Episode: 3420
Title: HPR3420: Normal Layer Modes: Erase, Merge, and Split
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr3420/hpr3420.mp3
Transcribed: 2025-10-24 23:05:24

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This is Hacker Public Radio Episode 3424 Friday, 10th of September 2021.
Tid's show is entitled, Normal Layer Modes, Erase Merge, and Split in his part of the series
Gimp It Is Hosted by Auga and is about 10 minutes long and carries a clean flag.
The summary is, we continue our look at the layer modes in Gimp.
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Hello, this is Auga for Hacker Public Radio and inviting you to enjoy another
exciting episode in our ongoing series on Gimp and I'm going to look at a few more layer modes here.
This is in the section of Normal Layer Modes, which is the first of the sections for layer modes.
This episode might be a little bit shorter because I could not get enough information on all of these,
but I want to present what I can before moving on to the next section.
Now, there are three remaining layer modes in the Normal section, what are called Normal Layer Modes.
Those are Erase, Merge, and Split. Erase will erase from the bottom layer any pixel
for which there is a pixel in the top layer.
So, if the two layers are the same size, using Erase Mode on the top layer would simply make
the bottom layer completely transparent by erasing all of the pixels.
To be of any use, I would think you would need to have the top layer contain some kind of shape
on a transparent background. Then using the Erase Mode would invert that on the bottom layer.
Where the opaque shape would become transparent. This would create something interesting,
although anything I've been able to think of could be done in other ways and probably more simply,
but still, there are some interesting effects to be had here. So,
I need to illustrate this process. So, I started by deciding to add a new font. We haven't done that
for the last few episodes. So, I went to Font Library, which has lots of open font licensed texts.
Again, links in the show notes for all of these things.
And this is one of the places discussed in our episodes on Free Public Domain and Creative
Commons assets. Now, this license is considered free by the Free Software Foundation,
which is a pretty good credential. So, when I go looking for fonts, I look for
OFL, open font licensed. OFL licensed fonts by preference. Now, I can use them anywhere without
worrying about royalty issues. In fact, I got an inquiry the other day from someone who saw one
of my articles. Remember, when I do these things, I always write it up first on my website before
I record track or public radio. And this person said, hey, I saw your article and this
happened to be about photography, open photos, and said, how about including the photos from our
website. And I went and I looked and I said, you're not using public domain or CCZero licensing.
I'm sorry, I am not going to include you. You know, maybe I was being unfair.
I mean, the license looked good, but I just, you know, someone's going to write their own license
and then say, well, this is just as good as all the others. Now, you know, we solve that problem.
I'm just not going to do it. So, anyway, back to the story. I went looking for something in the
DingBats section and found a font called fivefold ornaments, et cetera, which had some interesting symbols.
So, I downloaded the zip file containing the font. I moved it to my dot fonts directory
and in under my home, so it told us slash dot fonts. And that makes it available to any
application on my Kabuntu box, which is why I want to do it that way. Then I click the fonts tab
on the upper right where you see your tabs for brushes, patterns, gradients, and so on.
And it just, you know, clicked on any font at random and then selected re-scammed font list.
Now, this made my new font a selection, so I clicked on it to select it.
Then I created a new layer filled with transparency, selected my text tool,
and drew a text box and typed some letters, A, B, C, D, E, which showed up as symbols.
I then moved the borders of the text box to just touch the symbols
and centered the box using the alignment tools. So you can go to the Tools menu,
Transform, Tools, and then Align, or you can click on the Move tool and select Alignment.
Either one will get you where you want to go. And I got a result of five circular,
swirly symbols. Okay, that was nice. So then with this as the top layer, I selected a race mode,
and the bottom layer is still the toy image. And it erased, where those symbols were,
was now erased from the picture. And it was transparent. Okay. Now, I thought maybe I can put
something under the toy image layer that would show through now that I've got some transparency.
So I decided to do this with a gradient and picked full saturation spectrum CW, which is one of
the gradient options. I created a new layer and used the gradient tool to fill it and moved it
to the bottom beneath the toy image layer. Now, at first this had no effect. But I created a layer
group and moved the toy image and the text layer with the symbols into this new group. And then
under the layer group put my gradient layer and everything worked. So now I've got my five symbols
with a color gradient going across them. Looks rather interesting.
And you know, if you want to see the images, you know, link in the show notes to the page of my
website where you can see the images that I created. Now, another interesting feature is that
this can reverse a layer mask effect. Now, recall that layer masks work by creating transparency,
and so does layer mode. And it can be like a double negative. To see how this works,
select the top layer and add a layer mask using the button on the bottom of the layers window.
Make sure you select white, which is full opacity. And do not leave a check mark in the invert mask
box. Then make your foreground color white and select the paintbrush tool.
In normal layer mask situations, painting the layer mask with white would make the layer opaque,
thus hiding anything underneath it. But with layer mode set to erase, painting with the white color
actually makes the top layer transparent where you paint and reveals the layer below it.
Okay. So that's great. We understand erase mode now. What about merge and split? These are
obviously opposites in some sense, but there is no documentation of them right now.
And I have not succeeded in working out what is going on with them.
I did work it out for color erase and erase, which also have no documentation. But with my
experimentation, I was able to work out what's going on. Can't with merge and split. If someone
knows how these work please let me know. I did find a video on YouTube from Michael Davies.
It kind of touched on it briefly, but I could not replicate what he did. And there's got to be
some trick that I'm missing, but you know, that's what it is. I can't find anything in the Gimp
Forum. And again, there's a link in the show notes if you want to know about the Gimp Forum.
This may happen again with undocumented layer modes, since there are more of them ahead.
When I can work it out through experimentation, I will explain what I discover.
When I can't skip it and move on. Bear in mind the documentation is important,
but it is usually the least desirable, desirable job on any project.
I learned this as a project manager. When documenting what the project did was like pulling teeth.
And then the agile practice came along and made it sound like not documenting anything was a virtue.
My personal view is you should document like the person who will have to take your place
is a homicidal maniac who has your home address. And I practice what I preach.
When I was working on projects at St. Joseph Mercy Hospital, I got rave reviews from the IT staff
who had to support the systems I installed because they knew I would document them carefully and
completely. So this is a somewhat shorter tutorial than usual, because I would rather start fresh
on the next group of layer modes, which is the light and only group. So for now, this is Ahuka
for Hacker Public Radio, signing off and encouraging you as always to support free software. Bye bye.
You've been listening to Hacker Public Radio at Hacker Public Radio.
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Today's show, like all our shows, was contributed by an HPR listener like yourself.
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Hacker Public Radio was founded by the Digital Dog Pound and the Infonomicon Computer Club,
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please email the host directly, leave a comment on the website or record a follow-up episode yourself,
unless otherwise stated. Today's show is released under Creative Commons,
Attribution, ShareLite, 3.0 license.
You've been listening to Hacker Public Radio at Hacker Public Radio.
We are a community podcast network that releases shows every weekday, Monday through Friday.
Today's show, like all our shows, was contributed by an HPR listener like yourself.
If you ever thought of recording a podcast, then click on our contributing to find out how easy it really is.
Hacker Public Radio was founded by the Digital Dog Pound and the Infonomicon Computer Club,
and is part of the binary revolution at binrev.com.
If you have comments on today's show, please email the host directly,
leave a comment on the website or record a follow-up episode yourself,
unless otherwise stated. Today's show is released under Creative Commons,
Attribution, ShareLite, 3.0 license.
