FORUMS: list search recent posts

How to reduce qualifier chatter in areas of fine gradation ???

COW Forums : DaVinci Resolve

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
Michael McCune
How to reduce qualifier chatter in areas of fine gradation ???
on Oct 24, 2016 at 3:39:41 am

I frequently try to use windows and a qualifier to select skin tones for modification. Rarely works well.

It seems to have great potential but--as cruelly examplified in every carefully constructed online tutorial--only seems to work with discrete and clearly defined edges.

Usually there is a problem with chatter in areas of fine gradation. That is, the qualifier selection is deciding on a frame-by-frame basis whether a given pixel is included. Of course on playback the visual appearance is one of flickering, where the affected pixels show the applied adjustment or are excluded. Even small areas of flicker or chatter are visually obvious and sooo distracting.

Drives me nuts. There is, it seems, no amount of precision is qualifier settings that will stabilize this chatter, as it may be an actual variation in the original pixel levels.

But there must be a solution, such as the chatter adjustment in After Effects. In electronics, this age-old switching dilemma is addressed by adding hysteresis to the switch timing. Even thermostat settings at home have a "dead zone" of a degree or two to mitigate constant fast switching between states.

Rotoscoping is impractical for the usual reasons, especially for longer clips. Qualifiers would be great, it would seem, if there could be some further sophistication built in.

Or, perhaps--not the first time--I am missing something obvious and even embarrassing.

Please embarrass me with your wisdom!

Thanks, Mike

Return to posts index

Andy Winter
Re: How to reduce qualifier chatter in areas of fine gradation ???
on Oct 24, 2016 at 12:16:30 pm

hi mike...

Qualifications do work :). but of course, not all the time, as it depends on the area you want to qualify, on the state of the picture (codec, exposure etc.) and on you're approach of keying.

generally i ask myself: what did you try already? you can get rid of the flickering-issue by blurring the key. this should be the last step, because if you blur too much, you will see the soft "edges" of your qualification. try before to soften the H S and L. try the new clean black and clean white parameters etc.

you should also bear in mind that for a succesful key a balanced, kind of neutral picture helps a lot. if your whole picture has a green cast and you are trying to key out a green jacket, you might get in trouble. if your picture in general is very warm, you might get into trouble qualifying skin tones etc. try to key from a balanced picture and add the style after the keying.
if you are still experiencing flickering, you could also try to denoise the picture before.

and the list goes on and on and on...

Return to posts index

Michael McCune
Re: How to reduce qualifier chatter in areas of fine gradation ???
on Oct 25, 2016 at 10:36:01 am

Thanks, Marc and Andy; You asked about the source: it is Sony A7s into a Shogun as UHD ProRes 444 (though this Sony has only 8 bits, of course).

In short, you both seem to suggest that, yes, it can be made to work :).

And, as you both suggest, there usually is a way, perhaps requiring a few extra steps, to get a cleaner key. Both of you seem to point to handling the key itself, after the initial qualifier setup, and not simply taking the qualifier output as it might come off the clip.

Or creating a separate video grade for the purpose of pulling the key, such as, perhaps, a high contrast B&W version. Or perhaps a color adjusted version that tries to separate colors and tones. Perhaps LAB color might help here as it can quickly and dramatically separate colors in a scene along its two axes, blue-yellow and green-magenta. (Photoshop ACR additionally has a red-cyan axis: why not Resolve?)

(BTW, I have really gotten to like the Resolve temp and tint controls for fine adjustments: nice numeric handles along known axes. Quick and easy to eyeball the balance point for each axis. Color wheels are intuitive but a little fuzzy when attempting fine adjustments: like trying to type with gloves on.)

I understand that 12.5.2 has the ability to feed keys into the video input of a separate node for the purpose of massaging the key using the wider range of tools available in video as opposed to just the qualifier adjustments, including the new clean black and white controls, which I find to be the best adjustment tools.

And I haven't really given the 3D keyer a good chance yet: so that, too.

Regarding rotoscoping, why doesn't Resolve have a tool--used every day in Photoshop-- the venerable and reliable Magic Wand tool? It quickly can edge-detect shapes and show a marching ants selection for a mask. And it just as quickly allows for corrections. True, this is a quick solution that is usually refined further in Photoshop, but might be a great start for masking and rotoscoping. And, surprise, might be more than adequate in many situations.

And, Marc, you mentioned tracking. I have come to have a love-hate feeling about tracking. Fantastic when it works, but I--and others, it seems--have had projects crash repeatedly when it is unhappy. My half-baked theory is that this is a devilish database problem and it gets confused: lots of data.

And, BTW, I find the relatively tiny tracking window too constricting for comfort. How about a tear-off, re-sizable window? With a longer keyframe timeline? Easier control over scale adjustments? Tools to manipulate individual tracking keyframes? Yada Yada: stuff anyone would see. Next Resolve version?

OK, onward and upward with qualifiers: gotta be a reliable method.

Thanks, Marc and Andy. Mike

Return to posts index

Marc Wielage
Re: How to reduce qualifier chatter in areas of fine gradation ???
on Oct 25, 2016 at 8:21:59 am

I find the 3D keyer helps, plus tracking windows. 90% of the time, though, I'm not making a massive change -- I'm taking a little green or yellow of a face, or just trying to raise the overall luminance a few points.

What's the source material? I don't see any perceptual chatter from good solid 10-bit cameras. Note that it's also possible to just pull a key, then soften the key and change the color that way.

And I can and do rotoscope masks when necessary, just because you gotta do what the shot needs.

Return to posts index

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
© 2018 All Rights Reserved