Figure 13.61. Eraser tool icon in the Toolbox
The Eraser is used to remove areas of color from the current layer or from
a selection of this layer. If the Eraser is used on something that does
not support transparency (a selection mask channel, a layer mask, or the
Background layer if it lacks an alpha channel), then erasing will show the
background color, as displayed in the Color Area of the Toolbox (in case
of a mask, the selection will be modified). Otherwise, erasing will
produce either partial or full transparency, depending on the settings for
the tool options. You can learn more on how to add an alpha channel to a
layer in Section 7.33, “
Add Alpha Channel
Figure 13.62. Eraser and Alpha channel
If you need to erase some group of pixels completely, leaving no trace
behind of their previous contents, you should check the "Hard edge" box in
the Tool Options. Otherwise, sub-pixel brush placement will cause partial
erasure at the edges of the brush-stroke, even if you use a hard-edged
If you use GIMP with a tablet, you may find it convenient to treat the
reverse end of the stylus as an eraser. To make this work, all you need
to do is click the reverse end on the Eraser tool in the Toolbox.
Because each end of the stylus is treated as a separate input device,
and each input device has its own separate tool assignment, the reverse
end will then continue to function as an Eraser as long as you don't
select a different tool with it.
3.7.1. Activating the tool
You can activate this tool in several ways:
From the image menu through
→ → ;
from the Toolbox by clicking on the tool icon
or from the keyboard using the shortcut
See the Section 3.1, “Common Features” for a description of key
modifiers that have the same effect on all brush tools.
For the Eraser, holding down the Ctrl key puts it
into “color picker” mode, so that it selects the
color of any pixel it is clicked on. Unlike other brush tools,
however, the Eraser sets the background
color rather than the foreground color. This is more useful,
because on drawables that don't support transparency, erasing
replaces the erased areas with the current background color.
For the Eraser, holding down the Alt key switches
it into “anti-erase” mode, as described below in the
Tool Options section. Note that on some systems, the
Alt key is trapped by the Window Manager. If this
happens to you, you may be able to use
Figure 13.63. Tool Options for the Eraser tool
Normally, tool options are displayed in a window attached under the
Toolbox as soon as you activate a tool. If they are not, you can access
them from the image menu bar through
→ → which opens the option window of the selected tool.
Brush; Scale; Brush Dynamics; Fade Out; Apply Jitter; Incremental
See the Brush Tools
Overview for a description of tool options that apply to many or
all brush tools.
The Opacity slider, in spite of its name,
determines the “strength” of the tool. Thus, when
you erase on a layer with an alpha channel, the higher the
opacity you use, the more transparency you get!
This option avoids partial erasure at the edges of the
brush-stroke. See above.
The Anti Erase option of the Erase tool can un-erase areas of an
image, even if they are completely transparent. This feature only
works when used on layers with an alpha channel. In addition to
the check-button in the Tool Options, it can also be activated
on-the-fly by holding down the Alt key (or, if
the Alt key is trapped by the Window Manager, by
To understand how anti-erasing is possible, you should realize
that erasing (or cutting, for that matter) only affects the
alpha channel, not the RGB channels that contain the image data.
Even if the result is completely transparent, the RGB data is
still there, you simply can't see it. Anti-erasing increases the
alpha value so that you can see the RGB data once again.
You can use the Eraser tool to change the shape of a floating
selection. By erasing, you can trim the edges of the selection.