OpenCV iOS - 不支持的参数组合答案

【问题标题】：OpenCV iOS - Unsupported Parameter CombinationOpenCV iOS - 不支持的参数组合
【发布时间】：2015-11-09 20:58:56
【问题描述】：

我正在使用 OpenCV 来测试图像操作。但是使用以下方法会导致错误，我无法向自己解释。

- (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，我会在 xcode 控制台中得到以下输出

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，它工作正常。

- (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;
}

我希望有人能解释一下为什么灰色方法不起作用。

【问题讨论】：

标签： c++ ios objective-c xcode opencv

【解决方案1】：

//矩阵转换

+ (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;
}

//灰度转换

+ (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"];

【讨论】：

当 OP 要求解释时，我投了反对票，但您只提供了可能正确的代码，这对理解问题没有帮助。

【解决方案2】：

- (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;
}

【讨论】：