OpenCV iOS -不支持的参数组合

OpenCV iOS - Unsupported Parameter Combination

本文关键字：参数 组合 不支持 iOS OpenCV      更新时间：2023-10-16

我使用OpenCV来测试图像操作。但是使用下面的方法会导致一个错误，这是我无法解释的。

- (cv::Mat)cvMatGrayFromUIImage:(UIImage *)image
{
    CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
    CGFloat cols = image.size.width;
    CGFloat rows = image.size.height;
    cv::Mat cvMat = cv::Mat(rows, cols, CV_8UC1); // 8 bits per component, 1 channel
    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
                                                    kCGImageAlphaNone |
                                                    kCGBitmapByteOrderDefault); // Bitmap info flags
    CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage);
    CGContextRelease(contextRef);
    CGColorSpaceRelease(colorSpace);
    return cvMat;
}

当我运行这个方法时，我得到以下输出到xcode控制台

Aug 17 11:14:24  OpenCVDemo[1250] <Error>: CGBitmapContextCreate: unsupported parameter combination: set CGBITMAP_CONTEXT_LOG_ERRORS environmental variable to see the details
Aug 17 11:14:24  OpenCVDemo[1250] <Error>: CGContextDrawImage: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

例如，这里有一个方法，它工作得很好。

- (cv::Mat)cvMat3ChannelFromUIImage:(UIImage *)image
{
    CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
    CGFloat cols = image.size.width;
    CGFloat rows = image.size.height;
    cv::Mat rgba(rows, cols, CV_8UC4, cvScalar(1,2,3,4)); // 8 bits per component, 4 channels
    CGContextRef contextRef = CGBitmapContextCreate(rgba.data,                 // Pointer to backing data
                                                    cols,                      // Width of bitmap
                                                    rows,                     // Height of bitmap
                                                    8,                          // Bits per component
                                                    rgba.step[0],              // Bytes per row
                                                    colorSpace,                 // Colorspace
                                                    kCGImageAlphaNoneSkipLast |
                                                    kCGBitmapByteOrderDefault); // Bitmap info flags
    CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage);
    CGContextRelease(contextRef);
    cv::Mat bgr( rgba.rows, rgba.cols, CV_8UC3 );
    cv::Mat alpha( rgba.rows, rgba.cols, CV_8UC1 );
    cv::Mat out[] = { bgr, alpha };
    // rgba[0] -> bgr[2], rgba[1] -> bgr[1],
    // rgba[2] -> bgr[0], rgba[3] -> alpha[0]
    int from_to[] = { 0,2, 1,1, 2,0, 3,3 };
    mixChannels( &rgba, 1, out, 2, from_to, 4 );
    return bgr;
}

我希望这里有人可以解释，为什么灰色方法不工作。

- (cv::Mat)cvMat3ChannelFromUIImage:(UIImage *)image
{
    UIImage *theImage = [UIImage imageWithData:UIImagePNGRepresentation(image)];
    CGColorSpaceRef colorSpace = CGImageGetColorSpace(theImage.CGImage);
    CGFloat cols = theImage.size.width;
    CGFloat rows = theImage.size.height;
    cv::Mat rgba(rows, cols, CV_8UC4, cvScalar(1,2,3,4)); // 8 bits per component, 4 channels
    CGContextRef contextRef = CGBitmapContextCreate(rgba.data,                 // Pointer to backing data
                                                    cols,                      // Width of bitmap
                                                    rows,                     // Height of bitmap
                                                    8,                          // Bits per component
                                                    rgba.step[0],              // Bytes per row
                                                    colorSpace,                 // Colorspace
                                                    kCGImageAlphaNoneSkipLast |
                                                    kCGBitmapByteOrderDefault); // Bitmap info flags
    CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), theImage.CGImage);
    CGContextRelease(contextRef);
    cv::Mat bgr( rgba.rows, rgba.cols, CV_8UC3 );
    cv::Mat alpha( rgba.rows, rgba.cols, CV_8UC1 );
    cv::Mat out[] = { bgr, alpha };
    // rgba[0] -> bgr[2], rgba[1] -> bgr[1],
    // rgba[2] -> bgr[0], rgba[3] -> alpha[0]
    int from_to[] = { 0,2, 1,1, 2,0, 3,3 };
    mixChannels( &rgba, 1, out, 2, from_to, 4 );
    return bgr;
}

//Mat转换

+ (cv::Mat)cvMatFromUIImage:(UIImage *)image
{
CGColorSpaceRef colorSpace = CGImageGetColorSpace(image.CGImage);
CGFloat cols,rows;
if  (image.imageOrientation == UIImageOrientationLeft
     || image.imageOrientation == UIImageOrientationRight) {
    cols = image.size.height;
    rows = image.size.width;
}
else{
    cols = image.size.width;
    rows = image.size.height;
}

cv::Mat cvMat(rows, cols, CV_8UC4); // 8 bits per component, 4 channels
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
                                                kCGImageAlphaNoneSkipLast |
                                                kCGBitmapByteOrderDefault);
CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), image.CGImage);
CGContextRelease(contextRef);

cv::Mat cvMatTest;
cv::transpose(cvMat, cvMatTest);
if  (image.imageOrientation == UIImageOrientationLeft
     || image.imageOrientation == UIImageOrientationRight) {
}
else{
    return cvMat;
}
cvMat.release();
cv::flip(cvMatTest, cvMatTest, 1);

return cvMatTest;
}

//灰色转换
+ (cv::Mat)cvMatGrayFromUIImage:(UIImage *)image
{
cv::Mat cvMat = [self cvMatFromUIImage:image];
cv::Mat grayMat;
if ( cvMat.channels() == 1 ) {
    grayMat = cvMat;
}
else {
    grayMat = cv :: Mat( cvMat.rows,cvMat.cols, CV_8UC1 );
    cv::cvtColor( cvMat, grayMat, CV_BGR2GRAY );
}
return grayMat;
}

//调用上述方法

cv::Mat grayImage = [self cvMatGrayFromUIImage:"your image"];

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