Note: this article covers how to use GIMP’s automatic selection tools to create selections around areas of color. If you want to learn how to use the GIMP color picker to set foreground and background colors, you’ll need to go here.
Selections are at the heart of many common image editing tasks, and GIMP has some great automatic selection tools. The two most effective tools for creating automatic selections based on color are the Fuzzy Select tool (probably more familiar to some of you as the Magic Wand tool, complete with the wand icon) and the Select by Color tool.
The two tools are almost exactly identical, except that the Fuzzy Select tool selects contiguous areas of color – in other words, a single connected area of color. The Select by Color tool will select all the areas of the chosen color across your entire image, creating multiple selection areas.
To keep things simple, the two tools are stacked in the toolbox. Right-click on the
magic wand Fuzzy Select icon or click and hold to see the stacked tools. You can also switch to Fuzzy Select using the keyboard shortcut U, or to Select by Color with the keyboard shortcut Shift + O.
Using the Fuzzy Select Tool
The settings for the two tools are almost exactly identical as well, although Fuzzy Select has an additional option, Diagonal neighbors, which allows the selection areas to consider diagonally-connected pixels as part of the same shape. This is most useful when working with large areas of single solid colors, such as pixel art and 8-bit sprites.
Antialiasing should almost always be enabled unless you are actually working on a low-resolution pixel art project, in which case you probably already know that it’s useful there.
The Feather edges setting is very useful, creating a softening effect with an adjustable radius along the edges of the selection barrier, allowing any edits or adjustments in the selection area to fade in naturally, similar to the effect of using a soft-edged brush.
Select transparent areas does exactly what it says on the tin, Sample merged tells the tool to consider all your image layers when making a selection, and we already covered the Diagonal neighbors option.
The most important setting for using the Fuzzy Select tool is the Threshold setting, which defines how similar color has to be in order to become part of the selection. A high Threshold setting selects a wider range of colors, while a low Threshold setting only selects very closely matching colors.
The Select by dropdown menu is set to Composite by default, which means that it selects from a combination of the Red, Green, Blue, and Alpha channels in the image, and this is all that’s needed for most projects. You can tell GIMP to only select from a specific channel if you want, but it can sometimes provide unexpected results unless you’re already very comfortable working with channels.
Last but not least, the Draw Mask option can be extremely helpful when deciding which Threshold and Feather edges settings to use because it will allow you to see a temporary preview of your selection area in bright pink. Sometimes, small selection areas can be difficult to spot with only a marquee outline.
Using the Select by Color Tool
As I mentioned earlier, the Select by Color tool functions almost identically to the Fuzzy Select tool, except that it can select multiple areas of color that aren’t directly connected.
For example, turning all the flowers blue at once is much easier with the Select By Color tool, which even noticed some areas of pink in the reflections and blurs that I might have missed if I selected each flower individually with the Fuzzy Select tool.
That’s all there is to know about how to select colors in GIMP! The basics are fairly easy to understand, but you’ll have to spend a bit of time using the tools and experimenting with the settings – particularly the Threshold setting – in order to get a good intuitive grasp of how it works.
At that point, colors in GIMP will be yours to command, so happy editing!About Thomas Boldt