将CMSampleBufferRef转换为UIImage [英] convert CMSampleBufferRef to UIImage

问题描述

我用AVCaptureSession捕捉视频。
但我想将捕获的图像转换为UIImage。

I'm captuting video with AVCaptureSession. But I would like to convert the captured image to an UIImage.

我在互联网上找到了一些代码：

I found some code on Internet:

- (UIImage *) imageFromSampleBuffer:(CMSampleBufferRef) sampleBuffer
{

    NSLog(@"imageFromSampleBuffer: called");
    // Get a CMSampleBuffer's Core Video image buffer for the media data
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    // Lock the base address of the pixel buffer
    CVPixelBufferLockBaseAddress(imageBuffer, 0);

    // Get the number of bytes per row for the pixel buffer
    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);

    // Get the number of bytes per row for the pixel buffer
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
    // Get the pixel buffer width and height
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);

    // Create a device-dependent RGB color space
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    // Create a bitmap graphics context with the sample buffer data
    CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8,
                                                 bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    // Create a Quartz image from the pixel data in the bitmap graphics context
    CGImageRef quartzImage = CGBitmapContextCreateImage(context);
    // Unlock the pixel buffer
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);


    // Free up the context and color space
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);

    // Create an image object from the Quartz image
    UIImage *image = [UIImage imageWithCGImage:quartzImage];

    // Release the Quartz image
    CGImageRelease(quartzImage);

    return (image);
}

但我收到了一些错误：

Jan 17 17:39:25 iPhone-4-de-XXX ThinkOutsideTheBox[2363] <Error>: CGBitmapContextCreate: invalid data bytes/row: should be at least 2560 for 8 integer bits/component, 3 components, kCGImageAlphaPremultipliedFirst.
Jan 17 17:39:25 iPhone-4-de-XXX ThinkOutsideTheBox[2363] <Error>: CGBitmapContextCreateImage: invalid context 0x0
2013-01-17 17:39:25.896 ThinkOutsideTheBox[2363:907] image <UIImage: 0x1d553f00>
Jan 17 17:39:25 iPhone-4-de-XXX ThinkOutsideTheBox[2363] <Error>: CGContextDrawImage: invalid context 0x0
Jan 17 17:39:25 iPhone-4-de-XXX ThinkOutsideTheBox[2363] <Error>: CGBitmapContextGetData: invalid context 0x0

编辑：
我也使用UIImage来获得rgb颜色：

I also use the UIImage to get the rgb color:

-(void) captureOutput:(AVCaptureOutput*)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection*)connection
{

    UIImage* image = [self imageFromSampleBuffer:sampleBuffer];
    unsigned char* pixels = [image rgbaPixels];
    double totalLuminance = 0.0;
    for(int p=0;p<image.size.width*image.size.height*4;p+=4)
    {
        totalLuminance += pixels[p]*0.299 + pixels[p+1]*0.587 + pixels[p+2]*0.114;
    }
    totalLuminance /= (image.size.width*image.size.height);
    totalLuminance /= 255.0;
    NSLog(@"totalLuminance %f",totalLuminance);

}

推荐答案

你最好的下注将是将捕获视频数据输出的 videoSettings 设置为指定您想要的像素格式，您需要设置它CGBitmapContext可以处理RGB的一些变化。

Your best bet will be to set the capture video data output's videoSettings to a dictionary that specifies the pixel format you want, which you'll need to set to some variation on RGB that CGBitmapContext can handle.

该文档有所有像素列表核心视频可以处理的rmats 。 CGBitmapContext仅支持其中的一小部分。您在互联网上找到的代码所期望的格式是 kCVPixelFormatType_32BGRA ，但这可能是针对Macs-on iOS设备编写的， kCVPixelFormatType_32ARGB （big-endian）可能会更快。尝试使用在设备上，并比较帧速率。

The documentation has a list of all of the pixel formats that Core Video can process. Only a tiny subset of those are supported by CGBitmapContext. The format that the code you found on the internet is expecting is kCVPixelFormatType_32BGRA, but that might have been written for Macs—on iOS devices, kCVPixelFormatType_32ARGB (big-endian) might be faster. Try them both, on the device, and compare frame rates.

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