I am trying to manipulate an image using a chain of CIFilters, and then examine each byte of the resulting image (bitmap). Long term, I do not need to display the resulting image (bitmap) -- I just need to "analyze" it in memory. But near-term I am displaying it on screen, to help with debugging.

I have some "bitmap examination" code that works as expected when examining the NSImage (bitmap representation) I use as my input (loaded from a JPG file into an NSImage). And it SOMETIMES works as expected when I use it on the outputBitmap produced by the code below. More specifically, when I use an NSAffineTransform filter to create outputBitmap, then outputBitmap contains the data I would expect. But if I use a CILineOverlay filter to create the outputBitmap, none of the bytes in the bitmap have any data in them. I believe both of these filters are working as expected, because when I display their results on screen (via outputImageView), they look "correct." Yet when I examine the outputBitmaps, the one created from the CILineOverlay filter is "empty" while the one created from NSAffineTransfer contains data. Furthermore, if I chain the two filters together, the final resulting bitmap only seems to contain data if I run the AffineTransform last. Seems very strange, to me???

My understanding (from reading the CI programming guide) is that the CIImage should be considered an "image recipe" rather than an actual image, because the image isn't actually created until the image is "drawn." Given that, it would make sense that the CIimage bitmap doesn't have data -- but I don't understand why it has data after I run the NSAffineTransform but doesn't have data after running the CILineOverlay transform? Basically, I am trying to determine if creating the NSCIImageRep (ir in the code below) from the CIImage (myResult) is equivalent to "drawing" the CIImage -- in other words if that should force the bitmap to be populated? If someone knows the answer to this please let me know -- it will save me a few hours of trial and error experimenting!

Finally, if the answer is "you must draw to a graphics context" ... then I have another question: would I need to do something along the lines of what is described in the Quartz 2D Programming Guide: Graphics Contexts, listing 2-7 and 2-8: drawing to a bitmap graphics context? That is the path down which I am about to head ... but it seems like a lot of code just to force the bitmap data to be dumped into an array where I can get at it. So if there is an easier or better way please let me know. I just want to take the data (that should be) in myResult and put it into a bitmap array where I can access it at the byte level. And since I already have code that works with an NSBitmapImageRep, unless doing it that way is a bad idea for some reason that is not readily apparent to me, then I would prefer to "convert" myResult into an NSBitmapImageRep.

CIImage * myResult = [transform valueForKey:@"outputImage"]; 
NSImage *outputImage;
NSCIImageRep *ir = [NSCIImageRep alloc];
ir = [NSCIImageRep imageRepWithCIImage:myResult];
outputImage = [[[NSImage alloc] initWithSize:
                              NSMakeSize(inputImage.size.width, inputImage.size.height)]
                             autorelease];
                    [outputImage addRepresentation:ir];
[outputImageView setImage: outputImage];
NSBitmapImageRep *outputBitmap = [[NSBitmapImageRep alloc] initWithCIImage: myResult];

Thanks, Adam