUIImage:(UIImage *)image {
    // Getting CGImage from UIImage
    CGImageRef imageRef = image.CGImage;
  
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    // Creating temporal IplImage for drawing
    IplImage *iplimage = cvCreateImage(
      cvSize(image.size.width,image.size.height), IPL_DEPTH_8U, 4
    );
    // Creating CGContext for temporal IplImage
    CGContextRef contextRef = CGBitmapContextCreate(
      iplimage->imageData, iplimage->width, iplimage->height,
      iplimage->depth, iplimage->widthStep,
      colorSpace, kCGImageAlphaPremultipliedLast|kCGBitmapByteOrderDefault
    );
    // Drawing CGImage to CGContext
    CGContextDrawImage(
      contextRef,
      CGRectMake(0, 0, image.size.width, image.size.height),
      imageRef
    );
    CGContextRelease(contextRef);
    CGColorSpaceRelease(colorSpace);
  
    // Creating result IplImage
    IplImage *ret = cvCreateImage(cvGetSize(iplimage), IPL_DEPTH_8U, 3);
    cvCvtColor(iplimage, ret, CV_RGBA2BGR);
    cvReleaseImage(&iplimage);
  
    return ret;
  }