3.2.  Bucket Fill

Figure 12.18.  Toolbox Fill

Toolbox Fill

This tool fills a selection with the current foreground color. If you Shift+click and use the Bucket tool, it will use the background color instead. Depending on how the tool options are set, the Bucket Fill tool will either fill the entire selection, or only parts whose colors are similar to the point you click on. The tool options also affect the way transparency is handled.

The amount of fill depends on what Fill Threshold you have specified. The fill threshold determines how far the fill will spread (similar to the way in which the magic wand works). The fill starts at the point where you click and spreads outward until the color or alpha value becomes “too different”.

When you fill objects in a transparent layer (such as letters in a text layer) with a different color than before, you may find that a border of the old color still surrounds the objects. This is due to a low fill-threshold in the Bucket Fill options dialog. With a low threshold, the bucket tool won't fill semi-transparent pixels, and they will stand out against the fill because they have kept their original color. If you want to fill areas that are totally transparent, you have to choose right-click|Select|Select All, and make sure that the layer's “Keep Transparency” button (in the Layers dialog) is unchecked. If the Keep Transparency button is checked, only the opaque parts of the layer will be filled, and if you don't use the Select All command, only the opaque “island” that you clicked on will be filled.

3.2.1.  Activate Tool

  • The Bucket Fill can be called in the following order, from the image-menu: Tools/ Paint Tools/Bucket Fill.

  • The Tool can also be called by clicking the tool icon:

3.2.2.  Key modifiers (Defaults)


The Shift-B keys will change the active tool to Bucket Fill.


toggles the use of BG Color Fill or FG Color Fill on the fly.


toggles the use of Fill Similar Color or Fill Whole Selection on the fly.

3.2.3.  Options


The available tool options for the Fill Tool can be accessed by double clicking the Fill Tool icon.


The Opacity slider sets the transparency level for the fill. A higher opacity setting results in a more opaque fill and a lower setting results in a more transparent fill.


The Mode dropdown list provides a selection of paint application modes. A list of these modes can be found in Section 2, “ Layer Modes.


This dropdown list allows the user to select one of many fill patterns to use on the next fill operation. The manner in which the list is presented is controlled by the four buttons at the bottom of the selector.

Fill Type

GIMP provides three fill types: FG Color Fill, BG Color Fill and Pattern Fill.

FG Color Fill sets the fill color to the currently selected foreground color.

BG Color Fill sets the fill color to the currently selected background color.

Pattern Fill sets the fill color to the currently selected pattern.

Affected Area
Fill similar colors

This is the default setting: the tool fills the area with a color near the pixel onto you have clicked. The color similarity is defined by a brightness threshold, that you can set by a value or by a cursor position.

Fill whole selection

This option makes GIMP fill a preexistent selection or the whole image. A quicker approach to do the same thing could be to click and drag the foreground, background or pattern color, leaving it onto the selection.

Finding Similar Colors

Under this section you can find two options:

Fill Transparent Areas

The option Fill Transparent Areas offers the possibility of filling areas with low opacity.

Sample Merged

The option Sample Merged toggles the sampling from all layers. If Sample Merged is active, fills can be made on a lower layer, while the color information used for threshold checking is located further up. Simply select the lower level and ensure that a layer above is visible for color weighting.


The Threshold slider sets the level at which color weights are measured for fill boundaries. A higher setting will fill more of a multi colored image and conversely, a lower setting will fill less area.