Hi guys,

Over the weekend I went back and re-visited the creation of luminosity masks based on Tony Kuypers original tutorial for Ps. This time I wanted to create the masks in the same method as Tony, but strictly by using GIMP channels instead.

I documented what I did as a quick tutorial, and wrote up some script-fu to automate it:

Getting Around in GIMP - Luminosity Masks Revisited

I am 100% certain that the script-fu could be made faster/more efficient, so if anyone wants to hack at it, please do!

As always, comments/suggestions/rants welcome...

The results on your blog are stunning. Thank you for the tutorial and the script. I'll give it a go in a bit.

Thanks! I hope you'll be able to get some use out of the process.

Nice one, very informative tutorial.

Another good one... The efficiency nazi in me wondered why you didn't get the Dark from the Light by duplicating it and then applying Color/Invert. But then using the same technique for all masks makes the tutorial easier to follow.

Yeah, once you start subtracting the light channel, it's easier to keep going rather than explaining how to reselect a channel a few more times as you build out each level of masks. I thought this way made the process a bit easer to follow...

There's really not much to be done to improve the speed, as all the heavy lifting is performed by the core libgimp functions. Nonetheless, there are a couple of other improvements that could be made, and so I provide the following revised version of your script:

http://chiselapp.com/user/saulgoode/rep ... 99c37cda66

Here is a list of the changes incorporated:

• The original contents of the paste buffer are preserved (scripts should not interfere with copy-paste operations, unless the purpose of the script is to generate a particular paste buffer).
• Script will work with layers that do not fill the entire canvas.
• Script now honors the selection, i.e., it will only generate its masks within the selected region.
• Script can be run multiple times; either for different layers or for different selected regions.
• Mask names have the original layer name appended to them (if multiple runs are made on the same layer, mask sets will also have #1, #2, #3, ... added).
• Script will work with grayscale images.

EDIT: The following paragraph is no longer valid. The above link is to a version of the script that follows Pat David's approach to the midtone masks.
I also swapped the M and MMM masks to provide better consistency with the light and dark masks (that is to say, the M mask is now the most inclusive of the midtones, while the MMM mask is the least inclusive). This is opposite from the original script (and perhaps from Mr Kuyper's Photoshop actions?).

Check out your Channels dock ("Windows->Dockable Dialogs->Channels").

You will want to read Mr David's tutorial to understand how all of the new channels can be used as luminosity masks.

Oops. You are right. There is no dialogue, and therefore the command should not have had an ellipsis after it. (I have updated the script.)

Thank you, I will try it again.

I replaced the script and it still has no dialogue. I will go find Mr. David's instrucs.
This is what shows in channels.

The script does not pop up a dialogue and it does not change the layer in any way. What it does is create a bunch of channels that can be used as selections or layermasks when you are editing the image. I have added a screenshot to my previous post that will hopefully illustrate things better.

Hmmm. It appears that you had the transparent (BG) layer active when you ran the script. You should have the layer with the lady's face active.

nothing changed on the layer.

Correct. The script does not modify the layer. It only creates the masks for later usage.

o, okay that explains it, I just wondered why there was no dialogue. Thanks Saul.

I was kind of hoping I could get Saul to eyeball this thing for me
I had been using for a while your previous script for generating this same thing (from meetthegimp: http://forum.meetthegimp.org/index.php?topic=1196.0). (Thank you for that, btw).

The problem was that in your version there, the mid-tone mask was full-range (similar to the change you've made here if I read your previous post right).

I was just wanting to keep parity with the nomenclature and workflow from Tony's original Ps tutorial for those who may be coming over. (Also, part of the intention was to help users new to using channels like this to mentally make the connection that wide lights - wide darks = narrow mids, etc...).
[edit]
Also, if a user wanted to separate out a single first range of luminosity, they might make 3 layer copies, and apply L, M, and D to each of those. They would likely expect that changes to each of those would be associated with the appropriate range, but if you flip M/MMM then the MMM will overpower the L and D by quite a bit due to it's width (Hope I'm being clear).
[/edit]

Either way, I'm glad you had a look at it, because my script-fu, frankly, sucks. I'm going to update the tutorial post with a link to your post here. Thank you very much!

Here is a version of the script that employs your M-MM-MMM order.

http://chiselapp.com/user/saulgoode/rep ... dd4d931473

You, sir, are awesome! Thank you for that! I'm going to add links to this thread on the post (and over on the registry as well).

Interesting tutorial i like the idea and the result but i am fascinated also by possible variations :

as derive some of the masks not from the composite but from a single channel ;

as example a black & white panorama derived from only the red channel of a RGB image usually will show a much more dark and dramatic sky and make the skin of a face more pale but also ,often younger .

Obviously for layermask effect will be different , yet should be possible use to control luminosity not only globally but even differently on the main color ranges ,i.e. to dose luminosity differently for sky, skin and greenery .

just wandering ...