-
Unexpected CC filter behavior after chromakeying clip
I recently was given a project to finish that was cut by another editor. The project contained several greenscreen interviews that the editor had attempted to key. The quality of the keys was poor, and I ended up needing to redo all of the keys myself. I usually do my keying in Combustion, but in this particular case I didn’t have the luxury of enough time to do this. Fortunately, the quality of the greenscreen footage was very good (well-lit greenscreen and talent shot on DVCPRO HD @ 1080p), so I was able to pull a decent key using FCP’s chromakey filter. Unfortunately FCP’s green spill suppression filter was awful (it noticeably darkened the rim of the subject instead of simply desaturating it), so I had to roll my own despill filter by using a 3-way CC filter with the “limit effect” option selected. Here’s where it got strange.
I added a 3-way CC filter to the clip as the final filter in the chain. The filters added to the greenscreen front clip were:
4:2:2 color smoothing > chromakey > 3-way CC (used as despill filter)
Strangely, when I enabled the “limit effect” option in the CC filter and narrowed the operating range to the spill color (which I then partially desaturated and hue shifted), suddenly the original greenscreen background reappeared, albeit as a grey background due to the desaturation. I thought this behavior was odd, since I would expect the filter to affect the clip after the result of the previous filters in the chain, not the original pre-keyed clip. Somehow, the CC filter seemed to be preempting the chromakey filter even though it was last in the chain.
I tried to work around this quirk by nesting the front clip into itself and then applying the despill (CC) filter, but the same thing happened again. The only way I could get around this behavior was to nest the front clip (subject) and the background clip, then add the despill CC to the nested sequence. This was far from preferable as the color suppression affected both clips in the nested comp instead of just the foreground clip. Fortunately in this case the background clip didn’t contain any green, so even though the despill CC was affecting the nested comp, it only appeared to be affecting the front clip (talent).
Maybe I’m just too used to the logic of a node-based workflow, but it strikes me as odd that the CC filter behaved this way when “limit effect” was enabled despite its position as the last filter in the chain. I double checked to make sure that the proper output toggle was selected in the CC filter (i.e. not matte or original), but still no dice. Any thoughts on why the CC filter might behave this way? I found the workaround to be very cumbersome and time consuming, but it ended up working out OK in this particular case.
If I’m not explaining myself very well, please ask for clarification and I’ll try to put together a diagram or a screencap. Thanks in advance.
-
4 Replies
-
In FCP, the bottom filter acts on the one above it. I never use FCP’s keyer so don’t know its vagaries. The Primatte keyer in Motion is excellent. That might have worked better for you. Another approach might be to export the FCP-keyed layer using the Animation codec to preserve the alpha channel, and then put your supression CC on that after importing it and replacing the original track, although, that’s probably as time consuming as the method you described.
John
MacPro 8-core 2.8GHz 8 GB RAM OS 10.5.5 QT7.5.5 Kona 3 Dual Cinema 23 ATI Radeon HD 3870, 24″ TV-Logic Monitor
ATTO ExpressSAS R380 RAID Adapter, PDE Enclosure with 8-drive 6TB RAID 5Final Cut Studio 2 (up to date)
Pro Tools HD w SYNC IO, Yamaha DM1000, Millennia Media HV-3C, Neumann U87, Schoeps Mk41 mics, Genelec Monitors, PrimaLT ISDN
-
[John Fishback] “In FCP, the bottom filter acts on the one above it.”
I understood this to be the case, but for some reason the CC filter wasn’t following the typical pattern.
[John Fishback] “. The Primatte keyer in Motion is excellent. That might have worked better for you.”
If I have the time to do keying outside of FCP, I’d ordinarily just use Combustion, but thanks for the suggestion.
[John Fishback] “Another approach might be to export the FCP-keyed layer using the Animation codec to preserve the alpha channel, and then put your supression CC on that after importing it and replacing the original track, although, that’s probably as time consuming as the method you described. “
I had considered that method, but in the interests of time, went with the solution I described. To be honest, I was quite surprised that I was able to get as good of a result with the FCP keyer as I did.
-
Hi Alan
Nest the clip with the 422 and the CK, then apply the Spill Supressor on the nest.
Don’t nest the background.
Rafael -
[Rafael Amador] “Nest the clip with the 422 and the CK, then apply the Spill Supressor on the nest.
Don’t nest the background. “That was the first thing I tried, and it didn’t work. I can’t explain why it doesn’t work, but it doesn’t. That’s the whole point of my post – it just doesn’t make sense.
Reply to this Discussion! Login or Sign Up