The GNU Image Manipulation Program (GIMP) can
help you create, alter, manipulate, and enhance digital image files --
photographs, scanned images, computer-generated images, and more. This
chapter is intended to give you a quick overview of the
GIMP and its more common applications.
Like other fields, image manipulation has its own vocabulary. This
chapter cannot possibly provide complete documentation for all of the
terms and concepts needed to completely understand the
GIMP. If you want to learn more, a variety of
books are available which document the GIMP and
its capabilities, as well as the background concepts of image
manipulation. Please refer to the section called Additional Resources if you
need more information about the GIMP.
If you cannot create the right effect with the tools that the
GIMP provides, and you are not afraid to write
scripts in the Scheme scripting language, you can add a new Script-Fu to
the GIMP. A Script-Fu is somewhat analogous to
a macro in a word processing or spreadsheet application; it applies a set
series of effects (filters or other GIMP
capabilities) to a graphic or piece of text. Anyone can use the
pre-written Script-Fus included with the GIMP,
but you can also write your own. See the section called Additional Resources
for more sources of information about Script-Fus.
The GIMP can do a lot of things, but it has
some limitations. Graphic artists who create images for print media may
find the GIMP lacking, or just more difficult
to use, for pre-press applications.
For example, the GIMP cannot (yet) work in the
CMYK (cyan, magenta, yellow, and black) colorspace, which is generally
used for printing color graphics. The GIMP
instead uses the RGB (red, green, and blue) colorspace, which should be
familiar to people who have created graphics for the Web.
Since the GIMP is well-suited for creating
graphics for the Web, that is what we are going to do in this chapter.
First, we will edit a photo for display on a Web page. Then we will
create a background image, which will be tiled on the background of our
Web page. Finally, we will use the GIMP to
create a title image for the Web page.
Before we start, you will need to know some basics: how to create and save
files, and how to use the Toolbox and Dialogs.
To use the GIMP, you will need to know some
of the basics. From a shell prompt, you start the
GIMP using the command
gimp. Start the Gimp
in GNOME by going to =>
=> . In KDE, go to => =>
=> .
Like many applications, the GIMP provides
more than one method to accomplish tasks. Generally, there are three
ways to work in the GIMP:
When you start the GIMP, you will see the
Toolbox.
The GIMP Toolbox is a
palette of commonly used GIMP tools:
You can minimize the Toolbox (send it to the panel), but if you close
the Toolbox, you are closing the GIMP.
If you move your mouse over the individual buttons in the Toolbox, a
pop-up dialog will appear to identify the tool's purpose.
Click on the button for the tool you want to use in the Toolbox. The
button will then appear recessed, to indicate that it is the active
tool. The GIMP provides tools that will
crop, zoom, erase, smudge, draw, measure, blur, and more.
Generally, you use a tool on an image by activating the tool and then
clicking and dragging on your image. If a portion of the image is
selected, then the tool will only work on the selected portion.
Selections are identified by a moving dotted-line border, called
"marching ants."
Many of the tools have options. Double-clicking on the tool's button
will display the Tool Options dialog for that
tool.
Select rectangular regions This tool is used to select rectangular portions of an image.
If you click on the image, then press and hold
[Shift] while you are dragging, the rectangle
will be a square. If you click on the image, then press and
hold [Ctrl] while you are dragging, your
starting area will be the center of the rectangle (normally
the starting point is at an edge of the rectangle).
Select elliptical regions This tools is used to select circular or oval portions of an
image. If you click on the image, then press and hold
[Shift] while you are dragging, the ellipse
will be a circle. If you click on the image, then press and
hold [Ctrl] while you are dragging, your
starting point will be the center of the ellipse (normally,
your starting point is at an edge of the ellipse).
Select hand-drawn regions This tool, also known as the lasso, is used to draw a freehand
selection. Click and drag to draw a selection. When you get
back to where you started, release the mouse button.
Select contiguous regions This tool, also known as the fuzzy selection tool or magic
wand, is used to select portions of an image based on color
values. When you click once on an image with the magic wand
active, contiguous pixels with color values close to that
pixel will be selected. If you click and drag the magic wand,
a larger group of pixels will be used as the starting point.
Select regions using Bezier curves
This selection tool is similar to the freehand select tool,
but it allows you to customize your selection. If you need to
be very precise when you are selecting a complicated object,
the Bezier tool is probably the right choice for the job.
To create a Bezier selection, click to create control points
in a connect-the-dots pattern around your selection. Put a
control point at every corner or angle of your selection.
Click on the first control point you created to close the
selection. Now you can move the control points and create
curves between them to modify your selection.
To move control points, hold down the [Ctrl]
key and drag the point you want to move.
To create curves, click and drag on a control point. As you
drag away from the control point, you will see handles appear.
Click and drag on the handles to control the shape of the
curve.
If you only want to affect the curve on one side of a control
point, hold down the [Shift] key and drag on
one of the handles.
Once you have finished modifying the Bezier selection, click
inside the selection to activate it.
Select shapes from image The Select shapes from image tool (or
intelligent scissors) is intended to improve upon your
selection and automatically select the correct shape. This
tool occasionally behaves unpredictably, but give it a try.
Obviously, this type of selection is easier for the
GIMP to handle if the area that you
want to select has a distinct edge.
Click on the intelligent scissors tool in the toolbox to
activate it. Then, as if you were using the Bezier tool,
click on the image to draw a connect-the-dots pattern around
your intended selection. The intelligent scissors tool will
try to guess what you are selecting, so the lines it draws
between the control points will (hopefully) follow the edge of
your selection instead of being straight lines between the
dots. Click on the first point to complete the selection.
To refine your selection, you can move the control points by
clicking on one and dragging. Once you are happy with the
selection, click inside it to activate it.
Move layers and selections
The move tool is used to move a selected region.
Immediately after you have created an active selection, if you
move your mouse cursor over it, you will see the mouse cursor
turn into the move symbol. Click and drag on the selection to
move it. This technique works even if the move tool is not
activated in the Toolbox.
With the move tool activated, if you click and drag on your
image, you will move the entire image (or the active layer).
With the move tool activated, if you press
[Alt] and then use the arrow keys, you can move
the currently active selection outline, one pixel at a time.
Zoom in & out Also called the magnifying glass, the zoom tool is used to
enlarge (by clicking) or reduce (by
[Ctrl]-clicking) the image. You can also click
and drag to zoom in on a specific region in the image.
Alternatively, the [=] key on your keyboard will
zoom in and [-] will zoom out.
Crop the image The crop tool, which resembles a scalpel, is used to cut away
portions of an image. Click and drag to draw a rectangular
selection that you want to keep. The Crop &
Resize Information dialog will appear. Click on
the Crop button on the Crop
& Resize Information dialog to remove
everything outside the selection. Alternatively, click on the
From Selection button on the
Crop Selection dialog to make a
customizable crop box appear on the image. The control
squares at the corners of the box can then be individually
moved to refine the crop selection.
Transform the layer or selection The transform tool can be used to rotate, scale, shear, or
change the perspective of an image or selection. Double-click
on the Transform button to display the
Transform Tool dialog. Choose which
action you want to perform on the image or selection. Move
the mouse cursor over the selection or image and you will see
the mouse cursor change into the transform tool circular
arrows icon. Then click and drag on the image or selection to
perform the action that you have chosen.
Flip the layer or selection The flip tool is used to flip (or produce a mirror image) of
an image or selection.
Add text to the image The text tool is used to add text to the image. Select the
text tool and then click on the image. The Text
Tool dialog will appear. Set the parameters for
the text you want to add, type your words into the field at
the bottom of the dialog, and click on
OK to add the text. Please note that
the fonts displayed by the GIMP are
the fonts that are accessible to X on your system.
When you add text to an image, the text becomes the active
selection. If you move your mouse cursor over the text, you
will see the move icon, and you can click and drag to move the
text to an appropriate spot on the image.
Pick colors from the image The color picker is used to choose a color from the image. The
Color Picker dialog will display the
individual RGB values and the hexadecimal value for the
selected pixel. Additionally, the active color box at the
bottom of the Toolbox will change to the value of the chosen
pixel.
Fill with a color or pattern The bucket or bucket fill tool is used to fill a selection
with the active color or with a pattern.
Fill with a color gradient The blend or gradient tool is used to fill a selection with a
range of colors.
To add a gradient to a selection, first double-click on the
gradient button to display the gradient Tool
Options. The Blend pulldown
menu sets the range of colors to apply. You can blend from
the foreground color to the background color or vice versa,
you can blend from a color to transparency, or you can choose
from the many custom gradients available in the
GIMP.
You can set the "shape" of the gradient with the
Gradient pulldown menu on the gradient
Tool Options. You can also set whether
the gradient repeats or not, using the
Repeat pulldown menu.
Once you have chosen a gradient to use, click and drag on your
selection, or on the entire image, to apply your gradient.
For most gradients (but not all), the length of the drag
affects the range of the gradient; a short drag will equate
to a compact gradient with more defined edges between colors,
while a long drag will produce a wider gradient with less
clearly defined edges.
Draw sharp pencil strokes The pencil is used to draw lines, curves or shapes with sharp,
defined edges. See the section called The Brush Selection Dialog for
instructions on selecting brushes for use with the pencil.
Paint fuzzy brush strokes The paintbrush is used to draw lines, curves, or shapes with
soft edges. See the section called The Brush Selection Dialog for
instructions on selecting brushes for use with the paintbrush.
Erase to foreground or transparency Obviously, the eraser is used for erasing. See the section called The Brush Selection Dialog for brushes that can be used with
the eraser.
Airbrush with variable pressure The airbrush tool works much like an actual airbrush. You can
control how much "paint" is "sprayed." High settings are
darker and low settings are lighter and more uneven. See the section called The Brush Selection Dialog for instructions on selecting
brushes.
Paint using patterns or image regions The clone or stamp tool is used to select portions of the
image, which are then used as "paint." The clone tool can be
used to remove unwanted portions of an image, by painting over
them with patterns from the image itself.
Click on the clone tool in the Toolbox to activate it. Then
hold down the [Ctrl] key and click on the place
in the image which will supply the pattern for painting.
Release the [Ctrl] key. Click and drag to
apply the selected pattern to the image. A
+ sign will follow along with the pencil
icon of the clone tool. The + sign
starts at the spot you picked and indicates where the "paint"
is coming from in the image.
Blur or sharpen The blur/sharpen tool is used to paint a blurring or
sharpening effect on specific portions of an image.
Draw in ink The ink pen is used to draw lines similar to those drawn using
a pen; the line's thickness depends upon the speed of the
drawing device (a pen tablet or your mouse). The pen's
Tool Options include settings for the
size and shape of the pen.
Dodge or Burn The dodge/burn tool is used to adjust intensity values (the
amount of white in each pixel) in an image.
The Tool Options for the dodge/burn tool
allow you to set whether you want to dodge (increase the
intensity) or burn (decrease the intensity). The
Exposure slider sets how much you want to
change the intensity, from 0 to 100%. The
Mode sets which pixels will be affected:
Highlights, pixels with high intensity
values; Midtones, pixels with medium
intensity values; or Shadows, pixels with
low intensity values. The dodge/burn tool is used with a
particular brush; see the section called The Brush Selection Dialog for
more information about brushes.
Smudge The smudge tool is used to blur or smear an image with the
currently selected brush. See the section called The Brush Selection Dialog for more information on brushes.
Measure distances and angles The measure tool can be used to measure a distance on an
image, or to measure an angle from the horizontal.
Double-click on the measure tool and select Use Info
Window if you do not see the measurements window.
At the bottom of the Toolbox, you will see the active colors display:
The active color square is depressed; you can see in Figure 9-2 that the black foreground color
square is the active color.
By default, black is the active foreground color and white is the
active background color. To "flip" the foreground and background
colors, click on the 
.
Click on the active color box to display the Color
Selection dialog:
You can select a color "freehand." Choose one of the radio buttons
for hue, saturation, value, red, green, or blue; pick a range of
color from the middle bar; and then pick a specific color from the
color square.
You can also just type in the correct RGB values or the hexadecimal
value for the color you want to select.
As you choose colors by clicking on the color square, or by typing
in exact values, you will see the active color box on the Toolbox
change to the new color.
Color selection can provide you with some very complicated options.
If you are interested in the GIMP's color
capabilities, you should check out some of the more in-depth
resources in the section called Additional Resources.
A square on the bottom right of the Toolbox displays the active
brush, pattern, and gradient:
If you want to choose a different brush, pattern, or gradient, click
on either the active brush, pattern, or gradient to display the
palette of choices for each. Click on a choice from the palette to
make it the active brush, pattern, or gradient.
When you use GIMP drawing tools, you can
modify the attributes of the line you are drawing by selecting a
particular brush.
To display the Brush Selection dialog, click on
the active brush on the Toolbox. The Brush
Selection dialog looks like Figure 9-5:
Click on a brush in the palette to select it. Click and hold the
mouse button down to see more detail for certain brushes.
The GIMP provides six selection tools;
they are the first six buttons in the toolbox. You can use these
selection tools by clicking and dragging on the portion of the image
you want to select. The GIMP also
provides ways to modify your selection.
These modifications will only work while your selection is active.
You can recognize an active selection by the moving dotted line
around its perimeter (the marching ants).
When the mouse cursor is on your selection, the cursor becomes
the move symbol. If you click and drag on the selection, you
can move the selection.
The [Shift] key allows you to add to the
selection. Once you have an active selection, if you hold down
the [Shift] key and then use a selection tool to
select a portion of the image, the new selection will be added
to the active selection.
The [Ctrl] key allows you to subtract from an
active selection. If you hold down the [Ctrl] key
and then use a selection tool to select a portion of an active
selection, that portion will be removed.
Before you can do any image manipulation, you need to somehow acquire
an image. For example, you can scan an image, you can find one on the
Internet (be careful about copyright restrictions!), or you can take a
picture with a digital camera.
To load an existing file, click on =>
. You will see the Load
Image dialog, as shown in Figure 9-6.
The Load Image dialog displays your working
directory — the directory you were in when you started
GIMP. You can navigate up and down the
filesystem tree by double-clicking on the
Directories list on the left, then selecting a
file to open from the Files list on the right.
Filename completion is supported by the
GIMP. If you type the first letter (or
more) of a filename into the Selection field and
press the [Tab] key, the view will change to only those
subdirectories and/or files beginning with that letter or letters.
The file you select will appear in the Selection
field near the bottom of the dialog. A thumbnail preview will be
displayed on the dialog; alternatively, you will see a
Generate Preview button. If you want to see a
thumbnail of the image, click on the Generate
Preview button.
Once you have selected a file, click on the OK
button to open it. You can also double-click on a filename to open it.
To save an image file, right click on the image and choose
=> (or
). You will see the Save
Image dialog if you choose or if you choose but
the file has not been saved before.
The Save Image dialog looks almost exactly like
the Load Image dialog and navigation of the
filesystem tree and choosing files works in the same way.
When you are saving an image, you will need to choose an image format.
The GIMP supports a wide variety of image
formats. In this chapter, we are going to talk about three of them:
.gif, .jpg, and
.xcf.
The vast majority of images on the Web are in one of two formats:
.gif or .jpg. Both
formats use compression to provide smaller file sizes and shorter
download times (download speed is of paramount importance for
everything on the Web). In most other ways, these two image formats
are very different, and they are best used for different purposes.
The .jpg format is best used for photographs or
images which use a lot of different colors.
The .gif format is best used for images which
only use a few colors or which incorporate relatively large areas of
the same color.
Before the GIMP will allow you to save an
image as a .gif, you will need to convert to
indexed color or to grayscale. Convert an image to indexed color by
right-clicking on the image and then selecting
=> =>
. The Indexed Color
Conversion dialog will be displayed:
To minimize file size, a .gif image can only
display a maximum of 256 colors. When you convert to indexed color,
the RGB colors in the image are "standardized" to a particular
palette of colors. If your image is going to be used on the Web,
the safest palette choice is Use Custom Palette:
Web. The palette optimized for the Web includes the
group of 216 colors that are used by the majority of Web browsers.
After you have converted your image to indexed format, the
GIMP will allow you to save it as a
.gif file. Alternatively, if you try to save
an unconverted file as a .gif file, you will be
prompted to export the image to indexed color or to grayscale.
If you are working on an image in the
GIMP, and you want to save it in order to
work on it later, you should save it as an .xcf
file. The .xcf format is the
GIMP's native file format. If you create
an image in the GIMP, or if you open an
image and add GIMP effects (such as
layers or masks) to it, you have added information to the image
file. This information will be lost if you save the image as a
.gif or .jpg. If you save
a file as an .xcf file, you will preserve that
information. When you re-open the .xcf file,
you will be able to edit the file as if you had never closed it.
When you load an image or open a new image, the
GIMP surrounds the image with a frame which
includes helpful information and tools, as shown in Figure 9-8.
At the top, the image window displays a file identifier consisting of:
the name of the file (preceded by an * if the
file has been modified),
the window number (sequential from 0 for the first image opened
when you start the GIMP),
the view number (sequential from 0 for each image view),
the image type: RGB, Indexed, or Grayscale,
the amount of the image that can be seen in the window, depending
on if you have zoomed in on the image.
At the top left, if you click on the  icon, the image
menu will appear.
To help you visualize the size of your image, the
GIMP provides horizontal and vertical
rulers. You can toggle these off and on by right-clicking on the
image and selecting => .
At the bottom left, you will see the position of the mouse cursor on
the image, measured from 0,0 at the top left
corner.
Just above the mouse cursor position window, you will see two square
icons, which are used for creating quick masks. Basically, masks are
selections which can be saved and used again. We will not cover masks
in this elementary chapter, but if you use the
GIMP for complex images, you will find
masks to be very helpful. Please see some of the sources listed in
the section called Additional Resources for more information on masks.
Near the bottom right, you will see an icon that looks like the move
tool icon. This is called the panner. If
you are zoomed in on an image, you can click on the panner to display a
thumbnail of the whole image. Then you can click and drag on the
thumbnail to pan the image view in your image window.
Along the bottom of the window, next to the mouse cursor position
window, you will see two status fields and then a
Cancel button. The first status field displays
the file name, unless a plug-in is running (for example, if you are
applying a filter or a Script-Fu to an image). If a plug-in is
running, the name of the plug-in will appear in the first status
window. The next field is empty, but will display a status bar for a
running plug-in. Finally, the Cancel button
allows you to stop a running plug-in.
Like many other applications, the GIMP
makes it easy to accomplish tasks without taking your hands off the
keyboard. Here is a selection of helpful keyboard shortcut commands:
Table 9-1. Keyboard Shortcut Commands | Command | Keystroke | Command | Keystroke |
|---|
| copy | [Ctrl]-[c] | select all | [Ctrl]-[a] | | cut | [Ctrl]-[x] | select none | [Ctrl]-[Shift]-[a] | | invert selection | [Ctrl]-[i] | undo | [Ctrl]-[z] | | paste | [Ctrl]-[v] | zoom in | [=] | | save file | [Ctrl]-[s] | zoom out | [-] |
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