AVFoundation - 从Y平面获取灰度图像（kCVPixelFormatType_420YpCbCr8BiPlanarFullRange） [英] AVFoundation - Get grayscale image from Y plane (kCVPixelFormatType_420YpCbCr8BiPlanarFullRange)

问题描述

我正在使用AVFoundation拍摄视频，我正在以 kCVPixelFormatType_420YpCbCr8BiPlanarFullRange 格式录制。我想直接从YpCbCr格式的Y平面制作灰度图像。

I'm using AVFoundation to take a video and I'm recording in kCVPixelFormatType_420YpCbCr8BiPlanarFullRange format. I want to make grayscale image directly from the Y plane of the YpCbCr format.

我试图通过调用 CGBitmapContextCreate CGContextRef >，但问题是，我不知道选择什么colorspace和pixelformat。

I've tried to create CGContextRef by calling CGBitmapContextCreate, but the problem is, that I don't know what colorspace and pixelformat to choose.

- (void)captureOutput:(AVCaptureOutput *)captureOutput 
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer 
       fromConnection:(AVCaptureConnection *)connection 
{       
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer); 
    CVPixelBufferLockBaseAddress(imageBuffer,0);        

    /* Get informations about the Y plane */
    uint8_t *YPlaneAddress = CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 0);
    size_t bytesPerRow = CVPixelBufferGetBytesPerRowOfPlane(imageBuffer, 0);
    size_t width = CVPixelBufferGetWidthOfPlane(imageBuffer, 0);
    size_t height = CVPixelBufferGetHeightOfPlane(imageBuffer, 0);

    /* the problematic part of code */
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();

    CGContextRef newContext = CGBitmapContextCreate(YPlaneAddress,
    width, height, 8, bytesPerRow, colorSpace, kCVPixelFormatType_1Monochrome);

    CGImageRef newImage = CGBitmapContextCreateImage(newContext); 
    UIImage *grayscaleImage = [[UIImage alloc] initWithCGImage:newImage];

    // process the grayscale image ... 
}

当我运行上面的代码时，我遇到了这个错误：

When I run the code above, I got this errors:

<Error>: CGBitmapContextCreateImage: invalid context 0x0
<Error>: CGBitmapContextCreate: unsupported parameter combination: 8 integer bits/component; 16 bits/pixel; 1-component color space; kCGImageAlphaPremultipliedLast; 192 bytes/row.

PS：对不起我的英语。

PS: Sorry for my english.

推荐答案

如果我没弄错，你不应该通过 CGContext 。相反，你应该创建一个数据提供者，然后直接创建图像。

If I'm not mistaken, you shouldn't go via a CGContext. Instead, you should create a data provider and then directly the image.

你的代码中的另一个错误是使用 kCVPixelFormatType_1Monochrome 常数。它是视频处理（AV库）中使用的常量，而不是Core Graphics（CG库）中使用的常量。只需使用 kCGImageAlphaNone 即可。每个像素需要一个单独的组件（灰色）（而不是RGB的三个）来自色彩空间。

Another mistake in your code is the use of the kCVPixelFormatType_1Monochrome constant. It's a constant used in video processing (AV libraries), not in Core Graphics (CG libraries). Just use kCGImageAlphaNone. That a single component (gray) per pixel is needed (instead of three as for RGB) is derived from the color space.

它可能如下所示：

CGDataProviderRef  dataProvider = CGDataProviderCreateWithData(NULL, YPlaneAdress,
      height * bytesPerRow, NULL);
CGImageRef newImage = CGImageCreate(width, height, 8, 8, bytesPerRow,
      colorSpace, kCGImageAlphaNone, dataProvider, NULL, NO, kCGRenderingIntentDefault);
CGDataProviderRelease(dataProvider);

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