Hi,

The "Auto" button on the Levels dialog has a fixed behaviour today (which I don't know exactly which is).

Its behaviour should be configurable by the user. Here are two possible behaviours that should be available (maybe there are more, I'm not sure):

- choose the exact darker and lighter pixels as the black and white point targets respectively
- choose the darker and lighter pixel for the black and white point targets after discarding a configurable percentage of the darker and lighter pixels first. I.e., to choose the black point target, first discard the x % darker pixels and them choose the darker pixel on the remaining ones. x here would be a configurable parameter. The same process would be used for the white point target. The configurable value of discarded pixels for black and white point target automatic selection should be independent of one another.

The first behaviour can probably be considered an special case of the second where the configurable percentage of discarded pixels for both black and white points is set to zero.

The user interface for this functionality could be accessed by the user double clicking the "Auto" button.

Regards,

Rodrigo Severo

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Liam,

First of all, thanks for your time and input on this matter.

On Mon, Jun 15, 2015 at 2:10 PM, Liam R. E. Quin wrote:

On Sun, 2015-06-14 at 19:05 -0300, Rodrigo Severo wrote:

Hi,

The "Auto" button on the Levels dialog has a fixed behaviour today (which I don't know exactly which is).

The source code is available -- essentially it stretches contrast in each R, G, B channel separately. If you press Auto and then open as curves, you can see. The end points are, however, a few percent in from the ends, limiting its usefulness in a professional setting.

So you agree that the behaviour of the "Auto" button should be at least changed, if not configurable ;)

Its behaviour should be configurable by the user.

The point of it is that it "just works". An auto button should not be configured.

Why not? It certainly should have a reasonable default but why not be configurable?

The "Auto" here refers to automatically choosing the black, white (and grey?) points. This wouldn't be changed at all.

The configuration would allow the user to choose another way to for Gimp to choose these points. But they would still be chose automatically

I think really what you are asking for is a "stretch contrast" filter that has configurable black and white points.

That would be the poor version of my idea.

If we have configurable black and white points on Levels (and hopefully in Curves also) the auto setting could be the first step on a much more refined Levels or Curves setting.

Note that you can already configure the black and white points in levels using the eye dropper.

I know how to manually choose the black and white points. But is there a way to configure the way Gimp automatically chooses them for me?

The user interface for this functionality could be accessed by the

user double clicking the "Auto" button.

That would be a "no" :-) There aren't any other buttons that behave differently when you double-click on them (and actually for good reason, as no-one would ever guess it, and because it would mean every button would have to wait to see whether the user double-clicked before doing anything, giving a UI feeling of slowness.

I think you might be right. Do you have another suggestion on how to access configurable values for these buttons? If this were to be implemented, I believe these configurations should be accessible straight from the Levels dialog.

I'm supportive of being able to set the levels/auto clipping percentage, perhaps in the Colours/Map/Stretch Contrast GEGL filter.

I think this is a good idea. I just think that not having this kind of configuration also on the Levels dialog stiffens Gimp interface unnecessarily.

What do you think?

Regards,

Rodrigo Severo