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Compositing issue in FCPX

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Daniel Zimmerman
Compositing issue in FCPX
on Jun 17, 2015 at 9:28:03 pm

I'm experiencing an annoying issue when compositing in FCPX 10.2.1. I first chroma keyed an uncompressed SD (720x486, interlaced) clip in AE. I then exported the keyed clip to Prores 4444 (RGB+Alpha). After dragging the keyed clip to an empty timeline in FCPX, I can see that the clip looks good. But as soon as I place a background image underneath the keyed clip, the quality of the latter degrades, like low resolution video, and what's worse, there's very noticeable random color dots. If I move the background image away from the playhead, the keyed clip appears normal again, with black background of course. But if I do the same thing in AE, it looks perfect, no degradation or color dots.

In FCPX, I tried setting the blend mode of the keyed clip to Alpha Add and Premultiplied Mix, I also tried exporting the keyed clip in AE as straight Alpha instead of premultiplied, still couldn't solve the problem. In AE, I also tried 16bpc and 32bpc.

Sometimes, when I first place the background image beneath the keyed clip in FCPX, the composite looks great. But it soon goes back to the degraded look again. This problem is not just in viewer. The rendered version looks the same - degraded and color dots.

I was wondering if someone can shed some light on this issue. I shot the footage uncompressed hoping to generate a great key, only to find FCPX doesn't recognize uncompressed. Now going the AE-FCPX route doesn't seem to work, either. Really annoying. Thanks for reading.

Daniel


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David Gregorio
Re: Compositing issue in FCPX
on Jun 18, 2015 at 3:05:43 am

[Daniel Zimmerman] "Sometimes, when I first place the background image beneath the keyed clip in FCPX, the composite looks great. But it soon goes back to the degraded look again."

By this description, it almost seems like FCPX does it properly in real-time but messes up when it background renders the timeline. I'm wondering if by placing the Prores 4444 clip in first, it's setting the timeline resolution incorrectly. You might try manually setting the timeline resolution first.


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Daniel Zimmerman
Re: Compositing issue in FCPX
on Jun 18, 2015 at 4:24:04 pm

Thanks for helping out, David. I actually tried both methods. First I manually set project video properties to "NTSC SD, 720x486, 29.97i". Didn't work. Then I set project video properties to "set based on first video clip". No difference.

Also, it doesn't matter what background I put beneath the keyed clip, be it a still image or a video clip. But if I place a similarly AE-generated keyed clip beneath the original keyed clip, there will be less random color dots.

Daniel


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Daniel Zimmerman
Re: Compositing issue in FCPX
on Jun 19, 2015 at 2:23:21 am

Just shot an uncompressed 10-bit 422 test video. This time around FCPX does recognize the footage (because it is 10-bit now instead of 8-bit). However, after applying the built-in "keyer" effect, the footage becomes blurred. Placing background image underneath the keyed footage doesn't cause the previous issues (degradation and color dots). But the footage looks blurry, even after rending the composite out as Prores 422.

Do the same thing in AE (using Keylight), and the result is beautiful, like before. Slightly worse in Premier Pro (using Ultra Key), possibly due to the keyer.

My preliminary conclusion - in terms of chroma keying and compositing, FCPX 10.2.1 probably isn't the best tool to use.


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Jacob Brown
Re: Compositing issue in FCPX
on Jun 19, 2015 at 7:26:08 pm

i've done a good bit of compositing in FCPX and never had a problem (other than transitions in composites never working)...

i wonder if you need to have project set to a 4444 color space though so it works with alpha channel? just a guess tho.


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Doug Metz
Re: Compositing issue in FCPX
on Jun 19, 2015 at 7:52:41 pm

You can work with alpha in FCPX regardless of project setting, but if you need your output file to retain transparency for compositing elsewhere, then you'd set the project to ProRes4444.

Doug Metz

Anode


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Daniel Zimmerman
Re: Compositing issue in FCPX
on Jun 21, 2015 at 7:25:14 am

Tried transcoding the previous 10-bit 422 uncompressed test shot to Prores 422. FCPX behaves normally. It works with the Prores 422 flawlessly. I can pull a clean key without the blur issue or the degradation and color dots. So this has become my preferred workflow.

How do you set a project to 4444 in FCPX? There doesn't seem to be a place for one to do so.

Thanks.


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