Mask post-processing - Tone curve

Hi, I try to understand how and when to use the Tone curve option in the module Mask post-processing.

When I use the standard tone curve there and reverse it (left up, right down), the mask is inverted. But why would I want to invert the mask at this place, instead of using the Inverted option next to Show mask?

Setting Tone curve back to standard and changing the curve, I see that the mask is changing without that I can tell “if I do this, the mask changes like that”. So what is a good use of the tone curve here?

Btw. The graph jumps out of its window with some settings.


This comes from the curve type. I prefer control cage in most cases

@agriggio should tell you about ART specifics with regard to the mask, but I just put a similar set of control points in rawproc’s curve and it did the same thing…

A control-point curve is one of those “sharp knife” tools, there are ways to use it that can hurt you. All the spline algorithm is trying to do is to make a smooth curve from the slope of the center point to the slope of the right point. it goes out of bound because you made it do so…

Also, the negative slope of the right-hand side is not good unless you’re looking for an abstract rendition. Generally, negative slope in a tone curve is bad. Flat or near-flat slope isn’t great, although I’ll let it go if I’m trying to aggressively change something in the low end and keep the high-end linear, if the flat area corresponds to a place in the image with little data.

Just some food for thought…

Okay thanks, now I understand it’s the curve type that provokes this behavior.

As said in my first post, I just tried to find out how this tone curve works on a mask, that’s why I was playing with the curves. And I still don’t have a clear idea what’s going on there, but perhaps Alberto can shed some light.

Thanks anyway for your reactions.

the tone curve is just a function on the mask pixel values: for each pixel in the mask, which is a value in [0,1], the output is the application of the function defined by the tone curve to that pixel (again a value in [0,1]). Of course, if there are harsh transitions in a mask (e.g. one defined by a brush with no smoothness or feathering), then you will not see much effect (if any) when applying the curve, because all the pixels will be either 0 or 1. But if you have a mask with gradients, then playing with the curve will alter it.
Anyway, it’s meant as a fine-tuning option, and it’s perfectly ok if you don’t see the need for it.


I forgot to say that I was playing with a gradient mask indeed, and changing the tone curve can have quite dramatic effects.

Okay, thanks. I still think the tone curve can be of use, I’ll investigate some more to understand the “if I do this then the image changes like that”, because one can produce some interesting and at times amazing effects ! :slight_smile:

I have not used masking much in ART…more DT but I thought it was like the contrast setting in DT which can really assist to sharpen the edge of the mask???

Well, for me it’s one of the great parts of Art, very effective and very easy to use. But I think this tone curve found under Mask post-processing is not for edge-sharpening the mask (and useless with a gradient mask of course!).