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

119 lines
5.1 KiB
Markdown
Raw Normal View History

2014-11-27 20:39:05 +08:00
OpenCV iOS - Image Processing {#tutorial_image_manipulation}
=============================
Goal
----
In this tutorial we will learn how to do basic image processing using OpenCV in iOS.
2014-11-28 21:21:28 +08:00
Introduction
------------
2014-11-27 20:39:05 +08:00
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.
2014-11-28 21:21:28 +08:00
@code{.m}
2014-11-27 20:39:05 +08:00
- (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
2014-11-28 21:21:28 +08:00
@code{.m}
2014-11-27 20:39:05 +08:00
- (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).
2014-11-28 21:21:28 +08:00
@code{.m}
2014-11-27 20:39:05 +08:00
cv::Mat greyMat;
cv::cvtColor(inputMat, greyMat, COLOR_BGR2GRAY);
@endcode
After the processing we need to convert it back to UIImage.
2014-11-28 21:21:28 +08:00
@code{.m}
2014-11-27 20:39:05 +08:00
-(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
2014-11-28 21:21:28 +08:00
Output
2014-11-27 20:39:05 +08:00
--------
2014-11-28 21:21:28 +08:00
![](images/output.jpg)
2014-11-27 20:39:05 +08:00
Check out an instance of running code with more Image Effects on
[YouTube](http://www.youtube.com/watch?v=Ko3K_xdhJ1I) .
2017-10-17 18:40:16 +08:00
@youtube{Ko3K_xdhJ1I}