User Guide
GNU Image Manipulation Program
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File Format
A file format or file type is the form in which computer data is stored. Since a file is stored by an operating system as a
linear series of bytes, which cannot describe many kinds of real data in an obvious way, conventions have been developed
for interpreting the information as representations of complex data. All of the conventions for a particular ‘kind’ of file
constitute a file format.
Some typical file formats for saving images are JPEG, TIFF, PNG and GIF. The best file format for saving an image
depends upon how the image is intended to be used. For example, if the image is intended for the internet, file size is a
very important factor, and if the image is intended to be printed, high resolution and quality have greater significance. See
Format types.
Feathering
GIMP uses the process of Feathering to make a smooth transition between a region and the background by softly blending
the edges of the region.
In GIMP, you can feather the edges of a selection. Brushes can also have feathered edges.
Floating Selection
A floating selection (sometimes called a ‘floating layer’) is a type of temporary layer which is similar in function to a
normal layer, except that a floating selection must be anchored before you can resume working on any other layers in the
image. You can use various operations to change the image data on the floating selection. There can only be one floating
selection in an image at a time.
You can anchor a floating selection in various ways. First, you can create a New layer. If you create a new layer while
there is a floating selection, the floating selection is anchored to it. Second, you can anchor the floating selection to the
current layer, the selection is originating from. To do this, click anywhere on the image except on the floating selection.
This merges the floating selection with the current layer. You can also anchor the floating selection to the current layer by
clicking on the anchor button of the Layers dialog or using the Anchor layer command (Ctrl-H).
There are also various ways to create a floating selection. The first is to convert an existing selection into a floating selection
with the Float command. The ‘paste’ operations, Paste Named Buffer, Paste or Paste Into, also create a floating selection.
In addition, the Transform tools, Flip, Shear, Scale, Rotate and Perspective, create a floating selection when they are used
on a selection, rather than a layer. When the Affect mode is Transform Layer and a selection already exists, these tools
transform the selection and create a floating selection with the result. If a selection does not exist, they transform the
current layer and do not create a floating selection. (If the Affect mode is Transform Selection, they also do not create a
floating selection.) You can also create a floating selection by clicking on a selection and dragging it.
Floating selections are a rest of the time when GIMP did not use layers. They have no practical use, but you must know
what you have to do with them.
Floyd-Steinberg Dithering
Floyd-Steinberg dithering is a method of dithering which was first published in 1976 by Robert W. Floyd and Louis
Steinberg. The dithering process begins in the upper left corner of the image. For each pixel, the closest available color in
the palette is chosen and the difference between that color and the original color is computed in each RGB channel. Then