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Adjusting only luminance with the color wheels? Always a good idea?

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Richard Swearinger
Adjusting only luminance with the color wheels? Always a good idea?
on Sep 2, 2018 at 4:08:43 pm

While using the primaries wheels to adjust the scene brightness, how do you decide whether to change YRGB or only adjust the luminance channel?*

I was taught that changing only the luminance would help prevent color shifts, but there's a lot of bad information out there so I wanted to ask actual experts.

Thanks
RS


* If you hold the option key while spinning a wheel, changes affect only the luminance channel.



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Marc Wielage
Re: Adjusting only luminance with the color wheels? Always a good idea?
on Sep 3, 2018 at 8:52:44 am

[Richard Swearinger] "While using the primaries wheels to adjust the scene brightness, how do you decide whether to change YRGB or only adjust the luminance channel?* I was taught that changing only the luminance would help prevent color shifts, but there's a lot of bad information out there so I wanted to ask actual experts. "
I've never heard this in my life, at least in the past few decades. If anything, I think you can get into trouble with Luma-only changes since the scene's chroma is unaffected, which can lead to odd saturation issues.

The big panels has Luma-only knobs for Lift / Gamma / Gain, but I only use those for "problem" situations. I will say that if you're serious about color, you should invest in some kind of control surface and get used to the feel of what the knobs do and how to put the levels where you need them to be. As more than one person has observed, just setting up the basic core of the image to start with takes some time and patience to determine.

There's roughly a dozen ways to change overall brightness or level in Resolve, and deciding which way to do it is something you can only get with experience. Matching is a separate problem and a separate skill.


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Joseph Owens
Re: Adjusting only luminance with the color wheels? Always a good idea?
on Sep 3, 2018 at 5:40:32 pm

[Richard Swearinger] "I was taught that changing only the luminance would help prevent color shifts"

Seems like an incomplete understanding of the principle of "constant luminance" which is a strength of the (small-d original) daVinci-originated algorithm. If you simply adjust RGB without regard to what that is doing to the YCbCr matrix, you will get a non-uniform locus owing to the power-function distribution within the colorspace. Think about how Y' (gamma-weighted) is calculated as a single weighted-value based on the contributing tristimulus components and you will start down the right path toward grasping how you would really need to adjust the overall balance of all three in order to keep their relative vectors coherent in order to achieve the same hue rendition within a changed brightness range. Luma/gamma weighting also affects the perceived saturation of a color value, so it isn't just a mathematical problem, either.

Color correction is one of the most non-linear pursuits that you can attempt. Most people think of the CIE colorspace as a horseshoe, but that is just in 2-D representation. Luminance-weighted, it looks like a lopsided ski-hill full of moguls.

jPo, CSI

"I always pass on free advice -- its never of any use to me" Oscar Wilde.


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Richard Swearinger
Re: Adjusting only luminance with the color wheels? Always a good idea?
on Sep 3, 2018 at 7:00:54 pm

So it other words it is not like editing in LAB where adjusting the L value doesn’t affect the other two channels. (What I’m learning is that Photoshop techniques just doesn’t seem to apply very often to Resolve.)


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Chris Wright
Re: Adjusting only luminance with the color wheels? Always a good idea?
on Sep 6, 2018 at 1:14:30 am

use resolve's LAB mode






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Marc Wielage
Re: Adjusting only luminance with the color wheels? Always a good idea?
on Sep 9, 2018 at 3:09:34 am

[Chris Wright] "use resolve's LAB mode"
You might use this for special situations where you need some really precise, targeted adjustment, but in the real world, we rarely have the time to get that super-tweaky. On an episodic TV project, even if we take 1 minute for correction per shot, and there's (say) 700 shots, that's over 12 hours just for correction. And the client still needs to view it and approve it. For a commercial... sure, if you have 10 shots in a 5-6-hour session, it's possible and expected to get very, very tweaky. But not for everything, certainly not for bread-and-butter situations like the o.p. is describing.

Sometimes, keeping it simple is better.


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