# Differences between Region and Channel Tone Curves



## StarkmanAlive (Dec 28, 2014)

Greetings all,

Two questions:

1.  I use the region segment of the Tone Curve, the one you are free to create the curve as you like, all the time; a lot of times to create an S curve. I'm a bit confused, however, as to when to use the channel curve, the one where curve adjustment is restricted. The available sliders in this curve do not match exactly with the sliders in the Basic panel, and, further, adjusting the sliders that are the same (e.g., Highlights, Shadows) in the Channel curve do not effect the same results as the same named sliders in the Basic Panel.
These channel curve issues came to my attention after observing some presets I have that utilize the channel curve.
So, is there a quick understanding of what the channel curve sliders are geared for? How do you folks use them?

2.  Also in the Channel curve are the individual RGB sliders; when do you folks find tweaking these to be important. How does tweaking these differ than using the HSL sliders?

Thanks very much,

Starkman


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## Victoria Bampton (Dec 29, 2014)

The curves with the sliders are called Parametric curves.  They work just like the Point Curves (the other free one), except they're limited so you can't make the photo look too awful. Use whichever you're comfortable with.

HSL focuses on adjusting specific color range, whereas RGB curves are more generalized.  Most people won't tweak them very often though.


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## StarkmanAlive (Dec 29, 2014)

Victoria Bampton said:


> The curves with the sliders are called Parametric curves.  They work just like the Point Curves (the other free one), except they're limited so you can't make the photo look too awful. Use whichever you're comfortable with.
> 
> Yeah, that much I figured, but what's puzzling (looking at a few OnOne presets I have) is why use the Parametric instead of the free curve, and further, why use both at the same time (which is what some of those OnOne presets do)?
> 
> ...


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## Conrad Chavez (Dec 29, 2014)

StarkmanAlive said:


> 1.  I use the region segment of the Tone Curve, the one you are free to create the curve as you like, all the time; a lot of times to create an S curve. I'm a bit confused, however, as to when to use the channel curve, the one where curve adjustment is restricted. The available sliders in this curve do not match exactly with the sliders in the Basic panel, and, further, adjusting the sliders that are the same (e.g., Highlights, Shadows) in the Channel curve do not effect the same results as the same named sliders in the Basic Panel.


They don't match because they provide different choices. The Tone Curve is a traditional, direct type of adjustment (Take any pixels at 45%, make them 52% instead). But the Basic Develop sliders have an additional degree of intelligence and judgment built into them with the goal of retaining visual detail. For example, the Highlights slider calculates highlight recovery that involves local contrast adjustments behind the scenes. The Shadows slider is similar, not just lightening dark tones but also enhancing contrast of shadow details. Because the sliders are engineered to help make images look better than just a curve, it's usually good to use those first. But when you want to change values without Lightroom adding the other enhancements, the Tone Curve is better. If you want more details, here's an article I wrote about the differences: Editing Highlights and Shadows in Adobe Lightroom and Camera Raw

That might explain why OnOne uses both in their preset, if they consciously intended for each adjustment to have its unique effect. But they may have simply played around with controls until they got the effect they were after. Nothing wrong with either approach.



StarkmanAlive said:


> 2. Also in the Channel curve are the individual RGB sliders; when do you folks find tweaking these to be important. How does tweaking these differ than using the HSL sliders?


The RGB tone curve lets you adjust each of those channels anywhere in the tonal range. Want to make shadows less blue? You can drag down the shadow part of the blue Tone Curve but maintain the levels of blue in the midtones and highlights.

You can't do that with the HSL sliders because they move the entire color around; you can't target a tonal range with them. But some adjustments are a lot easier with the HSL sliders than with the Tone Curve. So again, the two sets of controls isn't redundant, it's more choices.


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## StarkmanAlive (Dec 30, 2014)

Ding, ding, ding! Got it, Conrad! Thanks very much.

Not having a graphic artist's eye (drawing circles is challenging), the obvious isn't usually obvious in this arena. But I can see now how the sliders in the point curve create different, less aggressive changes, if you will, than the sliders in the Basic panel. And gee, how is it I missed the bit about area-particular tonal range adjustments using the individual RGB channels? I mean, duh! That's the point of the curve, right! (On the other hand, it was VERY obvious — and there isn't a big enough font to stress "very" — that I was not to go with Photoshop but to go with Lightroom instead. No brainer there!)

Well, anyway, it makes sense, and as it makes more sense I am getting much better at putting Lightroom to use. 

Thanks again,

Starkman


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## pdxrjt (Jan 1, 2015)

Conrad,  thanks for the link to the article.  Looks great.


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