The CA correction options are confusing for new RawTherapee users

[afontenot]

This issue is forked off from https://github.com/Beep6581/RawTherapee/issues/5719#issuecomment-617733843

I recently filed this issue because I couldn't get CA correction to work. It turns out the biggest cause of this was that I had accidentally left a CA setting enabled that I didn't even know existed, and it was making the problem much worse. The following describes how that happened.

The following settings are very confusing IMO:

This is all part of the lens / geometry module. Note that [correct] chromatic aberration is not checked. Despite this, if the two sliders shown are activated, CA correction will be applied!! I had assumed that the "chromatic aberration" checkbox in the module would enable / disable CA corrections for the module. Not so! I apparently had these sliders activated (probably from a preset) when I exported the images shown in my initial bug report.

My primary suggestion / request is that the UI somehow make clear to the user that the two CA sliders in the lens / geometry module are not toggled on / off by the CA checkbox a mere 20 pixels above them. Arguably they don't belong in the lens / geometry module at all if they're not part of the same system. Maybe they would be better in their own module with the standard "power button" to make it clear whether they're active?

My secondary suggestion / request is that something be done to clarify to newer users when / why they should use particular CA modules. It's not even clear how most of them are different from each other, let alone why the user should pick one over another.

[heckflosse]

The following settings are very confusing IMO:

Maybe this screenshot is less confusing. These are different tools.

Why do we need different tools for CA-Correction?

There is auto-ca-correction in the raw-tab which works quite well on bayer files (it's my preferred method) but it also works only on bayer files

As the auto-ca-correction works only on bayer files we need another tool for xtrans files and non-raw files.

If you have a lens-profile which contains data to correct ca, you can use this as well, though never use it together with raw-ca-correction.

Then there is the ca-correction tool below the Distortion Correction tool which you can use if you do not have a lens profile or the lens profile does not contain data to apply ca-correction.

So here my personal preferences:

for bayer files: use auto-ca-correction in raw-tab for xtrans files: use ca-correction from lens profile if available for non-raw files or if no ca-correction is available in lens profile, use ca-correction below distortion correction

[Thanatomanic]

@heckflosse Regardless of your clear explanation: I can really understand the confusion that there three different tools that kind-of do the same thing depending on the situation. I'm thinking what we could do in the GUI to improve this without having to resort to RTFM...

[TechXavAL]

If I have understood it well, it's only a matter of how to tell what each tool does, or most precisely in which kind of situations they have to be used. Perhaps it's just a matter of changing the labels:

• raw files: Raw Chromatic Aberration Correction
• lcp used and has ca-correction: Lens Profile Chromatic Aberration (instead of just Chromatic Aberration)
• when everything else is false (not a raw, and not ca-correction inside lcp): Custom Chromatic Aberration

This last one I've labeled it as custom because maybe there is a reason to use it to fine tune the other ones, or that way it's given the idea that the user have to manually customize the correction.

Just an idea, though

[Thanatomanic]

This last one I've labeled it as custom because maybe there is a reason to use it to fine tune the other ones, or that way it's given the idea that the user have to manually customize the correction.

As far as I know all three methods are applied in very different ways. The raw CA correction works on non-demosaiced data, the LCP correction may apply a higher order correction (see here), and the 'custom' CA correction is a simple radial modifier that shifts the color channels (afaik).

[TechXavAL]

Ok, a new user most probably won't know that, but at least he/she will see that those are different options, not everything the same and with the same name.

What I was trying to tell is that maybe longer labels would be enough to prevent this kind of misunderstandings.

[afontenot]

The following settings are very confusing IMO:

Maybe this screenshot is less confusing. These are different tools.

Actually, I think your screenshot makes the problem even more clear than mine did! They are indeed separate tools, but it's very easy to think that they aren't because they both belong to the same module. Here's the whole thing:

This is how it actually looked just before I discovered the problem. It's actually not even visually clear to me that the manual correction tools are subtools of the lens / geometry module, instead of subtools of profiled lens corrections. But even if it was, the following criticism would stand.

The name of this module is lens / geometry. It's an "always enabled" module, like the demosaicing (for RAW), and that makes sense to me, because even if you want all the lens corrections disabled, these adjustments are always "applicable" to the file, in the same way that demosaic is always applicable, and always first in the toolchain.

My intuition is that CA correction done in the lens module is going to be lens profiled CA correction. That seems to be a mostly correct intuition; the module does contain such a feature. If there are additional sliders in the module, they should be further refinements / adjustments of profiled correction, not a separate feature. In other words, my intuition is that if you have an always on lens module, disabling distortion correction, anti-vignetting, and anti-CA should have the effect of disabling the module. That's not the case: even if you think you've disabled everything, options like this one can remain hidden below a dropdown, and they're always-on, they can't be disabled.

So my suggestions would be the following:

1. Break up the lens / geometry module into the stuff that it makes sense to have always-on, and stuff that it doesn't. We already have crop and resize as individual modules, so make rotation and perspective corrections their own modules too! All these things can go in the Transform toolbox, which currently has only three children.

2. At the very least, move distortion correction, chromatic aberration correction, and vignetting correction to their own modules in the Transform toolbox. These currently give the misleading impression (to me, with 50+ hours of experience with RT) that they are part of the usual approach to lens correction, i.e. a profiled lens, rather than completely separate manual adjustment features. They ought to have the power button on / off toggle so the user can be certain about which features are enabled / disabled without having to open every dropdown in the entire program first.

3. The manual CA correction tool should be entirely missing / disabled if a bayer file is being edited, or if you don't like that approach, some kind of warning should be apparent to the user when trying to enable it.

4. The manual "distortion correction", "chromatic aberration correction", and "vignetting correction" tools should be renamed "manual distortion correction", and so on. This will help clearly distinguish them from the automatic corrections that take place in the lens correction module (created as a result of suggestion 1).

5. Enabling a tool that is incompatible with others should trigger a warning to the user if the tools are incompatible, and in some cases probably shouldn't work at all. For example,

If you have a lens-profile which contains data to correct ca, you can use this as well, though never use it together with raw-ca-correction.

That's what I assumed, but new users might not have that intuition! It would really help RT from a usability standpoint if it was always clear what tool was needed for a particular purpose, which tools were enabled at any given time, and which tools are incompatible with the use of others. These suggestions would help clarify all three with respect to the anti-CA tools.

Summary

I think the Transform toolbox should look like this when editing a raw file:

○ Crop
○ Perspective
○ Resize
○ Rotate
► Lens Correction
○ Manual Chromatic Aberration Correction (disabled)
○ Manual Distortion Correction
○ Manual Vignetting Correction

And warn the user if incompatible tools are in use.

[simohno]

Why do we need different tools for CA-Correction?

There is auto-ca-correction in the raw-tab which works quite well on bayer files (it's my preferred method) but it also works only on bayer files

As the auto-ca-correction works only on bayer files we need another tool for xtrans files and non-raw files.

If you have a lens-profile which contains data to correct ca, you can use this as well, though never use it together with raw-ca-correction.

Then there is the ca-correction tool below the Distortion Correction tool which you can use if you do not have a lens profile or the lens profile does not contain data to apply ca-correction.

So here my personal preferences:

for bayer files: use auto-ca-correction in raw-tab for xtrans files: use ca-correction from lens profile if available for non-raw files or if no ca-correction is available in lens profile, use ca-correction below distortion correction

Thanks for the clarifications, @heckflosse :) I think the notes on incompatibility between the various CA-corr tools should be written in the RawPedia (or have I missed that?). I did not suspect they could conflict and in fact used both before- and after-demosaic CA tools, till now...

So if I have got it right, also from #5719,

• Only the Defringe tool works well with the others
• Lens-specific or generic CA tools (the two in Geometry tab) are not compatible with the RAW CA-correction

Is the manual CA corr (in Geometry tab) usable in addition to the lens-specific one just above?

Your personal preference arises from a better CA removal with the pre-demosaic tool, than with the after-demosaic tool, right?