Question

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

我在互联网上找到了一些代码：

- (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);
}

但是我遇到了一些错误：

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：我还使用UIImage来获得rgb颜色：

-(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);

}

Answer 1

您最好的选择是set the capture video data output's videoSettings到specifies the pixel format you want的字典，您需要将其设置为CGBitmapContext可以处理的RGB变体。

文档已a list of all of the pixel formats that Core Video can process。 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）可能更快。尝试使用在设备上，并比较帧速率。

Answer 2

您可以尝试使用此代码。

-(UIImage *) screenshotOfVideoStream:(CMSampleBufferRef)samImageBuff
  {
       CVImageBufferRef imageBuffer =  
         CMSampleBufferGetImageBuffer(samImageBuff);
       CIImage *ciImage = [CIImage imageWithCVPixelBuffer:imageBuffer];
       CIContext *temporaryContext = [CIContext contextWithOptions:nil];
       CGImageRef videoImage = [temporaryContext
                         createCGImage:ciImage
                         fromRect:CGRectMake(0, 0,
                         CVPixelBufferGetWidth(imageBuffer),
                         CVPixelBufferGetHeight(imageBuffer))];

       UIImage *image = [[UIImage alloc] initWithCGImage:videoImage];
       CGImageRelease(videoImage);
      return image;
}

对我有用。

Answer 3

如果有人像我一样期待 jpeg 图像，Apple 提供了简单的 API：

[AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:photoSampleBuffer];

和：

[AVCapturePhotoOutput JPEGPhotoDataRepresentationForJPEGSampleBuffer:photoSampleBuffer previewPhotoSampleBuffer:previewPhotoSampleBuffer]

将CMSampleBufferRef转换为UIImage

3 个答案: