我正在开发一个使用某些 opencv 功能(删除背景、边缘检测等)的 ios 应用程序

除其他外，我加载透明图像 (png)。由于某些原因，当我加载图像时，opencv 决定忽略一些透明区域，同时尊重其他区域。我可以通过将我的半透明 UIImage 转换为 IplImage 然后再转换回 UIImage(不对 iplimage 执行任何操作)并将两个图像保存到本地文件来看到这一点。

这是我用于将 UIImage 转换为 IplImage 以及向后转换的代码:

- (IplImage *)CreateIplImageFromUIImageWithTransparency:(UIImage *)image {
    // Getting CGImage from UIImage
    CGImageRef imageRef = image.CGImage;

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    // Creating temporal IplImage for drawing
    IplImage *iplimage = cvCreateImage(
                                       cvSize(image.size.width,image.size.height), IPL_DEPTH_8U, 4
                                       );
    // Creating CGContext for temporal IplImage
    CGContextRef contextRef = CGBitmapContextCreate(
                                                    iplimage->imageData, iplimage->width, iplimage->height,
                                                    iplimage->depth, iplimage->widthStep,
                                                    colorSpace, kCGImageAlphaPremultipliedLast|kCGBitmapByteOrderDefault
                                                    );
    // Drawing CGImage to CGContext
    CGContextDrawImage(
                       contextRef,
                       CGRectMake(0, 0, image.size.width, image.size.height),
                       imageRef
                       );
    CGContextRelease(contextRef);
    CGColorSpaceRelease(colorSpace);

    // Creating result IplImage
    IplImage *ret = cvCreateImage(cvGetSize(iplimage), IPL_DEPTH_8U, 4);
    cvCvtColor(iplimage, ret, CV_RGBA2BGRA);
    cvReleaseImage(&iplimage);

    return ret;
}


- (UIImage *)UIImageFromIplImage:(IplImage *)image {
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    NSData *data = [NSData dataWithBytes:image->imageData length:image->imageSize];
    CGDataProviderRef provider = CGDataProviderCreateWithCFData((__bridge CFDataRef)data);
    CGImageRef imageRef = CGImageCreate(image->width, image->height,
                                        image->depth, image->depth * image->nChannels, image->widthStep,
                                        colorSpace, kCGBitmapByteOrderDefault | kCGImageAlphaLast ,
                                        provider, NULL, false, kCGRenderingIntentDefault);
    UIImage *ret = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpace);
    return ret;
}

可能导致此行为的原因是什么？

谢谢

最佳答案

这段代码对我有用。我修改了 here 中的代码

从 UIImage 读取

-(cv::Mat)CVMat
{

    CGColorSpaceRef colorSpace = CGImageGetColorSpace(self.CGImage);
    CGFloat cols = self.size.width;
    CGFloat rows = self.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 |
                                                    kCGImageAlphaPremultipliedLast |
                                                    kCGBitmapByteOrderDefault); // Bitmap info flags

    CGContextDrawImage(contextRef, CGRectMake(0, 0, cols, rows), self.CGImage);
    CGContextRelease(contextRef);

    return cvMat;
}

转换回 UIImage:

+ (UIImage *)imageWithCVMat:(const cv::Mat&)cvMat
{
    return [[UIImage alloc] initWithCVMat:cvMat];
}

- (id)initWithCVMat:(const 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);

    CGImageRef imageRef = CGImageCreate(cvMat.cols,                                     // Width
                                        cvMat.rows,                                     // Height
                                        8,                                              // Bits per component
                                        8 * cvMat.elemSize(),                           // Bits per pixel
                                        cvMat.step[0],                                  // Bytes per row
                                        colorSpace,                                     // Colorspace
                                        kCGImageAlphaPremultipliedLast | kCGBitmapByteOrderDefault,  // Bitmap info flags
                                        provider,                                       // CGDataProviderRef
                                        NULL,                                           // Decode
                                        false,                                          // Should interpolate
                                        kCGRenderingIntentDefault);                     // Intent   

    self = [self initWithCGImage:imageRef];
    CGImageRelease(imageRef);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpace);

    return self;
}

关于ios - opencv ios透明图像加载没有透明度，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/16965632/