Testing for p2la

Tests/test_image_convert.py

@@ -123,6 +123,26 @@ class TestImageConvert(PillowTestCase):
         self.assertNotIn('transparency', p.info)
         p.save(f)
 
+    # ref https://github.com/python-pillow/Pillow/issues/1979
+
+    def test_p_la(self):
+        def L(rgb):
+            return int((rgb[0] * 299 + rgb[1] * 587 + rgb[2] * 114) / 1000)
+
+        def convert_to_gray(im, pixel):
+            if im.mode == 'P':
+                color_id = im.getpixel(pixel)
+                color = im.getpalette()[color_id * 3:(color_id+1)*3]
+                return L(color)
+            elif im.mode == 'LA':
+                color = im.getpixel(pixel)
+                return color[0]
+
+        im_p = hopper('P')
+        im_la = im_p.convert('LA')
+        self.assertEqual(convert_to_gray(im_p, (5, 5)),
+                         convert_to_gray(im_la, (5, 5)))
+
 
 if __name__ == '__main__':
     unittest.main()