Converting CMSamppleBufferRef to UIImage is a common job we have to do when working with AVCaptureSession and AVCaptureVideoDataOutput. These snippets below acts as a reference for me and those who are interested :)

Here I convert to CGImageRef first. Converting CGImageRef to UIImage is simple with this line

[code language=”objc”]


UIImage *image = [UIImage imageWithCGImage:cgImageRef];


[/code]

Remember that imageWithCGImage has autorelease, so we must wrap it into @autoreleasepool, even though we’re using ARC

[code language=”objc”]


@autoreleasepool


{


// Code that return autorelease obj


}


[/code]

[code language=”objc”]

• (CGImageRef)imageFromSampleBuffer:(CMSampleBufferRef)sampleBuffer
  
  
  {
  
  
  // 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 base address
  
  
  void *baseAddress = CVPixelBufferGetBaseAddressOfPlane(imageBuffer, 0);

  
  
  

  // 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);

  
  
  

  // We should return CGImageRef rather than UIImage because QR Scan needs CGImageRef
  
  
  return quartzImage;
  
  
  }
  
  
  [/code]

This snippet below both converts to CGImageRef and perform cropping. It is taken from ZXingObj (ZXingObj/client/ZXCGImageLumianceSource.m)

[code language=”objc”]

• (CGImageRef)createImageFromBuffer:(CVImageBufferRef)buffer
  
  

    left:(size_t)left
  
  
     top:(size_t)top
  
  
   width:(size_t)width
  
  
  height:(size_t)height {
  
  
  

  int bytesPerRow = (int)CVPixelBufferGetBytesPerRow(buffer);
  
  
  int dataWidth = (int)CVPixelBufferGetWidth(buffer);
  
  
  int dataHeight = (int)CVPixelBufferGetHeight(buffer);
  
  
  

  if (left + width > dataWidth ||
  
  

  top + height > dataHeight) {
  
  
  

  [NSException raise:NSInvalidArgumentException format:@"Crop rectangle does not fit within image data."];
  
  
  }
  
  
  

  int newBytesPerRow = ((width4+0xf)>>4)<<4;

  
  
  

  CVPixelBufferLockBaseAddress(buffer,0);

  
  
  

  int8_t baseAddress =
  
  
  (int8_t )CVPixelBufferGetBaseAddress(buffer);

  
  
  

  int size = newBytesPerRowheight;
  
  
  int8_t bytes = (int8_t)malloc(size);
  
  
  if (newBytesPerRow == bytesPerRow) {
  
  
  memcpy(bytes, baseAddress+top*bytesPerRow, size);
  
  
  } else {
  
  
  for(int y=0; y
  

  memcpy(bytes+y*newBytesPerRow,
  
  
         baseAddress+left*4+(top+y)*bytesPerRow,
  
  
         newBytesPerRow);
  
  
  

  }
  
  
  }
  
  
  CVPixelBufferUnlockBaseAddress(buffer, 0);
  
  
  

  CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
  
  
  CGContextRef newContext = CGBitmapContextCreate(bytes,
  
  

                                            width,
  
  
                                            height,
  
  
                                            8,
  
  
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                                              newBytesPerRow,
  
  
                                            colorSpace,
  
  
                                            kCGBitmapByteOrder32Little|
  
  
                                            kCGImageAlphaNoneSkipFirst);
  
  
  

  CGColorSpaceRelease(colorSpace);
  
  
  

  CGImageRef result = CGBitmapContextCreateImage(newContext);

  
  
  

  CGContextRelease(newContext);

  
  
  

  free(bytes);

  
  
  

  return result;
  
  
  }
  
  
  [/code]

P/S: These only works if we set VideoDataOuput format type to BGRA

[code language=”objc”]


NSString key = (NSString)kCVPixelBufferPixelFormatTypeKey;


NSNumber value = [NSNumber numberWithUnsignedInt:kCVPixelFormatType_32BGRA];


NSDictionary videoSettings = [NSDictionary dictionaryWithObject:value forKey:key];


[dataOutput setVideoSettings:videoSettings];


[/code]