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<chapter id="selections">
<title>Selections</title>
<para>
This chapter gives a short introduction on selections.
</para><para>
You can select a part of an image masking off the rest. This is handy when
you want to cut, copy or just modify a part of the image without affecting
the rest. For processing selected objects &chalk; applies a mask. Each pixel of
the selection is processed based on a value of its mask, or the <quote>level
of the selection</quote>, that can range from 0 (unselected) to 255
(selected). Yes, that is right, you can have fractionally selected pixels.
And by working on individual pixels you can <quote>paint</quote> your selection.
</para><para>
The selection mask is visualized with unselected pixels having a blueish
tint, and selected pixels looking like normal. Fractionally selected pixels
are shown as something in between. Additionally a red border is drawn around
the selected areas. Fractionally selected pixels are inside the border, so
even inside the red border you can possibly see the blueish tint on some pixels.
</para>
<sect1 id="selections-making">
<title>Making a selection</title>
<para>
A whole range of tools exist to make selections. From rectangles, ellipses
and freehand to the more exotic like color range select. When you make
several selections they add up. So a rectangle select followed by an
ellipse select select both areas. Later on, you can subtract areas from
the selection by using, for example, the <guilabel>Erase Selection</guilabel> tool.
</para><para>
To get back to normal (no active selection), choose
<menuchoice><guimenu>Select</guimenu><guimenuitem>Deselect</guimenuitem>
</menuchoice>. To select all pixels, choose
<menuchoice><guimenu>Select</guimenu><guimenuitem>Select All</guimenuitem>
</menuchoice>.
</para><para>
You may think that those two actions give the same result, but it
is much more efficient to have no active selection than to have selected
everything.
</para><para>
After having deselected you can bring your selection back by choosing
<menuchoice><guimenu>Select</guimenu><guimenuitem>Reselect</guimenuitem>
</menuchoice>.
</para>
</sect1>
<sect1 id="selections-painting">
<title>Painting your selection</title>
<para>
As said above you can essentially paint your selection, and just like
when you paint normally you can choose to paint your selection freehand or
guided with rectangles, ellipses, &etc;. You also have the choice of different
paint tools like pen, brush, airbrush, &etc;. Choose the guide tool, and the
paint tool in the toolbox, and go ahead and <quote>paint</quote> your
selection.
</para><para>
The guide tools work just like you may be used to from other applications. So
holding down shift while drawing a rectangle or an ellipse still forces them to
be a square or a circle respectively.
</para>
<screenshot>
<screeninfo>Painting a selection</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="using-selections-1.png" format="PNG" />
</imageobject>
<textobject>
<phrase>Painting a selection</phrase>
</textobject>
<caption><para>Painting a selection</para></caption>
</mediaobject>
</screenshot>
<screenshot>
<screeninfo>Painting a selection</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="using-selections-2.png" format="PNG" />
</imageobject>
<textobject>
<phrase>Painting a selection</phrase>
</textobject>
<caption><para>Painting a selection</para></caption>
</mediaobject>
</screenshot>
</sect1>
<sect1 id="selections-unselecting">
<title>Unselecting</title>
<para>
All the selection paint tools have an option to add or subtract from the
selection. This means that you can use all your familiar tools to both select
and unselect. There is also a true selection eraser among the selection paint
tools.
</para>
<screenshot>
<screeninfo>Unselecting</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="using-selections-3.png" format="PNG" />
</imageobject>
<textobject>
<phrase>Unselecting</phrase>
</textobject>
<caption><para>Unselecting</para></caption>
</mediaobject>
</screenshot>
</sect1>
<sect1 id="selections-making-new">
<title>Making a new selection</title>
<para>
When you want to make a new selection, replacing the currently active one, you
first need to deselect the active selection. Choose
<menuchoice><guimenu>Select</guimenu><guimenuitem>Deselect</guimenuitem>
</menuchoice>.
</para>
</sect1>
<sect1 id="selections-contigious">
<title>Selecting a contiguous area (magic wand)</title>
<para>
To follow the analogy of painting your selection &chalk; also provides an
equivalent to filling a contiguous area. Some paint applications call this
selection tool the magic wand tool. What it does is select the nearby
pixels as long as they have nearly the same color as the pixel you click
on. The selection floods out from the point you click on. In the fuzziness
option you can set how different the colors are allowed to be before the
flooding stops.
</para>
<screenshot>
<screeninfo>Before the magic wand</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="using-selections-4.png" format="PNG" />
</imageobject>
<textobject>
<phrase>Before the magic wand</phrase>
</textobject>
<caption><para>Before the magic wand</para></caption>
</mediaobject>
</screenshot>
<screenshot>
<screeninfo>A magic wand selection</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="using-selections-5.png" format="PNG" />
</imageobject>
<textobject>
<phrase>A magic wand selection</phrase>
</textobject>
<caption><para>A magic wand selection</para></caption>
</mediaobject>
</screenshot>
</sect1>
<sect1 id="selections-similar">
<title>Selecting similar colors</title>
<para>
The <guilabel>Select Similar</guilabel> tool lets you pick a pixel and then select all pixels that
have a similar color. Picking a color in one corner of the image may select a
pixel in another corner if they have similar color.
With the <guilabel>Fuzziness</guilabel> option you can set how similar the colors must be to become
selected.
</para>
<screenshot>
<screeninfo>Selecting similar colors</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="using-selections-6.png" format="PNG" />
</imageobject>
<textobject>
<phrase>Selecting similar colors</phrase>
</textobject>
<caption><para>Selecting similar colors</para></caption>
</mediaobject>
</screenshot>
</sect1>
<sect1 id="selections-inverting">
<title>Inverting the selection</title>
<para>
In some cases it is easier to specify your selection the other way around. That
is, first you select the parts that ultimately should not be selected and then
then you choose
<menuchoice><guimenu>Select</guimenu><guimenuitem>Invert</guimenuitem>
</menuchoice>.
What invert does, is that for every pixel it flips the selection level so to
speak, by setting it to 256 minus the current selection level. Thus what was
selected becomes unselected and vice versa.
</para>
</sect1>
</chapter>
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