Note: most implementations don't correctly handle an alpha channel or convert from OpenCV's BGR pixel format to iOS's RGB.
This will correctly convert from cv::Mat
to UIImage
:
+(UIImage *)UIImageFromCVMat:(cv::Mat)cvMat {
NSData *data = [NSData dataWithBytes:cvMat.data length:image.step.p[0]*image.rows];
CGColorSpaceRef colorSpace;
CGBitmapInfo bitmapInfo;
if (cvMat.elemSize() == 1) {
colorSpace = CGColorSpaceCreateDeviceGray();
bitmapInfo = kCGImageAlphaNone | kCGBitmapByteOrderDefault;
} else {
colorSpace = CGColorSpaceCreateDeviceRGB();
bitmapInfo = kCGBitmapByteOrder32Little | (
cvMat.elemSize() == 3? kCGImageAlphaNone : kCGImageAlphaNoneSkipFirst
);
}
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
bitmapInfo, // 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;
}
And to convert from UIImage
to cv::Mat
:
+ (cv::Mat)cvMatWithImage:(UIImage *)image
{
CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
size_t numberOfComponents = CGColorSpaceGetNumberOfComponents(colorSpace);
CGFloat cols = image.size.width;
CGFloat rows = image.size.height;
cv::Mat cvMat(rows, cols, CV_8UC4); // 8 bits per component, 4 channels
CGBitmapInfo bitmapInfo = kCGImageAlphaNoneSkipLast | kCGBitmapByteOrderDefault;
// check whether the UIImage is greyscale already
if (numberOfComponents == 1){
cvMat = cv::Mat(rows, cols, CV_8UC1); // 8 bits per component, 1 channels
bitmapInfo = kCGImageAlphaNone | kCGBitmapByteOrderDefault;
}
CGContextRef contextRef = CGBitmapContextCreate(cvMat.data, // Pointer to backing data
cols, // Width of bitmap
rows, // Height of bitmap
8, // Bits per component
cvMat.step[0], // Bytes per row
colorSpace, // Colorspace
bitmapInfo); // Bitmap info flags
CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage);
CGContextRelease(contextRef);
return cvMat;
}
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