An Introduction To Filters

A short description of how filters generally work
in Gimp.

## Plug-ins

When a Photoshop user thinks of plug-ins, things like Eye Candy and Kai's Power Tools come to his or her mind. Gimp plug-ins are similar: They permit the user to add extra features to Gimp. By features, we mean filters, printer drivers, mail interfaces, save/write modules, etc. Gimp is very modular; nearly every function besides the basics is done by plug-ins.

Many Gimp users/developers have written Gimp plug-ins and made them available to the Gimp community. We encourage you to do the same. If you create your own plug-in, submit it to the Gimp community under the GPL license. Your plug-in will make Gimp even better.

In these chapters, we will discuss the Filters menu. We are going to call these filters plug-ins, because that's what most people think of when they hear the word "plug-in". The Script-Fu menu is similar to the Filters menu because Script-Fus can be applied as ordinary filters to your images. You'll find that you can make your own filters quite easily, without expert knowledge of C programming or GTK+ libraries.

Because plug-ins and scripts develop rapidly in the Gimp community, this chapter can't be as up-to-date as we would like. We encourage developers to send us mail about their new or changed plug-in so that we'll have an easier job updating this chapter. In "Compiling Plug-ins" starting on page 769, you'll find some tips on how to compile plug-ins. You may also want to visit the filter developers' home pages to get up-to-date information about the filter.

Please note that the screen shots of the plug-in dialogs won't necessarily display the same values that we used to generate the resulting image. This is because we sometimes need to exaggerate a bit so that you can really see the effects of the filter.

### Main Categories

The Filters menu includes the following submenus, which group plug-ins by function:

· Animation: Includes an animation player that lets you play Gimp animations and an animation filter that can optimize your animation, so that it uses much less disk space.

· Artistic: Includes filters to create instant artistic effects. You can easily create cubist paintings, mosaic patterns, etc. This kind of filter is mainly used for adding special effects to an image, but you can also create nice patterns with it.

· Blur: Includes many different types of blur filters. Blurring is useful when you want to soften part of a picture. Real shadows are seldom hard and solid, so to create realistic shadows you'll want to soften them up with an appropriate blur filter. A portrait may look too honest and show all the imperfections and wrinkles of the model, so blurring the portrait will help.

· Colors: Includes tools that can manipulate color and HSV values, just as if you were standing in a darkroom.

· Combine: Provides many different ways of combining several images to create a new image.

· Crypt: These filters allow you to sign, encrypt/decrypt your image or send hidden files Notice that this item is not a part of the core Gimp distribution.

· Distorts: Creates the kinds of effects you'd find in a hall of mirrors. Some of these filters are great for adding special effects to an image, like making ripples in a water surface. If you want to create textures, you'll find many useful filters here.

· Edge-detect: These filters help you find the edges or color boundaries in an image, which can be quite useful when you work with layered images and you want to strengthen or smooth the contours of an object. You can also use edge-detect filters for making easy selections with the magic wand, or easy fills with the Bucket fill tool.

· Generic: Includes mathematical filters that use a matrix for image manipulation. You can perform all kinds of manipulation with these filters, but you may need some math up your sleeve.

· Glass Effects: Includes filters that create different kinds of lens or curved mirror effects.

· Light Effects: These filters add a little glamour (extra shine, lustre, glitter or star reflections) to your designs.

· Map: Includes filters that allow you to bump map, displace or alter your image in relation to an image map.

· Miscellaneous: Includes filters that don't fit anywhere else. Currently, these include stereogram filters and video screen simulation.

· Noise: These filters will add noise effects to your image, like monitor noise, film graininess or just pointillistic artistry.

· Render: These filters will render all kinds of shapes or objects, and are extremely useful for creating textures or patterns.

Notice the handy shortcuts: Shift+Alt+f will bring up the last plug-in you used and Alt+f will apply the last filter again.

Frozenriver Digital Design http://www.frozenriver.nu Voice: +46 (0)31 474356 Fax: +46 (0)31 493833 support@frozenriver.com | Publisher Coriolis http://www.coriolis.com