doc/tutorials/ios/image_manipulation/image_manipulation.markdown

   1 OpenCV iOS - Image Processing {#tutorial_image_manipulation}
   2 =============================
   3
   4 @prev_tutorial{tutorial_hello}
   5 @next_tutorial{tutorial_video_processing}
   6
   7 Goal
   8 ----
   9
  10 In this tutorial we will learn how to do basic image processing using OpenCV in iOS.
  11
  12 Introduction
  13 ------------
  14
  15 In *OpenCV* all the image processing operations are usually carried out on the *Mat* structure. In
  16 iOS however, to render an image on screen it have to be an instance of the *UIImage* class. To
  17 convert an *OpenCV Mat* to an *UIImage* we use the *Core Graphics* framework available in iOS. Below
  18 is the code needed to covert back and forth between Mat's and UIImage's.
  19 @code{.m}
  20 - (cv::Mat)cvMatFromUIImage:(UIImage *)image
  21 {
  22   CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
  23   CGFloat cols = image.size.width;
  24   CGFloat rows = image.size.height;
  25
  26   cv::Mat cvMat(rows, cols, CV_8UC4); // 8 bits per component, 4 channels (color channels + alpha)
  27
  28   CGContextRef contextRef = CGBitmapContextCreate(cvMat.data,                 // Pointer to  data
  29                                                  cols,                       // Width of bitmap
  30                                                  rows,                       // Height of bitmap
  31                                                  8,                          // Bits per component
  32                                                  cvMat.step[0],              // Bytes per row
  33                                                  colorSpace,                 // Colorspace
  34                                                  kCGImageAlphaNoneSkipLast |
  35                                                  kCGBitmapByteOrderDefault); // Bitmap info flags
  36
  37   CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage);
  38   CGContextRelease(contextRef);
  39
  40   return cvMat;
  41 }
  42 @endcode
  43 @code{.m}
  44 - (cv::Mat)cvMatGrayFromUIImage:(UIImage *)image
  45 {
  46   CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
  47   CGFloat cols = image.size.width;
  48   CGFloat rows = image.size.height;
  49
  50   cv::Mat cvMat(rows, cols, CV_8UC1); // 8 bits per component, 1 channels
  51
  52   CGContextRef contextRef = CGBitmapContextCreate(cvMat.data,                 // Pointer to data
  53                                                  cols,                       // Width of bitmap
  54                                                  rows,                       // Height of bitmap
  55                                                  8,                          // Bits per component
  56                                                  cvMat.step[0],              // Bytes per row
  57                                                  colorSpace,                 // Colorspace
  58                                                  kCGImageAlphaNoneSkipLast |
  59                                                  kCGBitmapByteOrderDefault); // Bitmap info flags
  60
  61   CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage);
  62   CGContextRelease(contextRef);
  63
  64   return cvMat;
  65  }
  66 @endcode
  67 After the processing we need to convert it back to UIImage. The code below can handle both
  68 gray-scale and color image conversions (determined by the number of channels in the *if* statement).
  69 @code{.m}
  70 cv::Mat greyMat;
  71 cv::cvtColor(inputMat, greyMat, COLOR_BGR2GRAY);
  72 @endcode
  73 After the processing we need to convert it back to UIImage.
  74 @code{.m}
  75 -(UIImage *)UIImageFromCVMat:(cv::Mat)cvMat
  76 {
  77   NSData *data = [NSData dataWithBytes:cvMat.data length:cvMat.elemSize()*cvMat.total()];
  78   CGColorSpaceRef colorSpace;
  79
  80   if (cvMat.elemSize() == 1) {
  81       colorSpace = CGColorSpaceCreateDeviceGray();
  82   } else {
  83       colorSpace = CGColorSpaceCreateDeviceRGB();
  84   }
  85
  86   CGDataProviderRef provider = CGDataProviderCreateWithCFData((__bridge CFDataRef)data);
  87
  88   // Creating CGImage from cv::Mat
  89   CGImageRef imageRef = CGImageCreate(cvMat.cols,                                 //width
  90                                      cvMat.rows,                                 //height
  91                                      8,                                          //bits per component
  92                                      8 * cvMat.elemSize(),                       //bits per pixel
  93                                      cvMat.step[0],                            //bytesPerRow
  94                                      colorSpace,                                 //colorspace
  95                                      kCGImageAlphaNone|kCGBitmapByteOrderDefault,// bitmap info
  96                                      provider,                                   //CGDataProviderRef
  97                                      NULL,                                       //decode
  98                                      false,                                      //should interpolate
  99                                      kCGRenderingIntentDefault                   //intent
 100                                      );
 101
 102
 103   // Getting UIImage from CGImage
 104   UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
 105   CGImageRelease(imageRef);
 106   CGDataProviderRelease(provider);
 107   CGColorSpaceRelease(colorSpace);
 108
 109   return finalImage;
 110  }
 111 @endcode
 112
 113 Output
 114 --------
 115
 116 ![](images/output.jpg)
 117
 118 Check out an instance of running code with more Image Effects on
 119 [YouTube](http://www.youtube.com/watch?v=Ko3K_xdhJ1I) .
 120
 121 @youtube{Ko3K_xdhJ1I}