GIMP Pocket Reference By Sven Neumann 1st Edition September 2000 1-56592-731-1, Order Number: 7311 102 pages, $9.95

Excerpt:
The Toolbox

The Toolbox, as illustrated in Figure 1, is the Gimp's main window. This first section of this book describes the functions accessible through the Toolbox's menus, its tools, and finally, the color-selector and preview areas located at the bottom of the Toolbox. The Toolbox may be resized however you like by simply dragging its borders with the mouse.

Figure 1. At the heart of the Gimp is the Toolbox, offering a variety of tools for image manipulation and design

File

The Gimp has two different File menus, one located in the Toolbox and the other in the Image window. The Toolbox's File menu (<Toolbox>File) contains only those functions specific to an image, in addition to an image history that offers easy access to images on which you have recently worked. Each image also has its own File menu (<Image>File), with options that allow you to save and print images. These options include:

New (CTRL+N)

Creates a new image. If invoked from the Toolbox, the values for the last image created in this session (e.g., image type and size), are used as the default values. (Default image values can be set with <Toolbox>File Preferences.) <Image>File New copies the properties from the current image and applies them to a new image editing window.

Open (CTRL+O)

Loads an image from disk. The Open dialog can do command-line completion (i.e., pressing the TAB key will complete the filename if there are no ambiguities). Hidden files and directories are not displayed in the dialog, but can be directly accessed by entering their names. Pressing SHIFT or CTRL while selecting the filenames allows you to open multiple images at the same time. Shift-clicking allows you to select a range of images in a directory, while control-clicking allows you to select specific files.

Saving an image also creates and saves a small preview of the image. The Gimp uses the same file format for the preview that the program xv uses for its own previews. This preview is displayed in the file list. Clicking the preview causes an up-to-date preview of the image to be generated. If all of the files in the list have been selected and the preview area is clicked, previews are generated for each image.

The Gimp recognizes the image by reading the first few bytes of data (the file format's "magic number"). If the Gimp fails to identify the image type, it will try to do so based on its file extension. If you want to load a valid image file whose extension is not correct, the file type can be set manually by selecting it from the Determine File Type menu. Compressed files with the .gz or .bz2 extensions are decompressed automatically when opened if the gunzip or bunzip2 programs are installed on your system.

Acquire

Plug-ins that load images from somewhere other than the hard disk (e.g., scanners) are placed here. Xsane, a Unix front-end for the SANE scanner library, cooperates especially well with the Gimp. The Windows version of the Gimp has a plug-in that can communicate with scanners via the TWAIN interface.

Screen Shot

A front-end to the xwd program in the Unix version of the Gimp; a separate plug-in is available for the Windows version. A single window, with or without window manager decorations (e.g., title bar or window frames) or the entire desktop can be the focus of the screenshot. If a single window is to be dumped, the cursor will change to a cross after the GRAB button is pushed; the screenshot of the desired window can be grabbed by simply clicking it.

Preferences

Offers configuration options for Gimp internals and the GUI. The settings are described later in the "Preferences" section.

Dialogs

Gives access to a number of dialogs, which are covered later in the "Dialogs" section.

Quit (CTRL+Q)

Quits the Gimp. If any image has not been saved since its last change, the Gimp will ask you whether you want to quit without saving changes.

Xtns (Gimp Extensions)

Gimp's extensions are accessible though the Toolbox's Xtns menu. Most functions found in the Xtns menu are plug-ins or scripts that, in contrast to the filters found in the Image menu, are not associated with a specific image. The extensions include:

Module Browser

Some functions of the Gimp are implemented as modules (e.g., the color selection dialog). The Module Browser displays a list of all loaded modules and offers the ability to inhibit the automatic loading of modules, which can save launching time and memory.

DB Browser

The Gimp places its internal functions in a Procedural Database (PDB), allowing them to be called by plug-ins and scripts. Furthermore, plug-ins and scripts add their own calling function to the database so they can execute each other. The DB Browser displays the functions that have been added to the PDB, as well as their input and output parameters.

PDB Explorer (Perl)

An alternative to the DB Browser, written in Perl.

Plug-in Details

This function displays a list of all available plug-ins, which can be searched for by name. This is a nice feature to use when you can't remember where a certain plug-in resides in the menu hierarchy.

Parasite Editor (Perl)

The Gimp uses parasites to save plug-in settings, either globally or on a per-image basis. This editor offers access to the parasites, although you shouldn't have to edit anything in this dialog.

Unit Editor

The Unit Editor offers an easy way to modify the unitrc file. If your favorite unit (e.g., furlongs or fathoms) is not yet present, you can add it to the Gimp using the Unit Editor.

Perl (Perl)

Since Version 1.0, the Gimp's support of scripting languages has expanded from the original Script-Fu to include Python and Perl. The Perl menu allows access to the Perl Control Center (PCC), which contains information about the Perl installation and a logfile of error messages. The Perl server, which lets external Perl scripts control the Gimp remotely, is launched from here as well.

Render (Perl)

This menu includes some scripts that generate logos or nice effects. All functions in this menu are implemented in Perl.

Script-Fu

In addition to a whole slew of web-graphic and logo scripts, this menu contains the Script-Fu Console. Here, you can enter Script-Fu commands (Script-Fu is a Scheme dialect). Refresh ing will make the Gimp re-read scripts, enabling scripts and changes to be added without having to restart the Gimp.

Split Video to Frames

The same menu as found under <Image>Video.

Web Browser

If the Netscape browser is installed on your system, the Web Browser menu offers direct links to a variety of web pages on the official Gimp web site (http://www.gimp.org/), and to other Gimp-related sites on the Internet.

Help

The Gimp has a built-in help system that can be accessed from the Toolbox (<Toolbox>Help), or by pressing F1. It's important to note, however, that the Gimp's help system is incomplete. It includes:

Help (F1)

Opens the Gimp's help browser.

Context Help (SHIFT+F1)

Changes the cursor to a question mark. Point and click on an icon or GUI element, and the help browser will open and tell you about its use.

Tip of the Day

Shows the Tip of the Day. Going through these tips once is definitely worth the effort.

About

Shows the version of your Gimp installation and lists the names of its developers.

Tools

The Gimp's tools are displayed as icons in the Toolbox. Clicking an icon selects the corresponding tool. Double-clicking the icon opens an option window for that particular tool.

This section lists the Gimp's tools in the same order as they appear in the Toolbox, starting with the upper-left button, the Rectangular Selection tool. Functions hidden in some menus can be regarded as tools; these will be explained in the section corresponding to their positions in the menu structure, and are marked by an icon next to their names.

If a tool's function is invoked by dragging the mouse (with the exception of the drawing tools), it may be canceled even before the function takes effect by pressing and holding down the right mouse button while releasing the left mouse button.

Selection Tools

Selection tools are important utilities in image manipulation. They are used to define selection masks (a marked area) upon which functions can be applied exclusively. The Gimp marks the border of a selection with an animated dashed line. A selection doesn't necessarily require a clearly defined border. You can also have the border of the selection fade out softly. This is done by using the Feather Radius option, which is common to all selection tools. Feathered selections display border markers with pixels reduced by 50 percent. Another option available with all selection tools is Antialiasing, which eliminates the staircase effect at the selection's border.

A selection, along with its contents, can by moved by dragging it with the mouse. This will implicitly convert the selection into a floating selection. To move the border of a selection without its contents, press ALT while dragging the mouse.[1]

Selection tools usually create a new selection, but it is possible to combine the new selection with an existing one. The mode of combination depends on which key is being held down when the mouse button is pressed. This is outlined in Table 1, which shows the keyboard-click combinations.

Table 1: Keyboard-Click Combinations

Key	Action
SHIFT	Addition
CTRL	Subtraction
SHIFT+CTRL	Intersection

The <Image>SelectBy Color menu item provides an additional means of selecting a region, but it is not covered in the following list, since it is not present in the Toolbox. This tool selects areas based upon their color (see "By Color" in the "Select" section).

 

Rect Select (R) and Ellipse Select (E)

These tools create rectangular and elliptical selections, and behave very similarly. Dragging creates a selection, which is fixed once you release the mouse button. To deselect a selection, just click on the canvas outside of the selected area.

The CTRL and SHIFT keys add an additional function to these tools. While holding down the key and pressing the mouse button, you can determine the way that the current selection and an existing one are combined. The key that is pressed when the mouse button is released determines the geometry of the new selection. Table 2 shows the keyboard-click/release combinations for the rectangular and elliptical selection tools.

Table 2: Keyboard-Click/Release Combinations

Key	Before Mouse Button	After Mouse Button
SHIFT	Addition	Square or circle
CTRL	Subtraction	Origin defines the center
SHIFT+CTRL	Intersection	Square or circle around the center

These functions can be used in any combination. For example, imagine you want to cut a circle out of an existing rectangular selection. To do this, use the elliptical selection tool (E) and place the cursor over the existing rectangular selection. Hold down the CTRL key while pressing the mouse button, and then press and hold SHIFT+CTRL while dragging the mouse and releasing the mouse button. The selection is now a fixed elliptical area centered on the rectangle. The keyboard-click/release functions include:

Fixed Size/Aspect Ratio

Creates a selection with a fixed size. Pressing SHIFT while creating the selection creates a selection with a variable size but a fixed aspect ratio.

 

Free Select (F)

Use this tool to select an area by tracing an outline with the mouse. When the mouse button is released, the selection is closed by joining the starting and ending points with a straight line.

 

Fuzzy Select (Z)

The Fuzzy Select tool or "magic wand" selects a contiguous area around the indicated pixel. Neighboring pixels with a similar color to that of the selected pixel are included in the selection. The color threshold can be set in the Threshold option or by dragging the mouse while the mouse button is being held down.

Sample Merged

Takes the colors of other layers into account, if these are visible.

Threshold

Sets the maximum deviation allowed for a pixel to be included in the selection region.

 

Bezier Selection (B)

This tool creates and manipulates paths. Paths are implemented as Bezier curves with control points, offering the ability to edit the tangent of a curve at each point. To create a bezier selection, you first need to define the curve's vertices. This is done by clicking the canvas. After closing the path by placing the final vertex on top of the first, you can edit the vertices and connect lines of the curve. To edit a point, select it by clicking on it. You can change the tangent at this point by dragging the mouse. Pressing SHIFT allows you to edit more than one connecting line at a time. Dragging the mouse with CTRL held down moves the vertices freely around the canvas. To select a curve, click in the area enclosed by the curve. The Paths dialog (see "Layers, Channels, and Paths") contains a list of the currently available paths, and offers a set of tools with which the paths may be further manipulated.

Any selection can be converted to a path by selecting <Image>SelectTo Path, which makes paths powerful tools for manipulating selections.

 

Intelligent Scissors (I)

While almost useless in Version 1.0, Intelligent Scissors has become a very powerful tool for selecting complex image contents. Clicking on an image sets control points, and the Gimp tries to connect them by finding and following strong contrasts in the image. Any control point besides the starting or ending point can be moved by clicking and dragging it to a new position. The area that is to be selected is closed by placing a final control point on top of the first one; after this, you may select an area by clicking into it.

Transform Tools

Possible transformations include moving, rotation, flipping, and magnifying. The Gimp's tools for performing such transformations follow.

 

Move Tool (M)

With the Move tool, an entire layer or an existing floating layer can be moved by simply dragging it with the mouse. The layer that has a visible pixel at the cursor's current position is moved. This allows picture elements to be moved intuitively. You can force the active layer to be moved by pressing SHIFT while clicking the mouse button, even if it does not contain opaque pixels at the given position.

You can also use the cursor keys to position layers. Press a cursor key to move a pixel in a given direction. Press SHIFT while using the cursor keys to move the layer in 25-pixel increments.

The Move tool can also be used to create and position guide lines. To create a guide, click on the rulers at the top or right of the Image window. This automatically selects the Move tool. Now you can drag a guide onto the image. Use the Move tool to reposition the guides in the image. To delete guides, simply drag them back onto the ruler. Guides can be set precisely with the Measure tool (see "Paint Tools").

 

Magnify Tool (SHIFT+M)

The Magnify tool changes the magnification level of the image display. Select the area to zoom into by dragging the mouse. Simply clicking onto the image will zoom in at the given point by one magnification step; CTRL and click will zoom out. The Gimp can display magnification levels in the range of 1:16 to 16:1. If the Dot for Dot option is enabled, a zoom level of 1:1 means that one image pixel corresponds to one pixel on your screen. Otherwise, the image is displayed with the correct length and height (assuming that you specified your monitor resolution in Preferences; see ). Some accelerator keys have been defined for the zoom tool (see "View").

Allow Window Resizing

Adjusts the window to fit the zoomed image, if possible.

Tool Toggle

Toggles between zooming in and out, using the CTRL key.

 

Crop & Resize (SHIFT+C)

This tool can be used to resize the image or a single layer. Select an area by dragging the mouse. The area will be surrounded by a frame. The top-left and bottom-right corners of the frame can be used for resizing, while the other two corners will repostion the frame. Depending on the status of the Allow Enlarging option, the edges of the frame are either limited to the image area, or may extend beyond the image borders. This option can be toggled by pressing the ALT key.

The exact position and dimensions of the frame can be set in the dialog window that appears as soon as this tool is used. Clicking the From Selection button in this dialog box adjusts the frame to fit an existing selection or, if no selection exists, the entire image.

The Auto Shrink function works in a similar way to Autocrop ; it shrinks a selected area automatically until the colors at the edges of the selected area differ. This enables a precise selection of free-floating picture elements.

Clicking inside the selected area will crop the image; every part of the image (or, if Current Layer Only has been selected, the current layer) outside the frame is discarded unless Resize has been selected. If Resize has been selected, the parts outside the frame are not thrown away; they are kept and can be made visible again with another Resize. This option can be toggled with the CTRL key.

Current Layer Only

Performs the action only on the current layer, instead of on the entire image.

Allow Enlarging

Allows the crop frame to enlarge beyond the borders of the image (ALT).

Tool Toggle

Toggles between Crop and Resize (CTRL).

 

Transform Tool (SHIFT+T)

The Options dialog offers four different transformations:

Rotation

For rotating the current active layer or selection. The rotation angle is set by dragging the mouse. Holding down CTRL forces the angle to be a multiple of 15. Rotations by multiples of 90 degrees are performed faster by using the corresponding function from the <Image>Layers or <Image>Image Transforms menu.

Scaling

For free scaling. Holding down SHIFT allows you to scale only vertically. Use CTRL to scale only horizontally. Holding down both SHIFT and CTRL will maintain the image's aspect ratio during scaling.

Shearing

For shearing a selection or the active layer. Shearing transforms a rectangle into a parallelogram. The direction of the first mouse movement determines if the shearing will be done horizontally or vertically.

Perspective

For distorting the image's perspective by dragging the corners of an overlaid mesh. This is the most general of the transformation tools.

The transformation can be done in two different ways. If Tool Paradigm Traditional is selected, the mesh describes the image after the transformation. On the other hand, if Corrective mode is used, the transformation works the other way around--the mesh indicates which image lines will be horizontal or vertical after the function is applied. This mode is especially useful for correcting slightly rotated scans or perspective distortions in photos. The result of a Corrective transformation can be much bigger than the original. In this case, the Clip Result option will crop parts that go beyond image boundaries.

All transformation functions are very CPU-intensive. Larger images take a while to transform, so either be prepared for a coffee break, or turn Smoothing off.

If the image contains locked paths (indicated by a small padlock to the left of the path preview--see "Paths" ), the paths are transformed along with the image.

Tool Paradigm

Determines how the transformation is applied.

Smoothing

Considerably enhances the quality of the transformation result.

Clip Result

Crops the image to the original image boundaries after the transformation.

Show Path

Displays the paths, if they are locked (see Path Dialog ).

 

Flip Tool (SHIFT+F)

Flips the selection of the active layer. You can choose the direction of the flip in the Options dialog or by toggling this setting with the CTRL key.

Tool Toggle

Toggles between horizontal and vertical flipping using the CTRL key.

 

Text Tool ( T )

Inserts text into an image. Clicking the image after selecting this tool opens the text dialog. Here, you choose a font from those offered by the X server, select its size, and enter the text. Multirow text has to be entered one row at a time, as the Gimp does not yet support text in multiple rows. The text is inserted into the image as a floating selection and should be converted to a layer to make subsequent corrections easier. Multirow text has to be entered either by repeated use of the text tool, or by using the Dynamic Text plug-in (described later in this section), which allows you to edit text after it has been rendered.

Antialiasing

Prevents staircase effects at diagonal lines. This is done by calculating the text for three times the given size and scaling it back down.

Border

Creates a border of the given pixel size around the text. This border is not visible--it just enlarges the text layer. This can be useful if the text is to be manipulated (e.g., blurred) afterward.

NOTE: The Gimp has a tendency to crop some italic fonts. This is a bug in the X server that returns incorrect font sizes. Border can help by defining the shape of the text.

Use Dynamic Text

Invokes the Dynamic Text plug-in instead of the standard text tool.

 

Color Picker (O)

The foreground color is set to the hue of the selected pixel. A pop-up window displays information about the color composition and the color's hexadecimal code, for use in HTML (e.g., #000C78 or #FFCC00).

Sample Merged

Uses the color that is actually seen. This color may be created by overlapping several layers with different colors.

Sample Average

Returns the average color over an area.

Update Active Color

Copies the selected color to the currently active color in the Toolbox (either the fore- or background color, whichever is selected in the Toolbox).

Paint Tools

The Gimp's drawing tools use the active brush, which can be set in the Brush dialog (<Image>DialogsBrushes) or by clicking the brush preview in the Toolbox. The brush determines the shape and size of the applied color. The Global Paint Options (see "Preferences") determine if the opacity and mode of applying the color canvas (see "Color Models") is the same for all drawing tools. If the option is active, Opacity and Mode are associated with the brush and can be set in the Brush dialog. Otherwise, they can be set individually for each drawing tool in the tool's Options dialog.

All drawing tools let you draw straight lines: pressing SHIFT and clicking the mouse draws a straight line to the last place the tool touched the canvas.

If you are using a graphic tablet with a pressure-sensitive pen, you might be interested in the pressure information options that some tools offer. Pressure Sensitivity options can be combined in any given way; however, not all tools offer all of the following options:

Opacity

Controls the opacity of the color applied.

Pressure

Makes the brush act as if it were harder or softer.

Rate

Influences the setting rate of the active tool. This does not work with all tools.

Size

Changes the size of the brush.

Color

Uses a color from the current gradient instead of the foreground color. The pressure determines the position at which the color is taken from the gradient.

If pressure-sensitive input devices are not used (or not configured; see ), these settings will have no effect.

 

Bucket Fill (SHIFT+B)

Color is poured into the selected position, spreading until it meets pixels whose color difference to the selected pixel surpasses a given threshold. If a selection exists, the whole selection is filled. To fill an entire layer, select it first (CTRL+A). A much faster way to achieve this is to drag and drop the color from any color field (e.g., fore- or background color in the Toolbox) into the selection.

Threshold

Specifies a threshold at which the color flow will stop.

Sample Merged

While only the color of the pixel in the active layer is normally considered, this option uses the color that is actually seen. This color may be composed of several different layered colors.

Fill Type

Either the foreground color (Color Fill ) or the currently selected pattern (Pattern Fill ) is used. CTRL toggles the used color between fore- and background color.

 

Blend (L)

Introduces a gradient color to the image. Dragging the mouse sets starting and ending points. Pressing CTRL while dragging forces the angle between the starting and ending points to be a multiple of 15 degrees. A color gradient is created along the connecting line. This tool has many options, which can be discovered by experimenting and trying out different combinations.

Opacity

Controls the overall opacity of the gradient, from transparent to completely opaque.

Offset

Indicates the distance from the starting coordinate at which the blend should actually begin. The offset is expressed as a number from 0 to 100 that describes a proportionate distance between the starting and ending coordinates.

Blend

There are a few ways to blend colors:

FG to BG (RGB)

Blends from foreground to background color through RGB color space.

FG to BG (HSV)

Blends from foreground to background color through HSV color space. Creates rainbow-like gradients.

FG to Transparent

Blends from foreground color to transparency.

Custom Gradient

Uses the active gradient from the Gradient Editor (<Image>DialogsGradient Editor).

Gradient

There are a few types of gradients:

Linear

Along the line from the starting to the ending point.

Bi-linear

Along the line from the starting point to the middle, and from the middle to the ending point with reverse orientation.

Radial

A circular blend. The starting point defines the center of the circle; the ending point, the radius.

Square

A square blend. The starting point defines the center of the square; the ending point is on the edge.

Conical

Blending around the starting point in a circle. Either once around (Asymmetric option) or back and forth (Symmetric option).

Shapeburst

Starting and ending points are not defined. According to the shape of the active selection, Shapeburst creates a three-dimensional effect. The Angular, Spherical and Dimpled options set the smoothness of the implied body.

Spiral

A spiral blend around the starting point, which is interpreted as the center point of the blend. The spiral is created with either a Clockwise or Anticlockwise (counter-clockwise) rotation. The distance between the starting and ending points determines how dense the spiral is.

Repeat

Determines how the gradient is repeated beyond the bounding points, including the following ways:

None

No repetitions. The color remains constant beyond the bounding points.

Sawtooth Wave

The gradient is repeated with the same orientation.

Triangular Wave

The gradient is repeated with alternating orientations.

Adaptive Supersampling

Significantly enhances the quality of the gradient, but uses more CPU time.

 

Pencil (SHIFT+P)

The Pencil tool has a hard tip, applying color with full force over all of the brushed surface. This means that even if the brush has a soft fading edge, the edges of the drawn lines will still be hard. The pencil is useful for drawing fine contours and editing single pixels.

Incremental

Has an effect only if a brush with semi-transparent pixels is used. The opacity of the applied color increases each time the brush passes over an area.

 

Paintbrush (P)

The Paintbrush draws exactly the way the brush is shown in the dialog. Diagonal lines do not have the aliasing effect because of the smooth edges of the brush. Thin, straight lines usually seem too worn out; the pencil is a better tool for creating these.

Incremental

Increases the opacity of the painted colors when the same area is painted over repeatedly. Works with semi-transparent brushes only.

Fade Out

Fades the Paintbrush during the drawing, as if it were running out of paint. The value determines how long the color will last. This option can be disabled with a value of zero.

Gradient

Takes the color from the currently active gradient, as shown in the Toolbox. Different modes of application can be specified in the menu:

Once Forward

Uses all colors in the gradient from start to finish exactly once.

Once Backward

Does the same thing as Once Forward, only from back to front.

Loop Sawtooth

Starts using colors from the front once the Paintbrush reaches the final color.

Loop Triangle

Continuously goes through the gradient from front to back to front again. The length of the gradient can be entered in the input field for this option.

 

Eraser (SHIFT+E)

The Eraser makes pixels transparent, or, if it is used on a layer without an Alpha channel, the pixels turn to the current background color instead.

Incremental

Increases the transparency of the pixels when the same area is painted over repeatedly. Works with semi-transparent pixels only.

Hard Edge

Gives the eraser a hard edge, like a pencil.

Anti-Erase

Has an effect only in layers with an Alpha channel. Anti-Erase applies the eraser effect backward--instead of adding transparency to erased pixels, it makes them more opaque. This setting can be toggled with CTRL.

 

Airbrush (A)

The Airbrush applies color gradually. The longer the Airbrush remains at the same place, the more color applied at this position, and the bigger the color splotch.

Incremental

Increases the transparency of the pixels with each pass when the same area is repeatedly painted over. This works with semi-transparent pixels only.

Rate

Gives the amount of color applied per time unit. Low values result in smooth lines, high values show unsteady spray effects.

Pressure

Determines how much color is applied in the first moment this tool is used.

 

Clone (C)

This tool is used to copy an area of an image; after selecting an image area as a source, this part of the image can be applied to a different area using the brush. The source is selected by clicking the desired position while holding down CTRL. During cloning, a small cross shows the current position from which image parts are copied. Source and destination do not have to be in the same image. For example, you can clone a section from any image into another.

Source

If Pattern Source is selected instead of an image area (Image Source), this allows the use of the active pattern shown in the Toolbox as a source.

Alignment

Determines if the source and destination stay in relation (Aligned ) or if the source is reset to the originally indicated position when the mouse button is released (Non-Aligned ). Registered Alignment makes sense only when cloning from another image. This makes the Clone tool use the same coordinates for the source image and the destination image.

 

Convolver (V)

Depending on the options set, this tool can either Blur or Sharpen images. To sharpen larger image areas or an entire image, use the Sharpen or Unsharp Mask filters (<Image>FiltersEnhance).

Rate

Determines the strength of the effect.

Convolve Type

Sets the effect of the Convolver tool (Blur or Sharpen). The setting can be toggled using the CTRL key.

 

Ink Tool (K)

The Ink tool is the only drawing tool that does not use the brush selected in the Brush dialog. Instead, the form and size of the Ink tool's brush is set in the Options window, which can be accessed by double-clicking on the Ink tool icon in the Toolbox. This tool was specifically developed for use with a graphics tablet, where the pressure and angle of the pen, as well as the pen's speed, determine how ink is applied to an image.

Adjustment

Specifies size and orientation of the brush.

Sensitivity

Determines how much the pen's pressure influences the brush size, and how the tile affects the brush shape. You can regulate how much smaller the brush gets if the pen is moved very quickly.

Type

Selects one of several different basic brush shapes.

Shape

Allows you to modify the brush shape by elongating it in a specific direction by dragging the mouse.

 

Dodge or Burn (SHIFT+D)

This tool simulates darkroom photo development techniques. Dodge darkens the image parts that it passes over, while Burn makes them brighter. These effects do not use the current foreground color.

Exposure

Sets the strength of the effect.

Type

Selects one of two effects: Dodge or Burn.

Mode

Determines on what image parts the effect will be more pronounced.

 

Smudge Tool (SHIFT+S)

Smudge simulates the smearing of wet paint. The brush picks up some of the color that it passes over and paints with it for a little while.

Rate

Determines how long the chosen color remains in the brush.

 

Measure Tool

This tool measures the distances and angles between points in the image. To measure the distance between two points, simply click on one and drag the mouse to the other--the distance is shown in the status bar at the bottom of the image. The points can be repositioned after they have been set. Pressing CTRL while dragging forces all movement to be horizontal, while pressing ALT constrains movement to vertical. Clicking on a set point while pressing SHIFT enables you to set another point by dragging the mouse to its position; the angle between the two connecting lines is shown as well.

The CTRL and ALT keys will place horizontal and vertical guides, respectively, into the ending points. Guides can be placed with a high degree of precision this way (see "Move Tool" ).

Use Info Window

Opens a window that displays the distance and angle between the points and connecting lines just as the status bar does.

Color Selection

The current foreground (top-left) and background (bottom-right) colors are shown in the Toolbox. Double-clicking the color panels opens the color selection dialog. Pressing X or clicking on the double arrow exchanges the two colors. Pressing D or clicking on the lower-left icon resets the colors to the default colors (black and white). These color fields are also the source and destination for drag-and-drop operations, which enable you to drag a color to the color selection of a plug-in or script.

Four tabs in the dialog offer different ways to select a color:

GIMP

Shows an area in which two color channels can be altered. To the right, a third channel is modifiable. One of the checkboxes to the right controls the third channel. Any of the channels from RGB and HSV can be selected (see "Color Models").

Watercolor

Imitates the mixing of watercolors. You can take some color from the left field by clicking the left mouse button; right-clicking will release the selected color.

Triangle

Enables the selection of a color that comes close to the subjective color perception. Rotate the triangle to alter hue. The saturation and brightness can be selected from the triangle itself.

GTK

Displays the standard GTK Color Selection dialog--the same dialog used by plug-ins and scripts. Hue and saturation are set in the circle to the left, while brightness can be selected in the field to the right.

Brush, Pattern, and Gradient Display

These areas display the current active brush, pattern, and gradient. A selection dialog is invoked by clicking onto the corresponding field (see "Dialogs"). In addition, these areas are used as source and destination points for drag-and-drop operations.

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1. If the Image window moves instead of the selection, your window manager reserves the ALT key for itself. In this case, reconfigure your window manager so that it frees the ALT key for the Gimp.

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