c++ - ios OpenCV 增加图像尺寸

Question

下面是将 UIImage 转换为 cv::Mat

的代码

+ (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;
}

cv::Mat 的这段代码到 UIImage

+ (UIImage *)UIImageFromCVMat:(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
                                    kCGImageAlphaNone | kCGBitmapByteOrderDefault,  // Bitmap info flags
                                    provider,                                       // CGDataProviderRef
                                    NULL,                                           // Decode
                                    false,                                          // Should interpolate
                                    kCGRenderingIntentDefault);                     // Intent

    UIImage *image = [[UIImage alloc] initWithCGImage:imageRef];
    CGImageRelease(imageRef);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpace);    
    return image;
}

我将 1080*1920 (1.5 mb) 的图像转换为 cv::Mat 经过一些预处理后，我将其转换为 UIImage，它给出了大小为 2517 * 的图像1527(6 兆字节)

我不想在图像处理后增加图像尺寸。请指导我哪里做错了

//裁剪 Action

 cv::Mat undistorted = cv::Mat( cvSize(maxWidth,maxHeight), CV_8UC4);
cv::Mat original = [MMOpenCVHelper cvMatFromUIImage:_adjustedImage];


cv::warpPerspective(original, undistorted, cv::getPerspectiveTransform(src, dst), cvSize(maxWidth, maxHeight));

Answer 1

您的代码没有调整图像大小。这一定是预处理的意外副作用，您在这里没有详细说明。

 UIImage* image = self.testImage;
 NSLog(@"original UIImage: %.0f %.0f", image.size.width,image.size.height);

 cv::Mat matImage = [self cvMatFromUIImage:image];
 NSLog(@"cv matImage: %d %d", matImage.cols,matImage.rows);

 UIImage* newImage = [self UIImageFromCVMat:matImage];
 NSLog(@"new UIImage: %.0f %.0f", newImage.size.width,newImage.size.height);

original UIImage: 720 960
     cv matImage: 720 960
     new UIImage: 720 960

编辑
按照您的扩展问题，看起来好像 warpPerspective 的输出大小为 cvSize(maxWidth,maxHeight) - 这就是您将获得的大小。如果您想以输入大小结束，可以在转换回 UIImage 之前使用 resize()。或者简单地将输出 mat 设置为与输入相同的大小。