Confused about Tone Curve: Parametric vs Point Curve

[Hmmokthen]

Hello, So unfortunately the agent and I struggled in our conversation and now I am left with 2 questions instead of 1:

#1 - Parametric curve is adjusting the brightness of ALL colours in the relevant tonal area. Point curve DOES THE EXACT SAME THING, the only difference being you can have up to 14? tonal areas whereas Parametric curve has 4, and Point Curve can boost/decrease brightness by a maximum of up to 4 large grids vs 2 large grids. -- Correct?

#2 - If Parametric curve and Point curve do the same thing, then why does only Point Curve have "refine saturation" slider?

thanks

[JohanElzenga]

#1 - More or less correct. A big difference is that the point curve has individual channels as well, so it is also a powerful color correction tool. The point curve used to be on its own, but because many people found it too challenging, Adobe added a simpler version.

#2 - No idea. Perhaps because the parametric curve is aimed at people who may not understand what the Refine Saturation slider does...

[Hmmokthen]

thanks. "A big difference is that the point curve has individual channels as well" — you are reffering to the "Red channel", "Green channel" and "Blue channel", not the "Point Curve" channel, correct?

[JohanElzenga]

Yes. If you select the red channel (click on the red dot above the curve), then moving this curve will affect the red channel of the image only. Try it to see how that works.

[Hmmokthen]

ive got the hang red channel. I think I might of had problems in my conversation with the Adobe agent perhaps because ive been referring to point curve as solely that 2nd channel up top, when you said "point curve has individual channels as well" does that mean when you say "point curve" you are actually referring to all those 4 channels (Point curve — all colours, red channel, blue channel, green channel)?

[JohanElzenga]

ive got the hang red channel. I think I might of had problems in my conversation with the Adobe agent perhaps because ive been referring to point curve as solely that 2nd channel up top, when you said "point curve has individual channels as well" does that mean when you say "point curve" you are actually referring to all those 4 channels (Point curve — all colours, red channel, blue channel, green channel)?

By @Hmmokthen

Yes. All those four channels are part of the point curve.

[Hmmokthen]

that doesnt make sense to me, because every one of the 5 channels in Tone Curve act independant of each other and have a cumulative effect on the image. Secondly, the channels are not labelled "point curve - red channel", "point curve - green channel" etc. they're just labelled "red channel", "green channel"

[JohanElzenga]

I'm sorry that it does not make sense to you, but this is the way it is. Perhaps this helps you to understand it (the article shows the old UI of the curves panel, but that does not change anything as far as understanding what curves do is concerned): 

https://www.theclickcommunity.com/blog/lightroom-color-curves/

[Conrad_C]

that doesnt make sense to me, because every one of the 5 channels in Tone Curve act independant of each other and have a cumulative effect on the image. Secondly, the channels are not labelled "point curve - red channel", "point curve - green channel" etc. they're just labelled "red channel", "green channel"

By @Hmmokthen

OK, so maybe Adobe didn’t do the best job labeling the tool tips. But you can see the difference more obviously by looking at how they designed the icons:

The Composite/Red/Green/Blue options controlled with a Point Curve all have the same icon: A circle that can have a dot in it.

The Parametric Curve has a unique double-S icon that clearly shows it is not in the same group as the other four circles.

It’s clear that you can apply adjustments using any combination of those curve options and they will all be applied together, because of the dot that appears below a circle when it has an adjustment.

(If you want to be picky about the UI, you could argue that they should not have used a design that looks so close to traditional “radio buttons” because the radio button design has historically meant that the circle with the dot in it is the only one in the set that applies it settings. But the dots under the circles address that, sort of.)

[Hmmokthen]

Agreed that Parametric Curve can be easily told its different than the others. By the looks of things it seems I should refer to the other 4 channels as: Point Curve - Composite ("Point curve"), Point Curve - Reds ("Red channel"), Point Curve - Greens ("Green channel"), Point Curve - Blues ("Blue channel"). 

[Conrad_C]

I don't know the exact answer, but the history might provide some insight. 

Lightroom Classic 1.0 was released in 2007, and its Point Curve is probably based on the Curves in Photoshop that existed for many years before that. So the Point Curve is the starting point. It has the longest history by far, is widely taught, and is a standard tool now found in many other Photoshop-like apps.

The Parametric Curve was introduced later, in Lightroom and Camera Raw but not in Photoshop. I think the Parametric Curve was marketed as an easier way to use a curve, because instead of having to learn how to manually decide where to place the points and how to move them, you can just move some labeled sliders.

But they basically do the same thing. When you edit the curve, each tonal level starts at one value, and your edit shifts them to another value set by the curve. That's why on the Point Curve, each point has an Input and Output value.

What about the Refine Saturation slider? I don’t know why it’s only in the Point Curve, but this is my guess: The Point Curve has always been the “pro” option, because it’s more difficult to understand and learn than the Parametric Curve or (in Photoshop) the Levels command. They might have decided that Refine Saturation should be in the curves type that’s more widely used by pros, and for now, they decided not to add it to the Parametric Curve because it’s more of the “easy” option. But again, that’s just my guess. Maybe they’re open to adding Refine Saturation to Parametric Curve later, but that isn’t something we users would know.

As JohanElzenga pointed out, another difference is that the Point Curve lets you separately edit each RGB channel. That is two advanced features that Point Curve has that Parametric Curve does not, contributing to the notion that Adobe might think Point Curve is the “pro” version and Parametric is the “easy” version.

[Hmmokthen]

cheers. So what is your recommended approach — use parametric curve and if I notice any difference in colour saturation, reset the channel and do it in point curve channel instead?

[Conrad_C]

That would work fine: If you think the Parametric curve is easier, start with that.

Then check the results. If they’re fine, you’re done and can move on to other edits.

If you need to solve more specific problems like saturation or per-channel adjustments, or if you need to shape the curve in a way that Parametric can’t, then you could try the Point curve instead. Another reason to learn the Point curve is so that you know how to use it in the countless other applications that have a Point curve, from scanning software to video editors as well as other image editors. In other words, learning the Point curve is a transferable skill.

[reproo2773183]

Pushing the curves around together doesn't respect the grey balance. Its more noticable in the midtones, so less noticable if you are applying a standard s-curve.

You also are potentially dealing with a hidden Tone Curve in the Camera Profile, being able to rein back unwanted Saturation is pretty cool.

Below Visually correct greyscale requires Cyan to follow a different path to Magenta and Yellow

In RGB Curves; Red is opposite to Cyan, Green is Opposite to Magenta, Blue is opposite to Yellow.