Objective-c: cv::Mat 到 CVPixelBuffer [英] objective-c: cv::Mat to CVPixelBuffer

问题描述

下面的代码将 cv::Mat 转换为 CVPixelBufferRef

Below code converts cv::Mat to CVPixelBufferRef

CVPixelBufferRef getImageBufferFromMat(cv::Mat matimg) {
    cv::cvtColor(matimg, matimg, CV_BGR2BGRA);
    
    NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                                [NSNumber numberWithBool: YES], kCVPixelBufferMetalCompatibilityKey,
                                [NSNumber numberWithBool: YES], kCVPixelBufferCGImageCompatibilityKey,
                                [NSNumber numberWithBool: YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
                                [NSNumber numberWithInt: matimg.cols], kCVPixelBufferWidthKey,
                                [NSNumber numberWithInt: matimg.rows], kCVPixelBufferHeightKey,
                                [NSNumber numberWithInt: matimg.step[0]], kCVPixelBufferBytesPerRowAlignmentKey,
                                nil];
    CVPixelBufferRef imageBuffer;

    CVReturn status = CVPixelBufferCreate(kCFAllocatorMalloc, matimg.cols, matimg.rows, kCVPixelFormatType_32BGRA, (CFDictionaryRef) CFBridgingRetain(options), &imageBuffer) ;

    CVPixelBufferLockBaseAddress(imageBuffer, 0);
    void *base = CVPixelBufferGetBaseAddress(imageBuffer);

    memcpy(base, matimg.data, matimg.total() * matimg.elemSize());
    CVPixelBufferUnlockBaseAddress(imageBuffer, 0);

    return imageBuffer;
}

问题是我得到了一半的图像

The problem is I am getting half the image

原始图片

转换后(我将 CVPixelBufferRef 转换回 UIImage 并使用 UIImageWriteToSavedPhotosAlbum 存储它只是为了检查)

After Convertion (i convert CVPixelBufferRef back to UIImage and store it using UIImageWriteToSavedPhotosAlbum just for checking)

有趣的是，Mat 和 CVPixelBufferRef 的图片大小是一样的.

Interestingly, the image size of Mat and CVPixelBufferRef are the same.

现在，我所做的是在 memcopy 之前调整图像大小，其中高度增加了 2 倍

Now, what I did was resizing the image just before memcopy, where the height is increased by 2 folds

    CVPixelBufferLockBaseAddress(imageBuffer, 0);
    void *base = CVPixelBufferGetBaseAddress(imageBuffer);

    cv::resize(matimg, matimg, cv::Size(), 1 , 2);
    memcpy(base, matimg.data, matimg.total() * matimg.elemSize());
    CVPixelBufferUnlockBaseAddress(imageBuffer, 0);

现在图片大小还是一样...

Now the image size is still the same...

我非常想知道是什么导致了这种行为，而且我确定我遗漏了一些东西......

I want to badly know what's causing this behavior and I am sure I am missing something...

推荐答案

我在阅读这篇.

系统喜欢图像为每行 64 字节的倍数，大概是为了由于缓存行对齐而获得更好的性能.由于图像分辨率是 [1000 × 1000]，不是 64 的倍数，因此每行的字节数默认为 27840 不知道为什么......这导致了问题.

The system likes images to be a multiple of 64 bytes per row, presumably for better performance due to cache line alignment. As image resolution is [1000 × 1000], not multiple of 64 hence bytes per row would default to 27840 don't know why... This was causing the problems.

无论如何，如果有人在寻找解决方案

Anyway, if anyone looking for the solution

CVPixelBufferRef getImageBufferFromMat(cv::Mat matimg) {
    cv::cvtColor(matimg, matimg, CV_BGR2BGRA);
    
    int widthReminder = matimg.cols % 64, heightReminder = matimg.rows % 64;
    if (widthReminder != 0 || heightReminder != 0) {
        cv::resize(matimg, matimg, cv::Size(matimg.cols + (64 - widthReminder), matimg.rows + (64 - heightReminder)));
    }

    NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                                [NSNumber numberWithBool: YES], kCVPixelBufferMetalCompatibilityKey,
                                [NSNumber numberWithBool: YES], kCVPixelBufferCGImageCompatibilityKey,
                                [NSNumber numberWithBool: YES], kCVPixelBufferCGBitmapContextCompatibilityKey,
                                [NSNumber numberWithInt: matimg.cols], kCVPixelBufferWidthKey,
                                [NSNumber numberWithInt: matimg.rows], kCVPixelBufferHeightKey,
                                [NSNumber numberWithInt: matimg.step[0]], kCVPixelBufferBytesPerRowAlignmentKey,
                                nil];
    CVPixelBufferRef imageBuffer;
    CVReturn status = CVPixelBufferCreate(kCFAllocatorMalloc, matimg.cols, matimg.rows, kCVPixelFormatType_32BGRA, (CFDictionaryRef) CFBridgingRetain(options), &imageBuffer) ;
    NSParameterAssert(status == kCVReturnSuccess && imageBuffer != NULL);
    
    CVPixelBufferLockBaseAddress(imageBuffer, 0);
    void *base = CVPixelBufferGetBaseAddress(imageBuffer);
    memcpy(base, matimg.data, matimg.total() * matimg.elemSize());
    CVPixelBufferUnlockBaseAddress(imageBuffer, 0);

//    UIImageWriteToSavedPhotosAlbum(converts(imageBuffer), nil, nil, nil);
    return imageBuffer;
} 

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