Episode: 3290
Title: HPR3290: GIMP: More on Layer Tools and Techniques
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr3290/hpr3290.mp3
Transcribed: 2025-10-24 20:16:36

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This is Haka Public Radio Episode 3294 Friday 12th of March 2021
Today's show is entitled Gimp, Moron Leia Tools and Techniques
And in part of the series Gimp, it is hosted by Ahuka and in about 15 minutes long
And Karina Clean Flag. The summer is using some additional tools
for for working with Leia in Gimp.
This episode of HPR is brought to you by archive.org
Support universal access to all knowledge by heading over to archive.org forward slash donate
Music
Hello, this is Ahuka, welcoming you to Hacker Public Radio and another exciting episode
And I am continuing my series on Gimp this time
And this is a tutorial I'm calling Moron Leia Tools and Techniques
And we're going to bring in some things that are very valuable when you're working with Leia's
And as we've said, Leia's are a really important tool in working with these images
So we're going to be spending a lot of time on them
In the last time we did our first example tutorial on layers
First of many, that whenever you open an image such as a photograph
A layer is automatically created to hold that image
Now that is good for a start
But for many things you want to do with an image, you need transparency
And it's not there by default
For example, if I open the image I used to have as my header on my Ahuka.com site
Which we had talked about previously
It was created as a layer in Gimp, but if I erase any of it, what do I get?
Oh, I use the erase tool
And what it does is it replaces it with whatever is my background color in Gimp
Well, that's fine, I guess
The example that I did, it was white because white happened to be the background color
And for a number of the things that you do with particularly when you get to layer masks
It's common to have white as the background and black as the foreground
So, I partially erase the image and okay, now there's white there
But what if my intention was to take the image away so that something else would show through
For that I would need transparency
Now, if you want transparency, how do you get that?
JPEG images do not have transparency by default
So, what you need to do is click on the layer
If you right click on the layer, bring up the properties pop up window
And click on add alpha channel
And that's what gives you transparency, it's your alpha channel that has the transparency
Now, when you erase, you'll get a transparent background
Now, remember that in Gimp, transparency is indicated by a gray scale checkerboard pattern
Which is good because you know what you're working with
But when you export the image, it will be truly transparent
Now, note that you only need to add an alpha channel
In the case of a layer created automatically in Gimp when you open an image
And for some images, there may already be one
PNG images have an alpha channel
But JPEG images don't
So, any time you create a new layer by using the create new layer button in Gimp as opposed to opening an image
It's created with an alpha channel by default
So, it's just something you need to know
If you forget it, one day you'll be working on something and say, wait a minute
Why am I not getting any transparency when I erase this part of the image?
Oh, gotta add that alpha channel
So, good thing to know
Now, we want to talk about layer groups and layer linking
Which are kind of related in a way
There are ways of letting you work with a bunch of layers as if it was a single unit
And that can be a very convenient thing to do
Because you can create
I've watched people do examples of things in Gimp where they would create a layer group with six or eight different layers in it
And copy that layer group and duplicate it
You know, a Gimp Pro is going to start doing stuff like that
Now, there are two ways, you know, layer groups, layer linking, layer groups
First appeared in Gimp 2.8
And they make it easy to create a permanent
I put permanent in quotation marks a little bit
And nothing is permanent, you could undo the layer group
But generally, if you create a layer group, it's because you want these things to be always linked together
And the main point in creating one is you want to do certain things like transforms
And you would want it to affect all layers equally
Now, a good example is rescaling or resizing an image
If you have layers in a layer group, you can resize all of them equally by rescaling the group
Instead of fiddling with each individual layer, which is a pain in the butt
Now, to create a layer group, you need to have an image open
And therefore, at least one layer open
Then just go to the second icon on the bottom of the layer's dialog
Next to the create new layer button
The second button is the create a new layer group button
And it looks like a folder with a plus sign
This will create what looks like a new layer in the dialog with the default name layer group
Now, you should change this to something that makes sense for your project
For example, in our previous example project, I had six images representing office software
And making them a group with a name like office software images would make sense
To do this, right-click on the group layer and go to edit layer attributes in the pop-up
Now, I can do the same thing with my text layers and create a text group
Now, once your group is created, you can just drag layers into it
When you do this, the layers inside the group are now indented
And an arrowhead is added to the group layer that can expand or hide the layers
Now, you can hide individual layers by clicking the arrowhead to close them up
And then you'll only see the layer group itself and not all of the components
But then if you need to get to individual layers inside it, just click the drop down and open it up again
Now, if you had carefully arranged a bunch of images in a collage for instance
In a layer group, with the images in the order you want them in the stack
Now, let's you move the whole group around without disturbing your arrangement
And if you look closely, it is a little hard to see
The thumbnail image of the layer group will now display the resulting image from all of your layers as you have arranged them
Now, I did an example on my website of this
And, you know, there's links in the show notes and folks you should always check my show notes for all of these episodes
And now, I blew up the image to make it hopefully a little bit easier to see that the layer group thumbnail is now the composite result of everything that's in the layer group
Now, the other thing you can do to make it easier to see your layer thumbnail is to click on the arrowhead on the top right of the layer's dialog
Called configure this tab and in the pop-up this opens
Go to the preview size and select the larger size
This will require that the entire layer size in the layer dialog also gets larger
And if you have a lot of layers that can mean not seeing everything at once, so there's a trade-off, but you do have options here
Note that you add layers to a group at any time, remove layers at any time, just by dragging them, it's all drag and drop
Now, as an example of what you can do with layers in a layer group, I selected my text group, then turned off the visibility for my images group and then used the perspective transform tool on the cux group itself, not on the individual layers
And I got a nice effect from doing that, and that just illustrates one of the many conveniences of using layer groups
Of course, you can move groups around as a unit, rescale them, and so on
Now, the other way to operate on multiple layers at once is something called layer linking
And I think of this as something less permanent in how I use it, I can link any two layers at any time
And the way to do this is to just click to the right of the eye icon on the layers you want to link and you'll see the image of a chain link
Any layers you do this to are linked for the moment, but you can unlink them at any time by clicking the chain link icon to make it go away
You can then use transform tools, for instance, on the linked layers
What will happen is that you will see the transform happen on the selected layer as you work, and when you then commit the change, you will see the linked layers respond as well
So I did an example using that header image that we created, and starting with the images it was before doing any transform
I then clicked the image of the woman doing the presentation and the office word cloud and linked them
And then because I linked them, I could then rescale them, and they would both rescale equivalently
Now you can see the handles for the rescaling when I'm working on it because I haven't committed it yet
When I do commit it by pressing the scale button on the scale dialog, both images are now changed
Okay, this worked fine as it is, but what if you want to see your changes on all of the images before you commit so that you can fine tune everything
A good way to do that is to use an option in the layer menu called new from visible
To use this trick, first turn off visibility for all of the layers other than the linked layers
Note, if you're working on layers linked in a group, you also need to turn on visibility for the group, but all non-linked layers in the group will need visibility turned off for this to work
Then go to the layer menu, select new from visible, this will create a new layer called visible
Then when you apply your transform, you can see how it affects all of the linked layers before you commit
And I have examples of this on my webpage
Now you can see in this image the handles of the rescale tool showing that we have not yet committed the rescaling, but we see both layers resized together
Once we're happy with the result, press the scale button to commit the changes, then delete the visible layer which you no longer need
Now, I keep talking about committing
This is an impermanent form of commitment in the sense that if you've done what I've suggested and have increased the number of undo levels in Gimp, you just press control Z a few times and get, you know, remove all of the things that you've done
Or maybe you were really careful and created a duplicate layer group and worked on that, so you still have the original
And you can go back to that at any point
Now opacity, so far we've treated all of our layers as being either completely over or completely under other layers
And thus the images are covered by anything in a higher layer, but this does not need to be the case
To illustrate what I mean, I'm going back to our old friend Wikipedia Public Domain Image Resources page to find some images
I'm looking for photos this time, so I went to a site called Imageric and I found a few
One is a family photo of four women and another is a photo of a rose picture
And I check for the license, everything on the site says it is licensed as CC0 that's Creative Commons equivalent of Public Domain, so that's a good one to use
Now I opened up both of these images in Gimp using the Open as Layers option in the File menu, this gives me two layers
I put the layer with the four women on top and then reduce the opacity to 70%
This gave me an image where I could see the roses coming through the image of the women
Now, another thing you could do with this is use a pattern or a color layer
For example, I did an image of the women with a 50% opacity yellow green color layer
And then I did another one with a 50% opacity using a paper pattern on a layer
So you can see there's lots of possibilities from manipulating the opacity of layers
There's still more to discuss on layers, so we're going to go on with this
And we haven't even gotten to modes, and we won't for a while because there's so much good stuff to do here
So, this is a hookah for Hacker Public Radio signing off and is always encouraging you to support FreeSoftware
Bye-bye
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