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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 1.3 $ -->
<chapter xml:id="image.examples" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
&reftitle.examples;
<section xml:id="image.examples-png">
<para>
<example>
<title>PNG creation with PHP</title>
<programlisting role="php">
<![CDATA[
<?php
header("Content-type: image/png");
$string = $_GET['text'];
$im = imagecreatefrompng("images/button1.png");
$orange = imagecolorallocate($im, 220, 210, 60);
$px = (imagesx($im) - 7.5 * strlen($string)) / 2;
imagestring($im, 3, $px, 9, $string, $orange);
imagepng($im);
imagedestroy($im);
?>
]]>
</programlisting>
</example>
This example would be called from a page with a tag like: <img
src="button.php?text=text">. The above button.php script
then takes this "text" string and overlays it on top of a
base image which in this case is "images/button1.png"
and outputs the resulting image. This is a very convenient way to
avoid having to draw new button images every time you want to
change the text of a button. With this method they are
dynamically generated.
</para>
</section>
<section xml:id="image.examples-watermark">
<para>
<example>
<title>Adding watermarks to images using alpha channels</title>
<programlisting role="php">
<![CDATA[
<?php
// Load the stamp and the photo to apply the watermark to
$stamp = imagecreatefrompng('stamp.png');
$im = imagecreatefromjpeg('photo.jpeg');
// Set the margins for the stamp and get the height/width of the stamp image
$marge_right = 10;
$marge_bottom = 10;
$sx = imagesx($stamp);
$sy = imagesy($stamp);
// Copy the stamp image onto our photo using the margin offsets and the photo
// width to calculate positioning of the stamp.
imagecopy($im, $stamp, imagesx($im) - $sx - $marge_right, imagesy($im) - $sy - $marge_bottom, 0, 0, imagesx($stamp), imagesy($stamp));
// Output and free memory
header('Content-type: image/png');
imagepng($im);
imagedestroy($im);
?>
]]>
</programlisting>
<mediaobject>
<imageobject>
<imagedata fileref="figures/image.watermarks.png" />
</imageobject>
</mediaobject>
</example>
This example is a common way to add watermarks and stamps to photos and
copyrighted images. Note that the presence of an alpha channel in the
stamp image as the text is anti-aliased. This is preserved during copying.
</para>
</section>
<section xml:id="image.examples.merged-watermark">
<para>
<example>
<title>Using <function>imagecopymerge</function> to create a translucent watermark</title>
<programlisting role="php">
<![CDATA[
<?php
// Load the stamp and the photo to apply the watermark to
$im = imagecreatefromjpeg('photo.jpeg');
// First we create our stamp image manually from GD
$stamp = imagecreatetruecolor(100, 70);
imagefilledrectangle($stamp, 0,0, 99, 99, 0x0000FF);
imagefilledrectangle($stamp, 9,9, 90,60, 0xFFFFFF);
$im = imagecreatefromjpeg('photo.jpeg');
imagestring($stamp, 5, 20, 20, 'libGD', 0x0000FF);
imagestring($stamp, 3, 20, 40, '(c) 2007-8', 0x0000FF);
// Set the margins for the stamp and get the height/width of the stamp image
$marge_right = 10;
$marge_bottom = 10;
$sx = imagesx($stamp);
$sy = imagesy($stamp);
// Merge the stamp onto our photo with an opacity (transparency) of 50%
imagecopymerge($im, $stamp, imagesx($im) - $sx - $marge_right, imagesy($im) - $sy - $marge_bottom, 0, 0, imagesx($stamp), imagesy($stamp), 50);
// Save the image to file and free memory
imagepng($im, 'photo_stamp.png');
imagedestroy($im);
?>
]]>
</programlisting>
<mediaobject>
<imageobject>
<imagedata fileref="figures/image.watermark-merged.png" />
</imageobject>
</mediaobject>
</example>
This example uses <function>imagecopymerge</function> to merge the stamp
with our original image. Using this we can set the opacity of our stamp -
in our example we've set it to 50% opacity (another term for transparency).
In practice this would be useful in copyright protection as semi-transparent
watermarks are hard to remove yet allow viewers to see the image.
</para>
</section>
</chapter>
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