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130 lines
5.5 KiB
ReStructuredText
130 lines
5.5 KiB
ReStructuredText
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.. _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 done on *Mat*. iOS uses UIImage object to display image. One of the thing is to convert UIImage object to Mat object. Below is the code to convert UIImage to Mat.
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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
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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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CGColorSpaceRelease(colorSpace);
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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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CGColorSpaceRelease(colorSpace);
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return cvMat;
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}
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Once we obtain the Mat Object. We can do all our processing on Mat object, similar to cpp. For example if we want to convert image to gray, we can do it via below code.
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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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