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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<title>12.5. IFS Compose</title>
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<th colspan="3" align="center" id="chaptername">12.5. IFS Compose</th>
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<td width="20%" align="left"><a accesskey="p" href="ch06s12s04.html">Prev</a> </td>
<th width="60%" align="center" id="sectionname">12.5. IFS Compose</th>
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<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="plug-in-ifscompose"></a>12.5. IFS Compose</h3>
</div>
</div>
</div>
<a id="id3372411" class="indexterm"></a>
<div class="mediaobject">
<img src="../images/filters/filters-render-ifscompose.png" />
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3372425"></a>Overview</h4>
</div>
</div>
</div>
<p>
This filter is found in
<span class="guimenuitem">Image>Filters/Render/Nature/IFS <span class="accel">C</span>ompose...</span>
</p>
<p>
This fractal-based plug-in is truly wonderful! With this
versatile instrument, you can create amazingly naturalistic
organic shapes, like leaves, flowers, branches, or even whole
trees. ("IFS" stands for "Iterated Function System".)
</p>
<p>
The key to using this plug-in lies in making very small and
precise movements in fractal space. The outcome is always hard
to predict, and you have to be extremely gentle when you change
the pattern. If you make a component triangle too big, or if you
move it too far (even ever so slightly), the preview screen will
black out, or more commonly, you'll get stuck with a big
shapeless particle cloud.
</p>
<p>
A word of advice: When you have found a pattern you want to work
with, make only small changes, and stick to variations of that
pattern. It's all too easy to lose a good thing. Contrary to
what you might believe, it's really much easier to create a leaf
or a tree with IFS Compose than to make a defined geometrical
pattern (where you actually know what you're doing, and end up
with the pattern you had in mind).
</p>
<p>
For a brief introduction to IFS's see Foley and van Dam, et
al,. <i class="citetitle">Computer Graphics, Principles and
Practice</i>, 2nd Ed., (Addison Wesley, 1990).
</p>
<p><b>The Main Interface. </b>
The plug-in interface consists of the compose area to the left, a
preview screen to the right, and some tabs and option buttons at
the bottom of the dialog. The Default setting (in the preview
window) is three equilateral triangles. (This gives rise to a
fractal pattern called the <span class="emphasis"><em>Sierpinski
Triangle</em></span>).
</p>
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3372647"></a>Options</h4>
</div>
</div>
</div>
<div class="variablelist">
<dl>
<dt>
<span class="term">Relative Probability</span>
</dt>
<dd>
<p>
Determines influence or total impact of a certain fractal.
</p>
</dd>
<dt>
<span class="term">Spatial Transformation</span>
</dt>
<dd>
<p>
Gives you information on the active fractal, and allows
you to type a value instead of changing it
manually. Changing parameters with the mouse isn't very
accurate, so this is a useful option when you need to be
exact.
</p>
</dd>
<dt>
<span class="term">Simple color transformation</span>
</dt>
<dd>
<p>
Changes the color of the currently selected fractal
component (which starts as the foreground color in the
toolbox) to a color of your choice.
</p>
</dd>
<dt>
<span class="term">Full color transformation:</span>
</dt>
<dd>
<p>
Like the Simple color transformation but this time you can manage
the color transformation for each color channel and for the alpha
channel (shown as a black channel).
</p>
</dd>
<dt>
<span class="term">Scale Hue/Value</span>
</dt>
<dd>
<p>
When you have many fractals with different colors, the
colors blend into each other. So even if you set "pure
red" for a fractal, it might actually be quite blue in
some places, while another "red" fractal might have a lot
of yellow in it. Scale Hue/Value changes the color
strength of the active fractal, or how influential that
fractal's color should be.
</p>
</dd>
<dt>
<span class="term">Render Options: Spot Radius</span>
</dt>
<dd>
<p>
Determines the density of the "brushstrokes" in the
rendered image. A low spot radius is good for thin
particle clouds or spray, while a high spot radius
produces thick, solid color strokes much like watercolor
painting. Be careful not to use too much spot radius -- it
takes a lot of time to render.
</p>
</dd>
<dt>
<span class="term">Render Options: Subdivide</span>
</dt>
<dd>
<p>
Controls the level of detail.
</p>
</dd>
<dt>
<span class="term">Render Options: Iterations</span>
</dt>
<dd>
<p>
Determines how many times the fractal will repeat
itself. (A high value for Subdivide and Iterations is for
obvious reasons a waste of process time unless your image
is very large.)
</p>
</dd>
<dt>
<span class="term">Render Options: Memory</span>
</dt>
<dd>
<p>
Enables you to speed up rendering time. This is especially
useful when working with a large spot radius; just
remember to use even multiples of the default value:
4096, 8192, 16384, ...
</p>
</dd>
</dl>
</div>
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3369891"></a>A Brief Tutorial</h4>
</div>
</div>
</div>
<p>
This is a rather complex plug-in, so to help you understand it,
we'll guide you through an example where you'll create a leaf or
branch.
</p>
<p>
Many forms of life, and especially plants, are built like
mathematical fractals, i.e., a shape that reproduces or repeats
itself indefinitely into the smallest detail. You can easily
reproduce the shape of a leaf or a branch by using four (or
more) fractals. Three fractals make up the tip and sides of the
leaf, and the fourth represents the stem.
</p>
<div class="orderedlist">
<ol type="1">
<li>
<p>
Before invoking the filter: Select
<span class="guimenu">File</span>-><span class="guimenuitem">New Image</span>
Add a transparent layer with
<span class="guimenu">Layers</span>-><span class="guisubmenu">Layers and Channels</span>-><span class="guimenuitem">New Layer</span>
Set the foreground color in the toolbox to black, and
set the background to white.
</p>
</li>
<li>
<div class="informalfigure">
<div class="mediaobject">
<img src="../images/filters/examples/ifscompose-tut1.png" />
<div class="caption">
<p>
Start by rotating triangles 2 and 3, trying
to keep them nearly the same size.
</p>
</div>
</div>
</div>
<p>
Open IFS Compose. Start by rotating the right and bottom
triangles, so that they point upward. You'll now be able to
see the outline of what's going to be the tip and sides of
the leaf. (If you have problems, it may help to know that
the three vertices of a triangle are not equivalent.)
</p>
</li>
<li>
<p>
To make the leaf symmetrical, adjust the bottom triangle to
point slightly to the left, and the right triangle to point
slightly to the right.
</p>
</li>
<li>
<div class="informalfigure">
<div class="mediaobject">
<img src="../images/filters/examples/ifscompose-tut2.png" />
<div class="caption">
<p>
Add a fourth component, then stretch, scale, and move it
as shown.
</p>
</div>
</div>
</div>
<p>
Press <span class="guibutton">New</span> to add a component to the
composition. This is going to be the stem of the leaf, so we
need to make it long and thin. Press
<span class="guibutton">Stretch</span>, and drag to
stretch the new triangle. Don't be alarmed if this messes up
the image, just use <span class="guibutton">Scale</span> to adjust
the size of the overlong
triangle. You'll probably also have to move and rotate the
new fractal to make it look convincing.
</p>
</li>
<li>
<div class="informalfigure">
<div class="mediaobject">
<img src="../images/filters/examples/ifscompose-tut3.png" />
<div class="caption">
<p>
Enlarge component 1, arrange the other components
appropriately, then select all, scale and rotate.
</p>
</div>
</div>
</div>
<p>
You still have to make it look more leaf-like. Increase the
size of the top triangle, until you think it's thick and
leafy enough. Adjust all fractals until you're happy with
the shape. Right-click to get the popup menu, and choose
<span class="guibutton">Select all</span>. Now all components are
selected, and you can scale
and rotate the entire leaf.
</p>
</li>
<li>
<div class="informalfigure">
<div class="mediaobject">
<img src="../images/filters/examples/ifscompose-tut4.png" />
<div class="caption">
<p>
Assign a brownish color to component 4, and various shades
of green to the other components.
</p>
</div>
</div>
</div>
<p>
The final step is to adjust color. Click on the
<span class="guibutton">Color Transformation</span> tab, and choose
a different color for each fractal. To do this, check
<span class="guibutton">Simple</span> and press the right color
square. A color circle appears, where you can click or
select to choose a color.
</p>
</li>
<li>
<p>
Press OK to apply the image, and voilà, you've just made a
perfect fractal leaf! Now that you've got the hang of it,
you'll just have to experiment and make your own
designs. All plant-imitating fractals (be they oak trees,
ferns or straws) are more or less made in this fashion,
which is leaves around a stem (or several stems). You just
have to twist another way, stretch and turn a little or add
a few more fractals to get a totally different plant.
</p>
</li>
</ol>
</div>
</div>
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