Don’t Understand GIMP Terms? Here are A Few Simple Definitions That Might Help

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GIMP can be pretty confusing at first, just like any complex software. In GIMP you’ll find a lot of technical photography terms, digital image terms, and even software interface terms. If you’re feeling overwhelmed by GIMP, have a look at the simple definitions of a few of these terms. I promise, most of it isn’t as complex as it seems.

What does Dialog mean?

You might the the term “dialog” in GIMP tutorials on YouTube or even read it in written GIMP tutorials.
A dialog is a window that contains options and settings for a tool or function in GIMP. For example, the interface for dealing with Layers is called the Layers Dialog.

Some of these dialogs can be docked (or attached) to other windows, like the Toolbox Window, making the dialogs and their options easily accessible when you need them. I like to keep the Layers Dialog docked at the bottom of my toolbox so I can easily access it whenever I need it without hunting for a tiny floating window.

There are instructions for docking the Layers Dialog to the Toolbox window in Chapter Two of the How to GIMP book, and two troubleshooting videos on docking dialogs on this page under “Troubleshoot Docking Dialogs”.

What does Alpha mean?

Alpha sounds like a math term, but in GIMP it just means transparency.

For example, If you go to Colors > Color to Alpha you’ll be taken to a window that lets you change any color in the image to transparent pixels. “Color to Alpha” really means “change color to transparency”.

Some functions in GIMP need to work with transparent pixels, and if your image or layer doesn’t have transparency enabled they won’t work properly. For example, if you are working with a layer and the Layer Mask option is grayed out, or the Eraser Tool isn’t working properly, you may need to add an Alpha Channel to that layer. Adding an Alpha Channel to a layer turns on the layer’s ability to use transparent pixels.

Add an Alpha Channel to a layer by right-clicking the layer thumbnail in the Layers Dialog, then choosing “Add Alpha Channel” from the list of options that pops up.

What does Delta mean?

Again, sounds like it could be a complicated term, but Delta really just means difference.

In GIMP, difference often means the contrast between pixels, since contrast can be described as the difference between light and dark. A white pixel next to a black pixel has a lot of contrast, but two middle gray pixels are less different, so we say they have less contrast.

You might encounter the term Max Delta when you’re using certain filters in GIMP. For example, the Selective Gaussian Blur filter has Max Delta as an option.

In this case Max Delta means the Maximum Difference or maximum contrast.

The Selective Gaussian Blur filter will only blur portions of the photo that have less contrast than your Max Delta setting. Pixels that have more contrast (or more difference) than the Max Delta setting will not be blurred.

What does Threshold mean?

A Threshold is a limit. You’ll see this term when you’re using some filters and tools, like the Fuzzy Select (Magic Wand) Tool.

The Threshold setting for a tool or filter is usually the limit at which the tool or filter will no longer take effect.

For example, the Fuzzy Select Tool selects regions of a photo or image that have similar colors. Setting the Threshold option for the Fuzzy Select Tool to a very low number limits the selection to very similar colors. Setting the Threshold option higher means the range of colors is broader, so the selection will include a wider range of colors.

There is also a Threshold adjustment that’s under the Color section of the Main Menu, but its use is beyond the scope of the book and this website. You can learn more about the Threshold Adjustment here.

Other Confusing GIMP Terms

Those are just a few GIMP terms that threw me for a loop when I started using GIMP years ago. There are plenty of others though, so if you ever get stuck you’ll want to know where to find out what the heck they mean.

Though it’s often a little academic, GIMP.org is my go-to source for learning exactly what the developers of GIMP mean when they use a term. The official GIMP manual is REALLY dense, but the section on function references is really useful. Just look up the tool or setting you’re trying to use to see how it’s intended to work.

Happy GIMPing!