gistfile1.m

// Get the data into a bitmap.
[self lockFocus];
rep = [[NSBitmapImageRep alloc] initWithFocusedViewRect:[self bounds]];
[self unlockFocus];

// Make an NSImage from our bitmap.
image = [[[NSImage alloc] initWithSize:[rep size]] autorelease];
[image addRepresentation:rep];

NSData  * tiffData = [image TIFFRepresentationUsingCompression: NSTIFFCompressionNone factor: 0.0f];
CIImage *backgroundCIImage = [[CIImage alloc] initWithData:tiffData];

CIContext *ciContext = [[NSGraphicsContext currentContext] CIContext];  
[ciContext drawImage:backgroundCIImage atPoint:CGPointZero fromRect:someRect];