User Guide

GNU Image Manipulation Program
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Chapter 17
Glossary
A B C D F G H I J L M P Q R S T U X Y
A
Alpha
An Alpha value indicates the transparency of a pixel. The smaller the alpha value of a pixel, the more visible the colors
below it. A pixel with an alpha value of 0 is completely transparent.
Within GIMP, Alpha values can be associated with the image as a whole (the Alpha Channel) and with individual layers
(a Layer Mask). You can view these by using the Channels dialog and the Layers dialog, respectively.
With some image file formats, you can only specify that a pixel is completely transparent or completely opaque. Other file
formats allow a variable level of transparency.
Alpha Channel An Alpha Channel represents the transparency of the image. Imagine you can see through the image. This
Alpha Channel is automatically added to the image as soon as you add a second layer. You can see it in the Channels
Dialog. It gives the possibility to be transparent to layers. But this possibility is not given to the background layer : for
this, you must use the ‘Add an Alpha Channel’ command.
You can also consider that an Alpha channel, although not visible, is added to every layer, except to the background layer.
The image Alpha channel is the sum of the Alpha channels of layers.
See also Alpha channel example.
Antialiasing
Antialiasing is the process of reversing an alias, that is, reducing the ‘jaggies’. Antialiasing produces smoother curves by
adjusting the boundary between the background and the pixel region that is being antialiased. Generally, pixel intensities
or opacities are changed so that a smoother transition to the background is achieved. With selections, the opacity of the
edge of the selection is appropriately reduced.
B