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Trouble following the luminosity mask tutorial. - Printable Version

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Trouble following the luminosity mask tutorial. - kirbywan - 04-15-2018

So I 'm a complete beginner. I just went through all the basic tutorials except the assets folder. I tried to go through the Luminosity mask tutorial, but I'm getting stuck at the "Create Even Darker Masks" section. I don't get results similar to what the tutorial has. When I subtract the lights channel (L) from the darks channel (D) I get something that looks less dark. I think I'm missing a few key steps that would probably be obvious to a more experienced user. I could provide my file for comparison if you want.

Thanks all,

-Kirby


RE: Trouble following the luminosity mask tutorial. - rich2005 - 04-15-2018

Is it this tutorial? https://patdavid.net/2013/11/getting-around-in-gimp-luminosity-masks.html

It is good to know how it works but there is a script to generate all the channels. You can use it to compare with your results.

However my guess. Are you successively subtracting the L channel selection from the previous or something else.

This is the L channel - from one of the RGB desaturated, and the D is the whole image selected minus the L selection. screenshot https://i.imgur.com/3eZ9RoL.jpg

Subtract again from the last resulting selection gives a DD channel. https://i.imgur.com/QajQEPd.jpg

Pat David can be located on the pixls forum https://discuss.pixls.us/ you could always ask the question there.


RE: Trouble following the luminosity mask tutorial. - kirbywan - 04-15-2018

That looks like the same tutorial. But I was following the one from the gimp homepage here: https://www.gimp.org/tutorials/Luminosity_Masks/

Let me go through that and see if it answers my question. I'm not interested in a script as I'm trying to learn how to use it. I'll see if your explanation and pictures help, or I'll ask a more detailed question.

Thanks for your response.

-Kirby

So that's the identical tutorial, at least up to the point I'm failing. I'm going to give as detailed a walk through as I can to see if someone can spot my misunderstanding. I have dragged the red channel down and named it 'L'. At this point:

I select the image, (in image frame rmb -> select -> all) get the marching ants.

On 'L' channel I subtract the image (on 'L' rmb -> subtract from selection) Can now see the marching ants and diagonal bars marching.

Save as a new channel and rename (in image frame rmb -> select -> save to channel) which creates a new channel that I can rename 'D'. Still see the marching ants and diagonal bars.

Up to this point I feel like I'm good. Now let me create the DD channel:

To make sure I'm starting from the same point, I cancel the selection (rmb -> select -> none) no marching ants.

With the 'L' channel selected (note that none of these have the white boarder indicating that the selection is active like on the 'Layers' frame.) I select the image, (in image frame rmb -> select -> all) get the marching ants.

On 'D' channel I subtract the image (on 'D' rmb -> subtract from selection) Can now see the marching ants and diagonal bars marching.

Save as a new channel and rename (in image frame rmb -> select -> save to channel) which creates a new channel that I rename 'DD'. Still see the marching ants and diagonal bars.

I cancel the selection (rmb -> select -> none) no marching ants.

But now I look and the 'DD' Channel looks almost like the 'L' channel, not darker then the 'D' Channel.

https://i.imgur.com/81XA1Rh.png

If I repeat the process only subtracting from the 'DD' channel, to get a 'DDD' Channel, it looks dark, but about the same as the 'D' channel.

https://i.imgur.com/djxbAoP.png

Thanks for your help.

-Kirby