A number of examples of brushstrokes painted using different brushes
from the set supplied with GIMP. All were painted using the
Paintbrush tool.
A brush
is a pixmap or set of pixmaps used for painting. GIMP includes a set of 10
"paint tools", which not only perform operations that you would think of as
painting, but also operations such as erasing, copying, smudging,
lightening or darkening, etc. All of the paint tools, except the ink tool,
use the same set of brushes. The brush pixmaps represent the marks that
are made by single "touches" of the brush to the image. A brush stroke,
usually made by moving the pointer across the image with the mouse button
held down, produces a series of marks spaced along the trajectory, in a
way specified by the characteristics of the brush and the paint tool being
used.
Brushes can be selected by clicking on an icon in the Brushes dialog. GIMP's
current brush is shown in the
Brush/Pattern/Gradient area of the Toolbox. Clicking on the brush
symbol there is one way of activating the Brushes dialog.
When you install GIMP, it comes presupplied with a number of basic
brushes, plus a few bizarre ones that serve mainly to give you examples of
what is possible (i. e., the "green pepper" brush in the illustration).
You can also create new brushes, or download them and install them so that
GIMP will recognize them.
GIMP can use several different types of brushes. All of them, however, are
used in the same way, and for most purposes you don't need to be aware of
the differences when you paint with them. Here are the available types of
brushes:
Ordinary brushes
Most of the brushes supplied with GIMP fall into this category. They
are represented in the Brushes dialog by grayscale pixmaps. When you
paint using them, the current foreground color (as shown in the
Color Area of the Toolbox) is substituted for black, and the pixmap
shown in the brushes dialog represents the mark that the brush makes
on the image.
To create such a brush: Create a small image in gray levels using
zoom. Save it with the .gbr extension. Click on
Refresh button in the Brush Dialog to get it in preview without it
being necessary to restart GIMP.
Color brushes
Brushes in this category are represented by colored images in
the Brushes dialog. They can be a text. When you paint with them,
the colors are used as shown; the current foreground color does
not come into play. Otherwise they work the same way as ordinary
brushes.
To create such a brush: Create a small RGBA image. For this, open
New Image, select RGB for image type and Transparent for fill type.
Draw your image and save it first to .xcf file to keep its
properties. Then save it to .gbr format. Click
on Refresh button in Brush Dialog to get your
brush without it being necessary to restart Gimp.
Tip
You can transform a selection to a brush by using the command:
Script-fu → Selection → To Brush.
Image hoses / Image pipes
Brushes in this category can make more than one kind of mark on an
image. They are indicated by small red triangles at the lower right
corner of the brush symbol in the Brushes dialog. They are sometimes
called "animated brushes" because the marks change as you trace out
a brushstroke. In principle, image hose brushes can be very
sophisticated, especially if you use a tablet, changing shape as a
function of pressure, angle, etc. These possibilities have never
really been exploited, however; and the ones supplied with GIMP are
relatively simple (but still quite useful).
Parametric brushes
These are brushes created using the
Brush Editor
which allows you to generate a wide variety of brush shapes by
using a simple graphical interface. A nice feature of parametric
brushes is that they are resizable.
In GIMP 2.2, it is possible, using the Preferences dialog, to make
key presses or mouse wheel rotations cause the current brush to
become larger or smaller, if it is a parametric brush.
One category that GIMP does not have is full-fledged
procedural
brushes: brushes whose marks are calculated procedurally, instead of being
taken from a fixed pixmap. (Actually this is not quite correct: the Ink
tool uses a procedural brush, but it is the only one available in GIMP.) A
more extensive implementation of procedural brushes is a goal of future
development for GIMP.
In addition to the brush pixmap, each GIMP brush has one other important
property: the brush Spacing.
This represents the distance between consecutive brush-marks when a
continuous brushstroke is painted. Each brush has an assigned default
value for this, which can be modified using the Brushes dialog.
3.8.1.
The GIH dialog box
Figure 2.26.
The dialog to describe the animated brush.
This dialog box shows up, if you save an image as GIMP image hose
This dialog box has several options not easy to understand. They allow
you to determine the way your brush is animated.
Spacing (Percent)
"Spacing" is the distance between consecutive brush marks when you
trace out a brushstroke with the pointer. You must consider
drawing with a brush, whatever the paint tool, like stamping. If
Spacing is low, stamps will be very close and stroke look
continuous. If spacing is high, stamps will be separated: that's
interesting with a color brush (like "green pepper" for instance).
Value varies from 1 to 200 and this percentage refers to brush
"diameter": 100% is one diameter.
Description
It's the brush name that will appear at the top of Brush Dialog
(grid mode) when the brush is selected.
Cell Size
That's size of cells you will cut up in layers... Default is one
cell per layer and size is that of the layer. Then there is only
one brush aspect per layer
We could have only one big layer and cut up in it the cells that
will be used for the different aspects of the animated brush.
For instance, we want a 100x100 pixels brush with 8 different
aspects. We can take these 8 aspects from a 400x200 pixels layer,
or from a 300x300 pixels layer but with one cell unused.
Number of cells
That's the number of cells (one cell per aspect) that will be cut
in every layer. Default is the number of layers as there is only
one layer per aspect.
Display as:
This tells how cells have been arranged in layers. If, for
example, you have placed height cells at the rate of two cells per
layer on four layers, GIMP will display: "1 rows of 2 columns on
each layer".
Dimension, Ranks, Selection
There things are getting complicated! Explanations are necessary
to understand how to arrange cell and layers.
GIMP starts retrieving cells from each layer and stacks them into
a FIFO stack (First In First Out: the first in is at the top of
the stack and so can be first out). In our example 4 layers with 2
cells in each, we'll have, from top to bottom: first cell of first
layer, second cell of first layer, first cell of second layer,
second cell of second layer..., second cell of fourth layer. With
one cell per layer or with several cells per layer, result is the
same. You can see this stack in the Layer Dialog of the resulting
.gih image file.
Then GIMP creates a computer array from this stack with the
Dimensions
you have set. You can use four dimensions.
In computer science an array has a "myarray(x,y,z)" form for a 3
dimensions array (3D). It's easy to imagine a 2D array: on a paper
it's an array with rows and columns
With a 3d array we don't talk rows and columns but
Dimensions and Ranks.
The first dimension is along x axis, the second dimension along
y axis, the third along z axis. Each dimension has ranks of cells.
To fill up this array, GIMP starts retrieving cells from the top
of stack. The way it fills the array reminds that of an odometer:
right rank digits turn first and, when they reach their maximum,
left rank digits start running. If you have some memories of Basic
programming you will have, with an array(4,2,2), the following
succession:
(1,1,1),(1,1,2),(1,2,1),(1,2,2),(2,1,1),(2,1,2),(2,2,2),(3,1,1)....
(4,2,2). We will see this later in an example.
Besides the rank number that you can give to each dimension, you
can also give them a
Selection
mode. You have several modes that will be applied when drawing:
Incremental
: GIMP selects a rank from the concerned dimension according
to the order ranks have in that dimension
Random
: GIMP selects a rank at random from the concerned
dimension.
Angular
: GIMP selects a rank in the concerned dimension according
to the moving angle of the brush.
The first rank is for the direction 0°, upwards. The other
ranks are affected, counter clockwise, to an angle whose
value is 360/number of ranks. So, with 4 ranks in the
concerned dimension, the angle will move 90°
counterclockwise for each direction change: second rank will
be affected to 270° (-90°) (leftwards), third rank to 180°
(downwards) and fourth rank to 90° (rightwards).
Speed, Pressure,
x tilt and y tilt
are options for sophisticated drawing tablets.
Examples
A one dimension image pipe
Well! What is all this useful for? We'll see that gradually with
examples. You can actually place in each dimension cases that will
give your brush a particular action.
Let us start with a 1D brush which will allow us to study selection
modes action. We can imagine it like this:
Follow these steps:
Open a new 30x30 pixels image, RGB with Transparent fill type.
Using the Text tool create 4 layers "1", "2", "3", "4". Delete
the "background" layer.
Save this image first with .xcf extension to keep its
properties then save it as .gih.
The Save As Dialog is opened: select a destination for your
image. OK. The GIH dialog is opened: Choose Spacing 100,
give a name in Description box, 30x30 for Cell Size, 1
dimension, 1 rank and choose "Incremental" in Selection box.
OK.
You may have difficulties to save directly in the GIMP Brush
directory. In that case, save the .gih file manually into
the /usr/share/gimp/gimp 2.0/brushes directory. Then come
back into the Toolbox, clic on the brush icon to open the
Brush Dialog then click on "Refresh". Your new brush appears
in the Brush window. Select it. Select pencil tool for
instance and click and hold with it on a new image
You see 1, 2, 3, 4 digits following one another in order.
Take your .xcf image file back and save it as .gih setting
Selection to "Random": digits will be displayed at random
order:
Now select "Angular" Selection:
A 3 dimensions image hose
We are now going to create a 3D animated brush: its orientation will
vary according to brush direction, it will alternate Left/Right
hands regularly and its color will vary at random between black and
blue.
The first question we have to answer to is the number of images that
is necessary. We reserve the first dimension (x) to the brush
direction (4 directions). The second dimension (y) is for Left/Right
alternation and the third dimension (z) for color variation. Such a
brush is represented in a 3D array "myarray(4,2,2)":
There are 4 ranks in first dimension (x), 2 ranks in second
dimension (y) and 2 ranks in third dimension (z). We see that there
are 4x2x2 = 16 cells. We need 16 images.
Creating images of dimension 1 (x):
Open a new 30x30 pixels image, RGB with Transparent Fill Type.
Using the zoom draw a left hand with fingers upwards. Save it as
handL0k.xcf (hand Left O° Black).
Open the Layer Dialog. Double click on the layer to open the
Layer Attributes Dialog and rename it to handL0k.
Duplicate the layer. Let visible only the duplicated layer,
select it and apply a 90° rotation (Layer/Transform/ 90°
rotation counter-clockwise). Rename it to handL-90k.
Repeat the same operations to create handL180k and handL90k.
Creating images of dimension 2 (y):
This dimension in our example has two ranks, one for left hand
and the other for right hand. The left hand rank exists yet. We
shall build right hand images by flipping it horisontally.
Duplicate the handL0k layer. Let it visible only and select it.
Rename it to handR0K. Apply Layer/Transform/Flip Horizontally.
Repeat the same operation on the other left hand layers to
create their right hand equivalent.
Re-order layers to have a counter-clockwise rotation from top to
bottom, alternating Left and Right: handL0k, handR0k, handL-90k,
handR-90k, ..., handR90k.
Creating images of dimension 3 (z):
The third dimension has two ranks, one for black color and the
other for blue color. The first rank, black, exists yet. We well
see that images of dimension 3 will be a copy, in blue, of the
images of dimension 2. So we will have our 16 images. But a row
of 16 layers is not easy to manage: we will use layers with two
images.
Select the handL0k layer and let it visible only. Using
Image/Canvas Size change canvas size to 60x30 pixels.
Duplicate hand0k layer. On the copy, fill the hand with blue
using Bucket Fill tool.
Now, select the Move tool. Double click on it to accede to its
properties: check "Move the Current Layer" option. Move the blue
hand into the right part of the layer precisely with the help of
Zoom.
Make sure only handL0k and its blue copy are visible. Right
click on the Layer Dialog: Apply the "Merge Visible Layers"
command with the option "Expand as Necessary". You get a 60x30
pixels layer with the black hand on the left and the blue hand
on the right. Rename it to "handL0".
Repeat the same operations on the other layers.
Set layers in order: Layers must be set in
order so that GIMP can find the required image at some point
of using the brush. Our layers are yet in order but we must
understand more generally how to have them in order.There are
two ways to imagine this setting in order. The first method is
mathematical: GIMP divides the 16 layers first by 4; that gives
4 groups of 4 layers for the first dimension. Each group
represents a direction of the brush. Then, it divides each group
by 2; that gives 8 groups of 2 layers for the second dimension:
each group represents a L/R alternation. Then another division
by 2 for the third dimension to represent a color at random
between black and blue.
The other method is visual, by using the array representation.
Correlation between two methods is represented in next image:
Voilà. Your brush is ready. Save it as .xcf first then as .gih
with the following parameters: Spacing:100 Description:Hands
Cell Size: 30x30 Number of cells:16 Dimensions: 3
Dimension 1: 4 ranks Selection: Angular
Dimension 2: 2 ranks Selection: Incremental
Dimension 3: 2 ranks Sélection: Random
Place your .gih file into GIMP brush directory and refresh the
brush box. You can now use your brush. Unfortunately GIMP 2.0
is bug-ridden and you may have some difficulties with brush
orientation.
Figure 2.27.
Here is the result by stroking an elliptical selection
with the brush:
This brush alternates right hand and left hand
regularly, black and blue color at random, according to
four brush directions.
![[Tip]](../images/tip.png)
