如何将CVImageBufferRef转换为UIImage [英] how to convert a CVImageBufferRef to UIImage

问题描述

我正在尝试从相机捕捉视频。我已经得到 captureOutput：didOutputSampleBuffer：回调触发它，它给了我一个样本缓冲区，然后我转换为 CVImageBufferRef 。然后我尝试将该图像转换为 UIImage 然后我可以在我的应用中查看。

I am trying to capture video from a camera. i have gotten the captureOutput:didOutputSampleBuffer: callback to trigger and it gives me a sample buffer that i then convert to a CVImageBufferRef. i then attempt to convert that image to a UIImage that i can then view in my app.

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection
{
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer); 
    /*Lock the image buffer*/
    CVPixelBufferLockBaseAddress(imageBuffer,0); 
    /*Get information about the image*/
    uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(imageBuffer); 
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer); 
    size_t width = CVPixelBufferGetWidth(imageBuffer); 
    size_t height = CVPixelBufferGetHeight(imageBuffer); 

    /*We unlock the  image buffer*/
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);

    /*Create a CGImageRef from the CVImageBufferRef*/
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB(); 
    CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst); 
    CGImageRef newImage = CGBitmapContextCreateImage(newContext); 

    /*We release some components*/
    CGContextRelease(newContext); 
     CGColorSpaceRelease(colorSpace);

     /*We display the result on the custom layer*/
    /*self.customLayer.contents = (id) newImage;*/

    /*We display the result on the image view (We need to change the orientation of the image so that the video is displayed correctly)*/
    UIImage *image= [UIImage imageWithCGImage:newImage scale:1.0 orientation:UIImageOrientationRight];
    self.capturedView.image = image;

    /*We relase the CGImageRef*/
    CGImageRelease(newImage);
}

在调用 CGBitmapContextCreate 。它总是返回 NULL 指针。因此，该函数的其余部分都不起作用。无论我似乎传递它，该函数返回null。我不明白为什么。

the code seems to work fine up until the call to CGBitmapContextCreate. it always returns a NULL pointer. so consequently none of the rest of the function works. no matter what i seem to pass it the function returns null. i have no idea why.

推荐答案

传递baseAddress的方式假定图像数据的格式为

The way that you are passing on the baseAddress presumes that the image data is in the form

ACCC

（其中C是一些颜色成分，R || G || B）。

( where C is some color component, R || G || B ).

如果您已设置AVCaptureSession以原始格式捕获视频帧，那么您很可能会以平面YUV420格式恢复视频数据。 （参见：链接文本）为了完成您在此处尝试执行的操作，可能最简单的方法是指定您希望在kCVPixelFormatType_32RGBA中捕获的视频帧。如果您以非平面格式捕获视频帧，Apple建议您捕获kCVPixelFormatType_32BGRA中的视频帧，其原因没有说明，但我可以合理地假设是出于性能考虑。

If you've set up your AVCaptureSession to capture the video frames in native format, more than likely you're getting the video data back in planar YUV420 format. (see: link text ) In order to do what you're attempting to do here, probably the easiest thing to do would be specify that you want the video frames captured in kCVPixelFormatType_32RGBA . Apple recommends that you capture the video frames in kCVPixelFormatType_32BGRA if you capture it in non-planar format at all, the reasoning for which is not stated, but I can reasonably assume is due to performance considerations.

警告：我没有这样做，并且假设访问这样的CVPixelBufferRef内容是构建图像的合理方法。我无法保证这实际上有效，但我/可以/告诉你，由于您（可能）捕获视频帧的像素格式，您现在可靠地执行操作的方式将无法正常工作。

Caveat: I've not done this, and am assuming that accessing the CVPixelBufferRef contents like this is a reasonable way to build the image. I can't vouch for this actually working, but I /can/ tell you that the way you are doing things right now reliably will not work due to the pixel format that you are (probably) capturing the video frames as.

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