The Channel Combiner is unfortunately still only 8bit and will disregard any masks on a layer, so if you want to do an accurate unmult with higher bitdepth with native AE tools then you need to first in a precomp do your own Max RGB. 

Seperating the footage in 3 layers, shifting each color channel into each of the other channel to get a full Red a full Green and a full Blue, then comp them with the Lighten blend mode and you will get the MaxRGB for that image. This precomp you use as an secondary input in a Set Matte effect on the original image and set "use for matte" to "luminance", and end with using Remove Color Matting... So much easier if we had a simple native Unmult effect :-/

to make it a bit simpler to understand the steps above you can download an .aep file here:

https://adobe.ly/2JBrw30

Robert

2018-04-10 10:35 GMT+02:00 Chris Zwar <AE-List@media-motion.tv>:

Thanks for trying and sharing!

On 10 Apr 2018, at 6:32 pm, Roei Tzoref <AE-List@media-motion.tv> wrote:

Great. Channel Combiner followed by remove color matting give the precise result.

Thanks Chris. one more plugin I don't have to use :)

On Tue, Apr 10, 2018 at 5:59 AM, Chris Zwar <AE-List@media-motion.tv> wrote:

Oh Ok.  I haven’t looked at the AE preset, but I can see that the problem is that it is using the shift channels to copy the lightness value.  This isn’t correct, the better way to do it is to use the channel combiner plugin to copy the Max RGB value to the alpha channel.

Try using that instead of shift channels and see if you get different results.  

On 10 Apr 2018, at 11:37 am, Roei Tzoref <AE-List@media-motion.tv> wrote:

Thanks Chris, I have watched your tutorial a while back. this does not solve the problem with Ae's unmult though...

as I mentioned, Ae's Unmult preset, which simply does 2 things: Shift Channels with take alpha from lightness + remove color matting, is not a good tool for unmulting since it has a discoloring after effect which AFAIK cannot be avoided.

a simple test confirms this. examples here:

https://imgur.com/a/JoTb0

AFAIK, the only way to unmult accurately in Ae is to use any of these 3rd party plugins: Knoll Unmult, mekajik Unmult, VC Color Vibrance

On Tue, Apr 10, 2018 at 4:03 AM, Chris Zwar <AE-List@media-motion.tv> wrote:

Actually it’s the opposite.  If you simply copy the lightness into the alpha then the RGB is preserved entirely, but this isn’t accurate.  You need to use the remove colour matting plugin as well, which then takes the background colour into account and adjusts everything accordingly.

This video demonstrates what the remove colour matting plugin does and why it’s important:

https://www.provideocoalition.com/alpha-channels-good-bad-ugly/

On 10 Apr 2018, at 10:57 am, Roei Tzoref <AE-List@media-motion.tv> wrote:

Ae's Umult - Alpha from Lightness (Unmult) preset) unfortunately is not optimal since it has a discoloring result. it does not preserve the RGB information in it's entirety. I have seen not any way in Ae to unmult natively without this discoloring effect. a simple test is taking a black solid, adding a lens flare effect, then trying to unmult. 

another free option exists in the VC Color Vibrance plugin which is free by video copilot: 

https://www.videocopilot.net/blog/2016/02/color-vibrance-update-v1-06/

simply change the color to 0 to have no effect in color, and change "matte alpha" to "on"

On Tue, Apr 10, 2018 at 1:47 AM, Stephen van Vuuren <AE-List@media-motion.tv> wrote:

And if you want to mess around with more creative kind of options, Brian Moffit eons ago suggested a Shift Channels (Take Alpha from Luminance) and muck about the a levels effect to boost/lower alpha to taste.

-----Original Message-----
From: After Effects Mail List <AE-List@media-motion.tv>
Sent: Monday, April 9, 2018 6:04 PM
To: After Effects Mail List <AE-List@media-motion.tv>
Subject: Re: [AE] Unmult?

It’s not THAT cumbersome to do with standard AE tools… first you use the channel combiner, set the first option to Max RGB and the second to Lightness. Then use the “remove colour matting” plugin.  The combination of those two effects is the same as unmult.

> On 9 Apr 2018, at 11:43 pm, Byron Nash <AE-List@media-motion.tv> wrote:
>
> Looks like Red Giant put their unmult effect into legacy status and they have one in Universe now? What's the current pulse on which unmult effect to use? Is there another option these days?


+---End of message---+
To unsubscribe send any message to <ae-list-off@media-motion.tv>

+---End of message---+
To unsubscribe send any message to <ae-list-off@media-motion.tv>