Mat from UIImage (iOS) differences between emulator and device

asked 2013-11-14 03:18:59 -0600

Ricciolo
51 ●2

I'm using this function to convert UIImage to Mat

- (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

On emulator it works great and I get image processing as expected. When using the same code on the device with the same image (same jpeg file) I get unexpected result. Looking inside Mat I see different pixel data. Do you know why?

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Could you attach results for simulator and real device? What version of iOS do you use? What device?

AlexanderShishkov ( 2013-11-14 04:06:51 -0600 )edit

Device is iPhone 4 with iOS 7.0.3 If I dump cvMat.at<uchar>(0,0) cvMat.at<uchar>(1,0) I get on simulator: c b on iphone: c c

Ricciolo ( 2013-11-14 04:32:17 -0600 )edit

That's odd, but using imread the cv::Mat is correct. But the image will come from UIImagePickerController so I need to convert from UIImage

Ricciolo ( 2013-11-14 08:37:09 -0600 )edit

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void UIImageToMat(const UIImage* image, cv::Mat& m, bool alphaExist) { CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage); CGFloat cols = image.size.width, rows = image.size.height; CGContextRef contextRef; CGBitmapInfo bitmapInfo = kCGImageAlphaPremultipliedLast; if (CGColorSpaceGetModel(colorSpace) == 0) { m.create(rows, cols, CV_8UC1); // 8 bits per component, 1 channel bitmapInfo = kCGImageAlphaNone; if (!alphaExist) bitmapInfo = kCGImageAlphaNone; contextRef = CGBitmapContextCreate(m.data, m.cols, m.rows, 8, m.step[0], colorSpace, bitmapInfo); } else { m.create(rows, cols, CV_8UC4); // 8 bits per component, 4 channels if (!alphaExist) bitmapInfo = kCGImageAlphaNoneSkipLast | kCGBitmapByteOrderDefault; contextRef = CGBitmapContextCreate(m.data, m.cols, m.rows, 8, m.step[0], colorSpace, bitmapInfo); } CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage); CGContextRelease(contextRef); CGColorSpaceRelease(colorSpace); }

Mat from UIImage (iOS) differences between emulator and device

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Mat from UIImage (iOS) differences between emulator and device