From d05f5d8047d2013ebf2d672dd8516c541909e0a3 Mon Sep 17 00:00:00 2001
From: Tony Cook <tony@develop-help.com>
Date: Fri, 13 Jul 2012 19:53:44 +1000
Subject: [PATCH] add a recipe to the cookbook

it's been a while, and the intuition was interesting
---
 lib/Imager/Cookbook.pod | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/lib/Imager/Cookbook.pod b/lib/Imager/Cookbook.pod
index 9fcf6f29..ad7af17e 100644
--- a/lib/Imager/Cookbook.pod
+++ b/lib/Imager/Cookbook.pod
@@ -432,6 +432,23 @@ in pixels per centimeter, you would do:
 
 Keywords: DPI
 
+=head1 IMAGE MANIPULATION
+
+=head2 Replacing a color with transparency
+X<replacing colors>
+
+To replace a color with transparency you can use the
+L<Imager::Filters/difference()> method.
+
+  # make a work image the same size as our input
+  my $work = Imager->new(xsize => $in->getwidth, ysize => $in->getheight,
+                         channels => $in->getchannels);
+  # and fill it with the colour we want transparent
+  $work->box(filled => 1, color => $color);
+
+  # get an image with that colour replaced with transparent black
+  my $out = $work->difference(other => $in);
+
 =head1 AUTHOR
 
 Tony Cook <tony@develop-help.com>
-- 
2.39.5