title: convert CMSampleBufferRef to UIImage
body: <p>I'm captuting video with AVCaptureSession.
  But I would like to convert the captured image to an UIImage.</p>
  
  <p>I found some code on Internet:</p>
  
  <pre><code>- (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);
  }
  </code></pre>
  
  <p>But I got some errors:</p>
  
  <blockquote>
  <pre><code>Jan 17 17:39:25 iPhone-4-de-XXX ThinkOutsideTheBox[2363] &lt;Error&gt;: 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] &lt;Error&gt;: CGBitmapContextCreateImage: invalid context 0x0
  2013-01-17 17:39:25.896 ThinkOutsideTheBox[2363:907] image &lt;UIImage: 0x1d553f00&gt;
  Jan 17 17:39:25 iPhone-4-de-XXX ThinkOutsideTheBox[2363] &lt;Error&gt;: CGContextDrawImage: invalid context 0x0
  Jan 17 17:39:25 iPhone-4-de-XXX ThinkOutsideTheBox[2363] &lt;Error&gt;: CGBitmapContextGetData: invalid context 0x0
  </code></pre>
  </blockquote>
  
  <p>EDIT:
  I also use the UIImage to get the rgb color:</p>
  
  <pre><code>-(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&lt;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);
  
  }
  </code></pre>