Episode: 3125
Title: HPR3125: GIMP: The Canvas
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr3125/hpr3125.mp3
Transcribed: 2025-10-24 17:18:16

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This is Hacker Public Radio Episode 3125 for Friday 24 July 2020. Today's show is entitled,
Gimp, The Canvas. It is hosted by Ahuka and is about 13 minutes long and carries a clean flag.
The summary is, The Canvas is the first key concept in learning 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.
Hello, this is Ahuka, welcoming you to Hacker Public Radio and another exciting episode
in my new series on The Gimp. And what I want to do today is take a look at something called
The Canvas. Sort of a place where everything starts and ends. The Canvas is where all of the work
in Gimp takes place. It is in the center of the screen when you open it up and there's tools next
to it on the left and then next to it on the right are layers and brushes, etc. So your screen
basically divides into those three sections, you know, toolbar, canvas in the middle,
layer and brush bar on the right. Now if you're working with an existing photo or image,
that will determine what your canvas is in most cases unless you open the image in a layer which
we'll talk about in a little bit. But if you are creating something from scratch, your first
decision will be to choose the size of the canvas. To start a new canvas, go to file new and you'll
see a window for setting up your canvas. And it's immediately going to ask you some things like,
well, what kind of image size do you want to have? That's your most basic kind of question here.
There are some templates that will help you with that. So they include some common screen sizes,
like 640 by 480, document sizes, like A4, which is the standard letter size in Europe and so on.
Templates can save you time since they combine a number of settings into one template, but you don't
have to use templates. You can kind of roll your own if you want. There's also an advanced options drop
down. You click that, it opens up and you can set resolutions. So x and y resolution pixels per inch,
color space, whether it's going to be RGB, red, green, blue, color, or grayscale.
And if you're going to be printing something like on a standard black and white printer,
there's really no benefit to using RGB color. You might as well just go with grayscale.
The thing I want to focus on here is the resolution, which is defined by pixels per inch,
or pixels per centimeter, per pica, per point, and so on. Note that it is a drop down.
It helps if you know where the image will be used. You might make different choices if this is
for print than you would for a web graphic. But there is one other thing about resolution worth
commenting on. Images can be resized when you are working with them. And if you start with a small
image and later decide to make it larger, the image will get more fuzzy because the number of
pixels or points is fixed. So an image that is sharpened clear of a small size will not look
that good when the size is increased. But if you start with a larger image and later shrink it,
you can get better results. Now this is one of the key distinctions between raster-based and vector-based
graphics. Vector-based graphics use equations such as bezier curves to define the image
and can be resized to any scale without any loss of clarity.
For that reason, a graphic that you want to use in a number of sizes with some flexibility
should be done in a vector-based format. A good example of that might be a logo.
You might want to print that on stationary, on envelopes, in various sizes,
use as a web graphic, place on a banner, and so on. If you started with a raster-based
graphic, you will not be happy with the result. As we mentioned last time, an open-source vector-based
graphics program is in Inkscape, so check it out. Inkscape is a wonderful program, I recommend it
highly, but this is about the Gimp. Photos are made up of pixels and are raster-based objects,
so a raster-based editing program like Gimp is perfect if you're going to be working with photos.
And that's one of my main use cases. I decided to do this dive into the Gimp because I wanted to be
able to fix a bunch of old photos. I got photos that were taken 40 or 50 years ago
that I would like to take a look at. Well, I've taken a look at them, they don't look that good.
If I can fix them, that would be nice. Anyway, back to the resolution thing. When you set up the canvas,
you pick your resolution, you pick the size of your images. This is like if you were a painter,
one of the first decisions you would make before beginning a new painting is to choose the size of
the canvas. So doing this in Gimp is not so odd. The advantage of doing it in software is that
you can make changes later. If you're a painter, you can't be halfway through a painting and say,
I just want a bigger canvas. It's not that easy. But if you want to change the size of your canvas
in Gimp, you just go to the menu bar up top and you find the image menu. And when you click on the
image menu, you see a thing that says canvas size. That's going to let you revisit some of the choices
you made earlier. Now, a note about photos. If you do not create a canvas first, but simply open a
photo by going to file open, you will open the photo on a canvas that is the size of the photo.
But the photo in the canvas are still two separate objects. If you resize the canvas by going to
image canvas size and then increasing the width, you'll see a space on the side that represents the
blank canvas expansion. Click the resize button and you'll be looking at this added space as a
gray checkerboard pattern. Now, go back and add some vertical space in a similar manner and you will
see added canvas at the bottom with your original photo in the upper left corner.
If you cannot see the whole canvas at this point, you can zoom out by going to view zoom
or do what I do and this works in most programs. Hold down the control key and use the scroll wheel on
my mouse. Now, you can experiment a little with this by using the move tool, tools transform move,
which lets you use your cursor to click and drag the photo or there is a keyboard shortcut,
which is the letter M. So you just press the letter M and your cursor will suddenly be the move tool.
But I mentioned the menu just because there's with so many different keyboard shortcuts,
I can't always remember them all. What was the keyboard shortcut for such and such?
So it helps if you know that there's a logical place to look. The tools menu is going to tell you
about that. Anyway, once you've got it in the move tool, you can drag the photo off to one side and
when you do part of the image that is not within the canvas will disappear. Now, you haven't lost it
because you can always just drag it back onto the canvas. You can move the photo around the canvas
with the move tool and that is fine. But suppose you want to be a bit more precise.
Well, we can go back to image, the image menu and this time select fit canvas to layers.
This will bring the canvas back to the size of the photo and get rid of that extra space.
Now return to image canvas size and this time add space to the canvas as needed.
But then before you accept the resize, take a look below the width and height boxes.
The offset boxes let you specify the position down to the pixel.
The x offset is how far from the left side the photo will be
and the y offset is how far from the top edge the photo will be.
Now, if you used to graphing coordinates, the y offset would be the opposite of what you expect.
But there it is. When you're graphing, you count the y dimension going up from the bottom,
here with the offset you're counting it going down from the top.
Now, if you simply want the photo centered, don't bother with setting any offsets,
just click the button for center and it will be centered both vertically and horizontally.
Now, if you had originally created a canvas size smaller than the photo and then opened the photo,
one of two things will happen depending on how you do it.
If you simply use open, the photo will open and the canvas will increase to match the photo.
But if you use open as layers, you will only see a portion of your photo.
It is, in essence, cropped to fit the canvas size.
But the whole photo is still there. If you use the move tool to click and drag,
you can bring different portions of the photo onto the canvas where it will be visible.
An alternative way to accomplish this is to make a selection using the selection tool
to top of the tool's sidebar on the left. You have three selection tools,
rectangular, oval, and freeform. But for now, let's just use the rectangular.
Make your selection, then choose to go back the image menu and choose fit canvas to selection.
Now, why does all of this matter? It matters because at some point you'll want to export your image,
and when you do only those things visible on the canvas will be exported.
So while an image may be all available in the working file to click and drag around,
export is when you lose anything not visible in the canvas.
Now, this brings us to an important concept that when you are working in GIMP, you will be working in
layers. We'll delve into them in more detail, but you must always keep in mind that the canvas is
in some sense the overall container or filter for all of this, but that the layers are separate
objects with their own properties. The dimensions of a canvas are not the same as the dimensions of a
layer, or at least not necessarily so. If your canvas has the same dimensions as your layer,
we'll make it easy to work with them, but to do many of the things you will want to do, they will
end up being different. Now, if your canvas is smaller than your layer, only a portion of the layer
will come through. If your layer is smaller than your canvas, you'll need to pay attention to
placement of the layer within the canvas. This is something that trips up newbies to GIMP.
Now, the other thing to keep in mind is that unlike most office programs, there is a distinction
between your working files and your final product. Your GIMP file can contain different layers,
and these layers can be moved around on the canvas. But once you export the image, the final image
loses a lot of that. You cannot edit a JPEG image you created, and then recover all of that information.
For that reason, you should always keep your working files. They're the ones with the xcf file extension.
And hang on to those, because if there's even the remotest chance you'll want to do more editing
in the future, you'll need them. But when you want to upload to social media, export to an image
format like JPEG or PNG or GIF. So, that makes a nice little lesson. This is Ahuka for Hacker
Public Radio signing off and reminding you as always to support free software, such as the GIMP.
Bye-bye.
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 status, today's show is released
under Creative Commons, Attribution, ShareLive, 3.0 license.
