How To Use the Bucket Fill Tool in GIMP {Complete Guide}

In today’s tutorial, you’ll learn everything you need to know about using the Bucket Fill tool in GIMP. If you’re ready… let’s do it!

What Is the GIMP Bucket Fill Tool?

Photo by David Waschusch

The Bucket Fill tool is one of many paint tools available to you. It’s designed to “fill” a selection, your canvas, or even line art intelligently.

Filling in a selection is essential for creating shapes since GIMP doesn’t have a native shape tool. Changing the color of a blank canvas can be quickly done with the Bucket tool too. If you have line art that you’d like to color, well, you can fill it with this tool as well.

You’re not limited to just solid colors either. With the right Tool Options set, you can fill with a pattern!

Tool Options

Click the image to enlarge.

Like any other tool, you have a variety of settings to choose from in the Tool Options. First, grab your Bucket Fill tool from the toolbar or use the keyboard shortcut, Shift + B. Once you do, the Tool Options will change based on the features for the bucket. If you can’t see the Tool Options, go to Windows > Dockable Dialogs > Tool Options to reveal the panel.

Mode

The first setting to consider is “Mode.” This sets the Bucket tool’s blending mode and determines how the pixels are applied based on the Mode chosen.

Opacity

Use this to decrease the transparency of the color fill.

Fill Type

Affected Area

Fill Whole Selection: This will fill a pre-existent selection or the whole layer.
Fill Similar Colors: This is the default setting and will fill the area according to your settings.
Fill by Line Art Detection: A new, intelligent fill type designed for coloring line art. If your line art does not have closed gaps, the tool will detect this, and the color fill will not bleed into other areas.

Finding Similar Colors

Use this to decrease the transparency of the color fill.

Fill Transparent Areas: Provides the ability to fill areas with low opacity.
Sample Merged: This allows you to toggle the sampling from one layer to all layers. If active, the fills can be made on a lower layer. Find out more about this setting from GIMP.
Diagonal Merged: This option considers the diagonally neighboring pixels for the color fill.

Threshold

You’ll use this mainly for images vs. filling an empty layer or selection with color. Increasing the Threshold will add more of the color vs. a lower setting.

Fill by

Use this to target specific color channels within the image. The components available are Composite, Red, Green, Blue, Alpha, HSV Hue, HSV Saturation, HSV Value, LCh Lightness, LCh Chroma, and LCh Hue.

This setting is complex and challenging to understand. Suppose you’ve chosen the Blue channel and click on any pixel in your image. The tool is going to search for contiguous pixels similar to the blue channel to fill with. Depending on matching colors and the Threshold setting will determine if the colors are replaced.

How To Use the Bucket Fill Tool

Created for the “Create Shapes” tutorials.

Using the Bucket Fill tool is straightforward. Select your foreground color of choice, update the settings accordingly, and click inside a selection or on the canvas. Voila! Your foreground color has been filled into the space.

Pro Tip

Instead of filling with the Bucket Fill tool, you have three other options.

Edit Menu: Use one of three options to fill with the FG, BG, or with a pattern.
Keyboard Shortcuts: Command or Ctrl + "," for the FG color, Command or Ctrl + "." for the BG color, and Command or Ctrl + ";" for filling with the currently selected pattern.
Drag & Drop: Click on the foreground or background color swatch and drag to your canvas or inside a selection. This will auto-fill the chosen color based on where you drag and release.

Line Art Detection

Let’s say you’ve created a line art illustration you’d like to fill in with color. Using the Bucket Fill tool is the quickest way to do so. Once upon a time, using it would fill your entire canvas with the colors of your choice. Since GIMP 2.10.10, the tool is much smarter than it was in earlier versions.

Now, when you click in-between some lines, the tool confines the color fill to what it perceives to be a specific area. It does this by analyzing the lines, and if it realizes there’s a gap where the line should extend to, it will stop the color from bleeding out.

This is perfect when you want to color different sections of the line art with different colors.

Tool Options

When you activate this setting in the Options panel, additional settings will be revealed. Set these according to your preference for better results.

Source: By default, this setting will consider all visible layers to determine the edges of your line art. The drop-down menu provides additional options that are self-explanatory.
Fill Transparent Areas: This will target completely transparent areas.
Feather Edges: Provides a smoother edge. Without it, the edge where the color fill stops will be jagged.
Maximum Growing Size: Increase the maximum number of pixels applied under the line art. The higher the pixel value, the thinner the edge line.
Line Art Detection Threshold: This setting utilizes the Threshold to detect contours. The higher the value, the more pixels it will detect.
Maximum Gap Length: Use this to increase or decrease the maximum number of pixels to consider closing a gap. For example, if set to 50, and your gap is larger than that, the fill will bleed out!

What's Next?

If you’re a photographer, you will rarely, if ever, use the Bucket tool. On the other hand, if you’re a graphic designer, the Bucket tool will be your new best friend. If you’d like to expand your graphic design knowledge, check out these advanced tutorials.

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