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Color and GPU Processing


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#1 Thomas Worth

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Posted 05 April 2008 - 08:04 AM

The big question I have about Color is the way it utilizes the GPU for processing. Since the GPU resides on the video card, how does that translate to other interfaces like the SDI interface (Aja, Blackmagic)? Is the system taking the processed data off the GPU and then sending it to the SDI interface? Clearly, having GPU processing affect only the DVI ports on the video card offers little value, since monitoring must be performed through an SDI interface without any interference by the Mac's graphics API or the video card's driver.

I've been playing with Color and am having trouble getting realtime 1080p output through the Blackmagic Multibridge. I can get realtime performance when external video is disabled, but utilizing SDI out for monitoring only gets me reliable 720p output. It looks like some type of bandwidth issue, since Color is clearly capable of processing the video in realtime. Even with NO color adjustment at all, 1080 output through the Blackmagic is stuttery.

I am using a Jan/2008 Mac Pro 8 core, with a 250MB/sec raid and an Nvidia 8800GT.

Any ideas?
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#2 tylerhawes

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Posted 09 April 2008 - 12:04 PM

Color renders on the GPU and then copies the pixels over the PCI Express bus to the framebuffer of your SDI card, so it is always using the GPU to make the image regardless of whether you're monitoring SDI, DVI, or just rendering.

I'm not sure why you're slowing down on SDI output, I can just say that on an 8-core here there is no difference in playback between SDI and DVI. We get realtime SDI with 2K full aperture with primary and some secondaries.
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#3 Thomas Worth

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Posted 16 April 2008 - 12:20 AM

Color renders on the GPU and then copies the pixels over the PCI Express bus to the framebuffer of your SDI card, so it is always using the GPU to make the image regardless of whether you're monitoring SDI, DVI, or just rendering.

I'm not sure why you're slowing down on SDI output, I can just say that on an 8-core here there is no difference in playback between SDI and DVI. We get realtime SDI with 2K full aperture with primary and some secondaries.

Thanks Tyler. What video card do you have installed in the Mac? I have been reading that Final Touch was optimized for ATI cards, so the fact that I'm using an Nvidia card may be the problem. Perhaps Apple hasn't optimized Color for the Nvidia GPU.
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#4 tylerhawes

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Posted 16 April 2008 - 01:04 PM

ATI X1900, which I believe is still the preferred card for Color. Check with your vendor to be sure...
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