objective-c: cv::Mat 到 CVPixelBuffer

Question

下面的代码将 cv::Mat 转换为 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

原图

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

有趣的是，Mat和CVPixelBufferRef的图片大小是一样的。

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

    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...

我非常想知道是什么导致了这种行为，我确信我遗漏了什么...

Answer 1

我在阅读 this 后找到了解决这个问题的方法。

系统喜欢图像每行 64 字节的倍数，大概是为了更好的性能，因为缓存行对齐。由于图像分辨率为 [1000 × 1000]，而不是 64 的倍数，因此每行字节数默认为 27840 不知道为什么......这导致了问题。

无论如何，如果有人正在寻找解决方案

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;
}

objective-c: cv::Mat 到 CVPixelBuffer

objective-c: cv::Mat to CVPixelBuffer

opencv

objective-c

ios