From e24b13ad4f2efcea02397651e22210de8e7065b4 Mon Sep 17 00:00:00 2001
From: Christoph Michael Becker <cmb@php.net>
Date: Sun, 27 Aug 2017 12:45:43 +0000
Subject: [PATCH] Improve IMG_FILTER_GRAYSCALE documentation

git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@342945 c90b9560-bf6c-de11-be94-00142212c4b1
---
 reference/image/functions/imagefilter.xml | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/reference/image/functions/imagefilter.xml b/reference/image/functions/imagefilter.xml
index 04bc634593..1dd142f3bc 100644
--- a/reference/image/functions/imagefilter.xml
+++ b/reference/image/functions/imagefilter.xml
@@ -41,7 +41,10 @@
         <listitem>
          <simpara>
           <constant>IMG_FILTER_GRAYSCALE</constant>: Converts the image into
-          grayscale.
+          grayscale by changing the red, green and blue components to their
+          weighted sum using the same coefficients as the REC.601 luma (Y')
+          calculation. The alpha components are retained. For palette images the
+          result may differ due to palette limitations.
          </simpara>
         </listitem>
         <listitem>