From 4cfdb3c09571c22206ca38f652283be7180f8636 Mon Sep 17 00:00:00 2001
From: Glenn Randers-Pehrson <glennrp at users.sourceforge.net>
Date: Thu, 26 Nov 2009 11:49:37 -0600
Subject: [PATCH] [devel] Add comment about TODO: issue warning if user tries
 to premultiply

in a nonliner colorspace.
---
 pngread.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/pngread.c b/pngread.c
index 0afec895d..96b844f07 100644
--- a/pngread.c
+++ b/pngread.c
@@ -425,6 +425,24 @@ png_read_update_info(png_structp png_ptr, png_infop info_ptr)
    else
       png_warning(png_ptr,
       "Ignoring extra png_read_update_info() call; row buffer not reallocated");
+
+#ifdef PNG_READ_PREMULTIPLY_ALPHA_SUPPORTED
+   if (png_ptr->transformations & PNG_PREMULTIPLY_ALPHA)
+   {
+     /* TO DO:
+      * Check for linear colorspace and if not, issue a warning.
+      * If gAMA is present with gamma == 1.0, it's linear.
+      * If iCCP is present, assume user knows what they are doing
+      *   and it's linear.
+      * If gAMA is present with gamma != 1.0, it's not linear.
+      * If no gAMA or iCCP, assume not linear.
+      * If not linear do:
+      *   png_warning(png_ptr,
+      *      "Premultiply should only be used with gamma == 1.0");
+      */
+   }
+#endif
+
    png_read_transform_info(png_ptr, info_ptr);
 }