From a64ef19e39a7cbb13b5ec2fbe07aa32133911f8d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?R=C3=A9gis=20Hanol?= <regis@hanol.fr>
Date: Thu, 1 Jun 2017 23:10:36 +0200
Subject: [PATCH] FIX: automatic PNG-to-JPEG conversion should use a default
 white background

---
 lib/upload_creator.rb | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/upload_creator.rb b/lib/upload_creator.rb
index c47afd4a1f4..1a9b5774205 100644
--- a/lib/upload_creator.rb
+++ b/lib/upload_creator.rb
@@ -132,7 +132,13 @@ class UploadCreator
     jpeg_tempfile = Tempfile.new(["image", ".jpg"])
 
     OptimizedImage.ensure_safe_paths!(@file.path, jpeg_tempfile.path)
-    Discourse::Utils.execute_command('convert', @file.path, '-quality', SiteSetting.png_to_jpg_quality.to_s, jpeg_tempfile.path)
+    Discourse::Utils.execute_command(
+      'convert', @file.path,
+      '-background', 'white',
+      '-flatten',
+      '-quality', SiteSetting.png_to_jpg_quality.to_s,
+      jpeg_tempfile.path
+    )
 
     # keep the JPEG if it's at least 15% smaller
     if File.size(jpeg_tempfile.path) < filesize * 0.85