Adobe After Effects Forum
Compositing linear fire over log footage...
Compositing linear fire over log footage...
by Blase Theodore on Mar 8, 2008 at 2:14:17 am

I'm working with log dpx footage from film scan, and I'm compositing some footage of fire over the top. The fire footage is linear, so it doesn't have the range in the highlights that the log footage does.

I've just been doing a cineon converter effect on the log footage, leaving the fire alone, and then rendering everything out in log. Is there a better way to do this? Possibly working with the fire footage in log, instead of a log/lin lin/log conversion? I'm just concerned that I'm creating an unnecessary bottleneck in the range.

Thanks!
Blase


Re: Compositing linear fire over log footage...
by Darby Edelen on Mar 8, 2008 at 6:00:38 am

[Blase Theodore] "I've just been doing a cineon converter effect on the log footage, leaving the fire alone, and then rendering everything out in log. Is there a better way to do this? Possibly working with the fire footage in log, instead of a log/lin lin/log conversion? I'm just concerned that I'm creating an unnecessary bottleneck in the range."

In converting your DPX files from log->lin and then back from lin->log you shouldn't be losing any range. However, if your fire footage was not shot in a high-dynamic range format such as Cineon/DPX then it will not have the same dynamic range as your DPX footage.

If you want to see what this looks like at different exposures you can adjust the exposure preview at the bottom of the composition window. You should notice that the highlights in the DPX footage will maintain some brightness as you decrease the exposure, and the fire footage will not (it will appear to grow dull). Assuming you are working in 32bpc, you can try to change this by boosting the highlights of the fire layer into the superwhite range using levels, curves, exposure or another similar 32bpc capable color correction effect. The problem you may have is finding the right level for the highlights in the fire, I would be hesitant to suggest any sure fire way (no pun intended) to achieve the correct 'exposure' for the fire outside of looking at reference footage with fire... The second best option might be to find the brightest source in your DPX footage (is there a candle? a bright light?) and trying to guess at how much brighter (more overexposed) than this element the fire should be.

Use the exposure preview to check your work.

Darby Edelen
Designer
Left Coast Digital
Santa Cruz, CA


Re: Compositing linear fire over log footage...
by Blase Theodore on Mar 8, 2008 at 6:09:13 am

Wow, thanks for your very coherent answer :) That's exactly what I needed to know.







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