Participant

Question

LUMINACE MASK

Forum|Forum|8 years ago
January 1, 2018
4 replies
1001 views

When I like make a luminance mask, I can go to the RGB channel and click on it.

A selection is made and all changes should take place only on the selected area.

Instead, the changes take place over the whole image.

If I create a selection with another tool, for example fast mask, everything works perfectly.

I tried using luminance masks on another computer and everything goes perfectly.

I don't know why but I would be very happy if I could solve the problem.

This topic has been closed for replies.

fabrizio211945Author

Participant

Unfortunately I am Italian and I do not know English well.
Once you open a photo in Photoshop, going to the Channels panel and clicking on the RGB Channel, all areas of the photo with a brightness above 50% are highlighted, with the classic moving ants that delimit the selection. This is a first selection from which we can obtain other selections with less bright areas.The selection obviously serves to be able to operate with modifications exclusively on the selected area.This is what I did until two or three months ago.
Now the changes do not take place only on the selected area but on the whole image. I do not know why. Maybe I didn't say it clear enough. I don't want to know how to create luminance masks, I want to know what happened because I can't make them work anymore.

D Fosse

Community Expert

We need to get this out of the way before we can move on here:

the classic moving ants that delimit the selection

We need to be very clear on this: it is not delimiting the selection. It is not fully selected inside the marching ants, and fully unselected outside. The marching ants is a 50% indication, this is the boundary where the pixels are 50% selected. Halfway selected and unselected.

If I ctrl-click the RGB channel on an image I get this:

But the actual selection looks like this - light is more selected, dark is less selected:

If we can agree on this, but this is not how it works for you - then we can move on to figuring out why.

fabrizio211945Author

Participant

Why? That's what I'd like to know ....

Norman Sanders

Legend

As an alternate approach I have found a Luminosity Layer to be helpful, particularly in images such as the one shown here. The method:

1. Add a duplicate layer

2. Choose Image > Apply image … Channel: Green is usually best. Blending: Normal

3. Change Layer blending mode from Normal to Luminosity

5. Image > Adjustment Curves.

6. First mark and then bend the curve to increase contrast in the flesh tones. Don’t fret if you later realize you overdid it a bit, as I see now. That can be adjusted with the Opacity slider.)

D Fosse

Community Expert

Yes, luminosity is an incredibly useful concept. I use luminosity layers and luminosity masks all the time, to the point where I suspect it's my most frequently used tool.

It's worth noting that luminosity is not the same thing as RGB brightness. Luminosity is basically the L channel in Lab. The reason it's so easily available in RGB, is that Lab is used as Profile Connection Space in color management operations, so there is always a set of Lab numbers "in the background", whatever color space or color model you're working in. Any color or tone always has a Lab reference.

What distinguishes luminosity (as opposed to brightness), is that it's entirely separate from any color components. This means that any color's inherent lightness is taken into consideration. A bright yellow is light, but a deep blue is dark. They don't have the same luminosity. In the RGB model they will be treated the same way and have the same brightness.

I see you finally got your true avatar up, Norman, it was about time!

Norman Sanders

Legend

Dag, just a carryover from my previous life in the CMYK world. My first choice was Magenta but it was always too heavy. Lightness channel was usually too thin. And G seemed just right (sounds like the three bears and porridge thing) so I settled on Green -- always with Color Sampler & Curves and often with the Opacity slider. It is quite flexible.

And thanks for the Lab Man avatar thumbs-up. I owe that terrific job to Trevor.

D Fosse

Community Expert

Don't be fooled by the "marching ants" marquee. That's just the 50% boundary. A selection isn't necessarily either/or, it can be gradual.

The whole point of a luminance mask is that white is fully selected, then gradually less selected down to full black, which is not selected at all. So anything you do in that selection works on the whole image, but with a light/dark gradient.

c.pfaffenbichler

Community Expert

I can go to the RGB channel and click on it.

Do you mean cmd-click?

A selection is made and all changes should take place only on the selected area.

What changes?

Don’t you use Layer Masks?

Please post screenshots (including the pertinent Panels) to illustrate your problem.

fabrizio211945Author

Participant

If I make changes, with curves, for example, changes must only take place on the selected area. Instead in my computer the changes happen on the whole area and therefore the mask is useless.

c.pfaffenbichler

Community Expert

therefore the mask is useless.

What is the Selection/Layer Mask exactly?

Please post meaningful screenshots that include all pertinent Panels (Layers, Channels, …).

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