GIMP User Manual
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# Glossary

# A

Alpha

  Refers to transparency. An Alpha Channel allows transpency control. Certain image formats may only contain a single Alpha Channel allowing a transparency of on or off. Other formats allow a variable level of transparency.

Anti Aliasing

  A technique used to make diagonal or curved edges appear smoother by setting pixels near the edge to intermediate colors according to where the edge crosses the underlying color.

# C

Channels

  Each image is divided up into separate channels and then recombined before being sent to the output device. An output device is most usually a screen. The channels that are used when rendering images to a screen are Red, Green, and Blue. Other output devices may use different channels. Channels can be useful when working on images that need adjustment to one particular color. If, for example, the removal of "red-eye" is the goal, work on the Red channel is most obviously a ready solution. Channels can be seen as masks that allow or restrict the output of the color that the channel represents. By running filters against this channel information, many varied and subtle effects can be put in to play by the experienced GIMP user.

Dithering

  Dithering refers to the maths and voodoo invovled in rendering an image that has few colors seem like it has many. Dithering is accomplished in different ways depending on the output device and the program. One particularly effective method is clustering pixels of color together in an attempt to simulate another color. This is achieved by the human eye and the tendancy for it to mix colors while viewing complex color patterns. A common dithering effect is seen on television screens or in newspaper print. From a distance the images seem to be contructed of many varied colors or shades, but upon closer inspection this is certainly not the case. A color television uses only three colors clustered together in various states of on or off. A black and white newspaper uses only black ink, yet pictures in newspapers appear to be constructed of grey tones. Furthermore, there are techniques used to acheive greater success in dithering. The GIMP can utilize the Floyd-Steinburg dithering technique, for example. This dithering method is simply put, a mathematical way of clustering the pixels to accomplish better results than other dithering methods. Of course, there are always exceptions and there are many different dithering models that are in use today.

# F

File Format

  A way that an image is written. You should select a file format which is suitable for your situation. JPEG and PostScript are examples of file formats.

Filter

  See: Plug-In

# G

GNU

  GNU's Not Unix, an organization devoted to the creation and support of Open Source software. GIMP is an official GNU application.

Guides

  Guides are a convenient way to help you align layers and tool functions on your drawable image, layer, or selection. Guides are created manually by clicking and dragging from either the top or left rulers in to the image area. They appear as blue dashed lines. They do not print. There are some useful options available to the user to help utilize guides efficiently, such as Snap to Guides , Toggle Guides , and Center Guide .

# H

Hex Triplet

  A way of representing color in the form #rrggbb where "rr" represents red, "gg" green, and "bb" blue. Commonly used in web design.

HSB

  See: HSV

HSL

  See: HSV

HSV

  Hue Saturation Value, a way of representing color. The Hue is the color like red or blue, the Saturation is how strong the color is and the Value is the brightness. This is sometimes called HSB or Hue Saturation Brightness.

# M

Marching Ants

  The name for the dotted line which deliniates a selection.

# P

Parasite

  A piece of information which is included in a file such as the compression type or a comment.

Perl

  A scripting language which can be used for GIMP plug-ins.

Plug-In

  Extensions to the standard GIMP feature set.

# S

Sample Merge

  Sample Merging refers to the system of taking sampling information from the sub-pixel layer of the image. Normally all pixel changes are based on a lowest resolution of one pixel. Sub-pixel operations take the information from a layer that has no lowest resolution. It is a mathematical level that uses vectors to describe the operations.

Script-Fu

  A scripting language designed specifically for GIMP.

Stroke

  A function for making a selection, path or channel into a solid line using the paintbrush.

Swap Directory

  An area on your hard disk which effectively extends the amount of main memory available to GIMP meaning larger images or more complex operations can be performed.

# T

Tile Cache

  A way that GIMP speeds up image display by keeping the data in memory.

Tool

  A mode for manipulating image functions. Paintbrush and Clone are examples of tools.

# X

XCF

  The native file format used by GIMP. XCF is an acronym for the eXperimental Computing Facility which is located at the University of California at Berkeley where The GIMP was originally written. The XCF file format supports the storage of many GIMP features, such as Layers , Alpha , and Guides.

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