OpenCV/opencv/doc/tutorials/ios/image_manipulation/image_manipulation.markdown

OpenCV iOS - Image Processing {#tutorial_image_manipulation}

@tableofcontents

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| | | | -: | :- | | Original author | Charu Hans | | Compatibility | OpenCV >= 3.0 |

Goal

In this tutorial we will learn how to do basic image processing using OpenCV in iOS.

Introduction

In OpenCV all the image processing operations are usually carried out on the Mat structure. In iOS however, to render an image on screen it have to be an instance of the UIImage class. To convert an OpenCV Mat to an UIImage we use the Core Graphics framework available in iOS. Below is the code needed to covert back and forth between Mat's and UIImage's. @code{.m}

• (cv::Mat)cvMatFromUIImage:(UIImage *)image { CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage); CGFloat cols = image.size.width; CGFloat rows = image.size.height;

cv::Mat cvMat(rows, cols, CV_8UC4); // 8 bits per component, 4 channels (color channels + alpha)

CGContextRef contextRef = CGBitmapContextCreate(cvMat.data, // Pointer to data

                                             cols,                       // Width of bitmap
                                             rows,                       // Height of bitmap
                                             8,                          // Bits per component
                                             cvMat.step[0],              // Bytes per row
                                             colorSpace,                 // Colorspace
                                             kCGImageAlphaNoneSkipLast |
                                             kCGBitmapByteOrderDefault); // Bitmap info flags

CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage); CGContextRelease(contextRef);

return cvMat; } @endcode @code{.m}

• (cv::Mat)cvMatGrayFromUIImage:(UIImage *)image { CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage); CGFloat cols = image.size.width; CGFloat rows = image.size.height;

cv::Mat cvMat(rows, cols, CV_8UC1); // 8 bits per component, 1 channels

CGContextRef contextRef = CGBitmapContextCreate(cvMat.data, // Pointer to data

                                             cols,                       // Width of bitmap
                                             rows,                       // Height of bitmap
                                             8,                          // Bits per component
                                             cvMat.step[0],              // Bytes per row
                                             colorSpace,                 // Colorspace
                                             kCGImageAlphaNoneSkipLast |
                                             kCGBitmapByteOrderDefault); // Bitmap info flags

CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage); CGContextRelease(contextRef);

return cvMat; } @endcode After the processing we need to convert it back to UIImage. The code below can handle both gray-scale and color image conversions (determined by the number of channels in the if statement). @code{.m} cv::Mat greyMat; cv::cvtColor(inputMat, greyMat, COLOR_BGR2GRAY); @endcode After the processing we need to convert it back to UIImage. @code{.m} -(UIImage *)UIImageFromCVMat:(cv::Mat)cvMat { NSData *data = [NSData dataWithBytes:cvMat.data length:cvMat.elemSize()*cvMat.total()]; CGColorSpaceRef colorSpace;

if (cvMat.elemSize() == 1) {

  colorSpace = CGColorSpaceCreateDeviceGray();

} else {

  colorSpace = CGColorSpaceCreateDeviceRGB();

}

CGDataProviderRef provider = CGDataProviderCreateWithCFData((__bridge CFDataRef)data);

// Creating CGImage from cv::Mat CGImageRef imageRef = CGImageCreate(cvMat.cols, //width

                                 cvMat.rows,                                 //height
                                 8,                                          //bits per component
                                 8 * cvMat.elemSize(),                       //bits per pixel
                                 cvMat.step[0],                            //bytesPerRow
                                 colorSpace,                                 //colorspace
                                 kCGImageAlphaNone|kCGBitmapByteOrderDefault,// bitmap info
                                 provider,                                   //CGDataProviderRef
                                 NULL,                                       //decode
                                 false,                                      //should interpolate
                                 kCGRenderingIntentDefault                   //intent
                                 );

// Getting UIImage from CGImage UIImage *finalImage = [UIImage imageWithCGImage:imageRef]; CGImageRelease(imageRef); CGDataProviderRelease(provider); CGColorSpaceRelease(colorSpace);

return finalImage; } @endcode

Output

Check out an instance of running code with more Image Effects on YouTube .

@youtube{Ko3K_xdhJ1I}