130 lines
5.5 KiB
ReStructuredText
130 lines
5.5 KiB
ReStructuredText
.. _OpenCViOSImageManipulation:
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OpenCV iOS - Image Processing
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*******************************
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Goal
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====
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In this tutorial we will learn how to do basic image processing using OpenCV in iOS.
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*Introduction*
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==============
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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.
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.. code-block:: cpp
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- (cv::Mat)cvMatFromUIImage:(UIImage *)image
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{
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CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
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CGFloat cols = image.size.width;
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CGFloat rows = image.size.height;
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cv::Mat cvMat(rows, cols, CV_8UC4); // 8 bits per component, 4 channels (color channels + alpha)
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CGContextRef contextRef = CGBitmapContextCreate(cvMat.data, // Pointer to data
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cols, // Width of bitmap
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rows, // Height of bitmap
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8, // Bits per component
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cvMat.step[0], // Bytes per row
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colorSpace, // Colorspace
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kCGImageAlphaNoneSkipLast |
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kCGBitmapByteOrderDefault); // Bitmap info flags
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CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage);
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CGContextRelease(contextRef);
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return cvMat;
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}
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.. code-block:: cpp
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- (cv::Mat)cvMatGrayFromUIImage:(UIImage *)image
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{
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CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
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CGFloat cols = image.size.width;
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CGFloat rows = image.size.height;
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cv::Mat cvMat(rows, cols, CV_8UC1); // 8 bits per component, 1 channels
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CGContextRef contextRef = CGBitmapContextCreate(cvMat.data, // Pointer to data
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cols, // Width of bitmap
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rows, // Height of bitmap
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8, // Bits per component
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cvMat.step[0], // Bytes per row
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colorSpace, // Colorspace
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kCGImageAlphaNoneSkipLast |
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kCGBitmapByteOrderDefault); // Bitmap info flags
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CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage);
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CGContextRelease(contextRef);
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return cvMat;
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}
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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).
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.. code-block:: cpp
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cv::Mat greyMat;
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cv::cvtColor(inputMat, greyMat, CV_BGR2GRAY);
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After the processing we need to convert it back to UIImage.
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.. code-block:: cpp
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-(UIImage *)UIImageFromCVMat:(cv::Mat)cvMat
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{
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NSData *data = [NSData dataWithBytes:cvMat.data length:cvMat.elemSize()*cvMat.total()];
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CGColorSpaceRef colorSpace;
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if (cvMat.elemSize() == 1) {
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colorSpace = CGColorSpaceCreateDeviceGray();
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} else {
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colorSpace = CGColorSpaceCreateDeviceRGB();
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}
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CGDataProviderRef provider = CGDataProviderCreateWithCFData((__bridge CFDataRef)data);
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// Creating CGImage from cv::Mat
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CGImageRef imageRef = CGImageCreate(cvMat.cols, //width
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cvMat.rows, //height
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8, //bits per component
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8 * cvMat.elemSize(), //bits per pixel
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cvMat.step[0], //bytesPerRow
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colorSpace, //colorspace
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kCGImageAlphaNone|kCGBitmapByteOrderDefault,// bitmap info
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provider, //CGDataProviderRef
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NULL, //decode
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false, //should interpolate
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kCGRenderingIntentDefault //intent
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);
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// Getting UIImage from CGImage
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UIImage *finalImage = [UIImage imageWithCGImage:imageRef];
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CGImageRelease(imageRef);
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CGDataProviderRelease(provider);
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CGColorSpaceRelease(colorSpace);
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return finalImage;
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}
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*Output*
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==================================
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.. image:: images/output.jpg
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:alt: header
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:align: center
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Check out an instance of running code with more Image Effects on `YouTube <http://www.youtube.com/watch?v=Ko3K_xdhJ1I>`_ .
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.. raw:: html
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<div align="center">
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<iframe width="560" height="350" src="http://www.youtube.com/embed/Ko3K_xdhJ1I" frameborder="0" allowfullscreen></iframe>
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</div>
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