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Keying out white... Trickier than usual

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Dylan Hargreaves
Keying out white... Trickier than usual
on Jun 24, 2015 at 6:10:35 pm

Hi folks,

Trying to key out the white background of some stock footage of a goldfish, so it's swimming on black. I've tried a few methods and none are working well enough - luma key, luma matting, extract, Colorama output phase, (as per a sky replacement.)

The problem is, the goldfish fins are very whispy and its underside is pretty bright, so it's either posterizing nastily or leaving a big white outline - even with a choker.

Am I onto a loser here? Is it time to find some alternative stock, or is there one last solution that I've missed?

Thanks in advance!

D


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Walter Soyka
Re: Keying out white... Trickier than usual
on Jun 25, 2015 at 12:40:20 am

Without seeing the footage, it's tough to tell, but...

You know how you can use UnMult [link] to generate alpha from black? You can do it with white, too. You just need to make an UnMult Sandwich: Invert, UnMult, Invert.

Sometimes it's nice to top your UnMult sandwich with a little Levels (Alpha channel).

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive [twitter]   |   RenderBreak [blog]   |   Profile [LinkedIn]


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Dylan Hargreaves
Re: Keying out white... Trickier than usual
on Jun 25, 2015 at 9:02:08 pm

Thanks Walter - good to know for next time!

Ended up going for quite a radical technique:

1. Went to pet store

2. Purchased goldfish & tank

3. Shot goldfish against black background

4. Voila

And now my kids have a fish!


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Walter Soyka
Re: Keying out white... Trickier than usual
on Jun 27, 2015 at 4:06:34 pm

[Dylan Hargreaves] "3. Shot goldfish against black background"

Well, that's cheating :)

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive [twitter]   |   RenderBreak [blog]   |   Profile [LinkedIn]


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