<chapter id="filters">
<title>Filters</title>

<para>
This chapter describes the various filters in detail. To illustrate the result
of applying the filters, each description is accompanied by an sample image
with the respective filter applied to it. The original image (with thanks to the
photographer, Christian Peper) is shown below at half of the original size. The
sample images demonstrating the results of applying the filters, are shown at
25% of the original size.
</para>
<note><para>Some filters yield reasonable results for most images. For
other filters though, quite some tweaking needs to be done before the desired
outcome is achieved. If a filter does not do what you want, it might need
more or less customising.</para></note>
<para>
See the <link linkend="commands-dialogs">Dialogs</link> chapter for more
information on the dialog windows containing the filter settings.
</para>

<screenshot>
<screeninfo>The original image.</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="crocusses.png" format="PNG" />
</imageobject>
<textobject>
<phrase>The original image.</phrase>
</textobject>
<caption><para>The original image.</para></caption>
</mediaobject>
</screenshot>

<sect1 id="filters-bumpmap">
<title>The Bumpmap filter</title>
<para>
The Bumpmap filter takes two layers and uses one of these to convert the other
one so that it will give an illusion of depth. The object layer (the layer to be
transformed) is the actual layer that should receive the three-dimensional
looks. The bumpmap layer is a grayscale layer, which is read and used to
determine the height for each point of the object layer.
</para><para>
Alternatively, the same layer can be used as both object layer and bumpmap
layer.
</para>
<screenshot>
<screeninfo>The image with the Bumpmap filter applied to it.</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="crocusses-bumpmap.png" format="PNG" />
</imageobject>
<textobject>
<phrase>The image with the Bumpmap filter applied to it.</phrase>
</textobject>
<caption><para>The image with the Bumpmap filter applied to it.</para></caption>
</mediaobject>
</screenshot>
</sect1>

<sect1 id="filters-edgedetection">
<title>The Edge Detection filters</title>
<para>
These filters try to detect <quote>edges</quote> (boundaries) in the picture
and modify the image such that only these edges retain their respective colors,
while the rest of the image is turned gray. Through the use of lighting the
image will then get a three-dimensional look.
</para><para>
There are four edge detection filters available. Each of these detects edges
from a different side (possibly considering other parts of the image as being
edges) and will therefore obtain a different resulting image.
</para>
<screenshot>
<screeninfo>The image with the Bottom Edge Detection filter applied to
it.</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="crocusses-edgebottom.png" format="PNG" />
</imageobject>
<textobject>
<phrase>The image with the Bottom Edge Detection filter applied to it.</phrase>
</textobject>
<caption><para>The image with the Bottom Edge Detection filter applied to
it.</para></caption>
</mediaobject>
</screenshot>
</sect1>

<sect1 id="filters-emboss">
<title>The Emboss filters</title>
<para>
Emboss filters work somewhat like edge detection filters, with the difference
that embossed images are entirely gray. Areas in the picture are detected and
are given a certain <quote>height level</quote>, which is made visible by using
grayscale borders, making the image look like it is three-dimensional.
</para>
<screenshot>
<screeninfo>The image with the Emboss All filter applied to it.</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="crocusses-embossall.png" format="PNG" />
</imageobject>
<textobject>
<phrase>The image with the Emboss All filter applied to it.</phrase>
</textobject>
<caption><para>The image with the Emboss All filter applied to
it.</para></caption>
</mediaobject>
</screenshot>
<screenshot>
<screeninfo>The image with the Emboss Variable filter applied to
it.</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="crocusses-embossvariable.png" format="PNG" />
</imageobject>
<textobject>
<phrase>The image with the Emboss Variable filter applied to it.</phrase>
</textobject>
<caption><para>The image with the Emboss Variable filter applied to
it.</para></caption>
</mediaobject>
</screenshot>
</sect1>

<sect1 id="filters-gaussianblur">
<title>The Gaussian Blur filter</title>
<para>
This filter makes the image a little fuzzy by blurring it in a pseudo-random
way. A gaussian algorithm is used for finding the extent to which each part of
the image should be blurred.
</para>
<screenshot>
<screeninfo>The image with the Gaussian Blur filter applied to it.</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="crocusses-gaussianblur.png" format="PNG" />
</imageobject>
<textobject>
<phrase>The image with the Gaussian Blur filter applied to it.</phrase>
</textobject>
<caption><para>The image with the Gaussian Blur filter applied to
it.</para></caption>
</mediaobject>
</screenshot>
</sect1>

<sect1 id="filters-invert">
<title>The Invert filter</title>
<para>
This filter inverts all colors. The Red, Green and Blue component of each pixel
are taken and subtracted from 255. This means that red becomes cyan, green
becomes purple, and blue becomes yellow. The resulting values form the new
pixel color.
</para>
<screenshot>
<screeninfo>The image with the Invert filter applied to it.</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="crocusses-invert.png" format="PNG" />
</imageobject>
<textobject>
<phrase>The image with the Invert filter applied to it.</phrase>
</textobject>
<caption><para>The image with the Invert filter applied to it.</para></caption>
</mediaobject>
</screenshot>
</sect1>

<sect1 id="filters-meanremoval">
<title>The Mean Removal filter</title>
<para>
This filter sharpens the image by changing the colors of neighboring pixels
with approximately the same color, so that small differences are evened out.
</para>
<screenshot>
<screeninfo>The image with the Mean Removal filter applied to it.</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="crocusses-meanremoval.png" format="PNG" />
</imageobject>
<textobject>
<phrase>The image with the Mean Removal filter applied to it.</phrase>
</textobject>
<caption><para>The image with the Mean Removal filter applied to
it.</para></caption>
</mediaobject>
</screenshot>
</sect1>

<sect1 id="filters-oilpaint">
<title>The Oilpaint filter</title>
<para>
An oilpaint effect is given to the image by creating patch-shaped areas in which
the most important color is applied to the entire area.
</para>
<screenshot>
<screeninfo>The image with the Oilpaint filter applied to it.</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="crocusses-oilpaint.png" format="PNG" />
</imageobject>
<textobject>
<phrase>The image with the Oilpaint filter applied to it.</phrase>
</textobject>
<caption><para>The image with the Oilpaint filter applied to
it.</para></caption>
</mediaobject>
</screenshot>
</sect1>

<sect1 id="filters-pixelize">
<title>The Pixelize filter</title>
<para>
The image is pixelated by taking a square area and giving it the mean color
value of the pixels it contains.
</para>
<screenshot>
<screeninfo>The image with the Pixelize filter applied to it.</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="crocusses-pixelize.png" format="PNG" />
</imageobject>
<textobject>
<phrase>The image with the Pixelize filter applied to it.</phrase>
</textobject>
<caption><para>The image with the Pixelize filter applied to
it.</para></caption>
</mediaobject>
</screenshot>
</sect1>

<sect1 id="filters-raindrops">
<title>The Raindrops filter</title>
<para>
This filter makes it look like raindrops have fallen on the image by distorting
drop-shaped areas with a lens-like effect as one would see when looking
at the image through a real raindrop. Some raindrops will have a fish-eye lens
effect.
</para>
<screenshot>
<screeninfo>The image with the Raindrops filter applied to it.</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="crocusses-raindrops.png" format="PNG" />
</imageobject>
<textobject>
<phrase>The image with the Raindrops filter applied to it.</phrase>
</textobject>
<caption><para>The image with the Raindrops filter applied to
it.</para></caption>
</mediaobject>
</screenshot>
</sect1>

<sect1 id="filters-roundcorners">
<title>The Round Corners filter</title>
<para>
This filter just rounds off the corners of the image. This is done by making
the outside of the rounded corner transparent.
</para>
<screenshot>
<screeninfo>The image with the Round Corners filter applied to it.</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="crocusses-roundcorners.png" format="PNG" />
</imageobject>
<textobject>
<phrase>The image with the Round Corners filter applied to it.</phrase>
</textobject>
<caption><para>The image with the Round Corners filter applied to
it.</para></caption>
</mediaobject>
</screenshot>
</sect1>

<sect1 id="filters-sharpen">
<title>The Sharpen filter</title>
<para>
This filter sharpens the image.
</para>
<screenshot>
<screeninfo>The image with the Sharpen filter applied to it.</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="crocusses-sharpen.png" format="PNG" />
</imageobject>
<textobject>
<phrase>The image with the Sharpen filter applied to it.</phrase>
</textobject>
<caption><para>The image with the Sharpen filter applied to it.</para></caption>
</mediaobject>
</screenshot>
</sect1>

<sect1 id="filters-simplenoise">
<title>The Simple Noise Reduction filter</title>
<para>
This filter reduces noise in the image by giving loose pixels a color close to
the surrounding area. This causes small details to be lost, but can enhance the
general view of the image when this is hampered by too many unnecessary details.
</para>
<screenshot>
<screeninfo>The image with the Simple Noise Reduction filter applied to
it.</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="crocusses-simplenoise.png" format="PNG" />
</imageobject>
<textobject>
<phrase>The image with the Simple Noise Reduction filter applied to it.</phrase>
</textobject>
<caption><para>The image with the Simple Noise Reduction filter applied to
it.</para></caption>
</mediaobject>
</screenshot>
</sect1>

<sect1 id="filters-tiles">
<title>The Small Tiles filter</title>
<para>
The picture is reduced in size and repeated multiple times.
</para>
<screenshot>
<screeninfo>The image with the Small Tiles filter applied to it.</screeninfo>
<mediaobject>
<imageobject>
<imagedata fileref="crocusses-tiles.png" format="PNG" />
</imageobject>
<textobject>
<phrase>The image with the Small Tiles filter applied to it.</phrase>
</textobject>
<caption><para>The image with the Small Tiles filter applied to
it.</para></caption>
</mediaobject>
</screenshot>
</sect1>

</chapter>
