Hello,
I've done some more research and have come to the conclusion that
Quartz QCRenderer must be performing color correction (or
distortion, depending on your pt of view) under 10.4. (I'd love
to be wrong about this - really).
I'm wondering if anyone has anything they can add to this, or even
better a "oh yeah, do XYZ and you might find it'll work". I've
created a reasonably small test harness that demonstrates the
problem. It simply grabs the screen and puts it into a
SampleCIView.
Here's what I've discovered:
1) The most basic test. Clip a 128x128 area around the mouse (out
of the CVPixelBufferRef that contains the image from the screen).
Composite this back onto the final image before it's passed to the
SampleCIView, but at an offset y + 2 (so that we can see that the
compositing is taking place). Indeed, we can see a bit of the
image being composited on and the colors are correct.
Note: The primary reason for testing this was to check that my own
compositing code wasn't introducing the color change.
2) Do the same as (1) above, but before compositing pass the
128x128 buffer into a "do nothing" quartz patch. This patch takes
a CIImage as input, transforms it (upside down) using an Affine
Transform and spits it out again. It's got a (1) Clear and (2)
Billboard of size 2.0. I'd not expect this to have any real
effect on the image. What I see however is a lightening of the
128x128 image when it is composited.
Is it the case that all ye who enter the realm that is QCRenderer
on 10.4 should abandon all hope (of getting color correct)?
BTW: This code works fine under 10.5.
I've posted a full example, with controls to disable the QC part
(so, perform step (1) above) and also the offset. So that whoever
wants to can see the issues easily. I'm happy to raise a radar
for this if it's appropriate, but I'd like to know if I'm doing
something silly/stupid first.
http://downloads.shinywhitebox.com/QCCompositingSpike.zip (for
10.4/5, XCode 2.5).
Oh, the included qtz patch does more than just "nothing". It's a
nice little splash of water :-)
--
Regards,
Neil Clayton, http://shinywhitebox.com
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