From 838a5cffe77c645e7f77b4228a4db26e7f546cf5 Mon Sep 17 00:00:00 2001
From: Alexander <homm86@gmail.com>
Date: Mon, 26 Mar 2018 23:17:17 +0300
Subject: [PATCH] more tests and fixed bug for interpolate4

---
 Tests/test_color_lut.py   | 21 +++++++++++++++++++++
 src/libImaging/ColorLUT.c |  2 +-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/Tests/test_color_lut.py b/Tests/test_color_lut.py
index 2da59b115..65b5c5127 100644
--- a/Tests/test_color_lut.py
+++ b/Tests/test_color_lut.py
@@ -146,6 +146,27 @@ class TestColorLut3DCoreAPI(PillowTestCase):
             im.im.color_lut_3d('RGB', Image.LINEAR,
                 *self.generate_unit_table(3, (2, 2, 65)))))
 
+    def test_units_4channels(self):
+        g = Image.linear_gradient('L')
+        im = Image.merge('RGB', [g, g.transpose(Image.ROTATE_90),
+                                 g.transpose(Image.ROTATE_180)])
+
+        # Red channel copied to alpha
+        self.assert_image_equal(
+            Image.merge('RGBA', (im.split()*2)[:4]),
+            im._new(im.im.color_lut_3d('RGBA', Image.LINEAR,
+                *self.generate_unit_table(4, 17))))
+
+    def test_copy_alpha_channel(self):
+        g = Image.linear_gradient('L')
+        im = Image.merge('RGBA', [g, g.transpose(Image.ROTATE_90),
+                                  g.transpose(Image.ROTATE_180),
+                                  g.transpose(Image.ROTATE_270)])
+
+        self.assert_image_equal(im, im._new(
+            im.im.color_lut_3d('RGBA', Image.LINEAR,
+                *self.generate_unit_table(3, 17))))
+
     def test_channels_order(self):
         g = Image.linear_gradient('L')
         im = Image.merge('RGB', [g, g.transpose(Image.ROTATE_90),
diff --git a/src/libImaging/ColorLUT.c b/src/libImaging/ColorLUT.c
index f9dd91cb8..3f930c3ee 100644
--- a/src/libImaging/ColorLUT.c
+++ b/src/libImaging/ColorLUT.c
@@ -111,7 +111,7 @@ ImagingColorLUT3D_linear(Imaging imOut, Imaging imIn, int table_channels,
             INT16 shift1D = (SCALE_MASK & index1D) >> (SCALE_BITS - SHIFT_BITS);
             INT16 shift2D = (SCALE_MASK & index2D) >> (SCALE_BITS - SHIFT_BITS);
             INT16 shift3D = (SCALE_MASK & index3D) >> (SCALE_BITS - SHIFT_BITS);
-            int idx = 3 * table_index3D(
+            int idx = table_channels * table_index3D(
                 index1D >> SCALE_BITS, index2D >> SCALE_BITS,
                 index3D >> SCALE_BITS, size1D, size1D_2D);
             INT16 result[4], left[4], right[4];