From e98469ecf6ad2b93afc1481e1ebb90bb5af3acc3 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Mon, 25 Jun 2018 21:08:41 +1000
Subject: [PATCH] Added transparency to matrix conversion

---
 Tests/test_image_convert.py |  3 +++
 src/PIL/Image.py            | 21 ++++++++++++++++++---
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/Tests/test_image_convert.py b/Tests/test_image_convert.py
index 1e208d80c..84c1cc82e 100644
--- a/Tests/test_image_convert.py
+++ b/Tests/test_image_convert.py
@@ -187,6 +187,7 @@ class TestImageConvert(PillowTestCase):
         def matrix_convert(mode):
             # Arrange
             im = hopper('RGB')
+            im.info['transparency'] = (255, 0, 0)
             matrix = (
                 0.412453, 0.357580, 0.180423, 0,
                 0.212671, 0.715160, 0.072169, 0,
@@ -203,9 +204,11 @@ class TestImageConvert(PillowTestCase):
             target = Image.open('Tests/images/hopper-XYZ.png')
             if converted_im.mode == 'RGB':
                 self.assert_image_similar(converted_im, target, 3)
+                self.assertEqual(converted_im.info['transparency'], (105, 54, 4))
             else:
                 self.assert_image_similar(converted_im,
                                           target.getchannel(0), 1)
+                self.assertEqual(converted_im.info['transparency'], 105)
 
         matrix_convert('RGB')
         matrix_convert('L')
diff --git a/src/PIL/Image.py b/src/PIL/Image.py
index f13a98276..e31d9002d 100644
--- a/src/PIL/Image.py
+++ b/src/PIL/Image.py
@@ -900,12 +900,28 @@ class Image(object):
         if not mode or (mode == self.mode and not matrix):
             return self.copy()
 
+        has_transparency = self.info.get('transparency') is not None
         if matrix:
             # matrix conversion
             if mode not in ("L", "RGB"):
                 raise ValueError("illegal conversion")
             im = self.im.convert_matrix(mode, matrix)
-            return self._new(im)
+            new = self._new(im)
+            if has_transparency and self.im.bands == 3:
+                transparency = new.info['transparency']
+
+                def convert_transparency(m, v):
+                    v = m[0]*v[0] + m[1]*v[1] + m[2]*v[2] + m[3]*0.5
+                    return max(0, min(255, int(v)))
+                if mode == "L":
+                    transparency = convert_transparency(matrix, transparency)
+                elif len(mode) == 3:
+                    transparency = tuple([
+                        convert_transparency(matrix[i*4:i*4+4], transparency)
+                        for i in range(0, len(transparency))
+                    ])
+                new.info['transparency'] = transparency
+            return new
 
         if mode == "P" and self.mode == "RGBA":
             return self.quantize(colors)
@@ -913,8 +929,7 @@ class Image(object):
         trns = None
         delete_trns = False
         # transparency handling
-        if "transparency" in self.info and \
-                self.info['transparency'] is not None:
+        if has_transparency:
             if self.mode in ('L', 'RGB') and mode == 'RGBA':
                 # Use transparent conversion to promote from transparent
                 # color to an alpha channel.