Added transparency for all PNG greyscale modes

Tests/test_file_png.py

@@ -291,30 +291,32 @@ class TestFilePng(PillowTestCase):
         self.assert_image(im, "RGBA", (10, 10))
         self.assertEqual(im.getcolors(), [(100, (0, 0, 0, 0))])
 
-    def test_save_l_transparency(self):
-        # There are 559 transparent pixels in l_trns.png.
-        num_transparent = 559
+    def test_save_greyscale_transparency(self):
+        for mode, num_transparent in {
+            "1": 1994,
+            "L": 559,
+            "I": 559,
+        }.items():
+            in_file = "Tests/images/"+mode.lower()+"_trns.png"
+            im = Image.open(in_file)
+            self.assertEqual(im.mode, mode)
+            self.assertEqual(im.info["transparency"], 255)
 
-        in_file = "Tests/images/l_trns.png"
-        im = Image.open(in_file)
-        self.assertEqual(im.mode, "L")
-        self.assertEqual(im.info["transparency"], 255)
+            im_rgba = im.convert('RGBA')
+            self.assertEqual(
+                im_rgba.getchannel("A").getcolors()[0][0], num_transparent)
 
-        im_rgba = im.convert('RGBA')
-        self.assertEqual(
-            im_rgba.getchannel("A").getcolors()[0][0], num_transparent)
+            test_file = self.tempfile("temp.png")
+            im.save(test_file)
 
-        test_file = self.tempfile("temp.png")
-        im.save(test_file)
+            test_im = Image.open(test_file)
+            self.assertEqual(test_im.mode, mode)
+            self.assertEqual(test_im.info["transparency"], 255)
+            self.assert_image_equal(im, test_im)
 
-        test_im = Image.open(test_file)
-        self.assertEqual(test_im.mode, "L")
-        self.assertEqual(test_im.info["transparency"], 255)
-        self.assert_image_equal(im, test_im)
-
-        test_im_rgba = test_im.convert('RGBA')
-        self.assertEqual(
-            test_im_rgba.getchannel('A').getcolors()[0][0], num_transparent)
+            test_im_rgba = test_im.convert('RGBA')
+            self.assertEqual(
+                test_im_rgba.getchannel('A').getcolors()[0][0], num_transparent)
 
     def test_save_rgb_single_transparency(self):
         in_file = "Tests/images/caption_6_33_22.png"

docs/handbook/image-file-formats.rst

@@ -490,12 +490,12 @@ The :py:meth:`~PIL.Image.Image.open` method sets the following
     For ``P`` images: Either the palette index for full transparent pixels,
     or a byte string with alpha values for each palette entry.
 
-    For ``L`` and ``RGB`` images, the color that represents full transparent
-    pixels in this image.
+    For ``1``, ``L``, ``I`` and ``RGB`` images, the color that represents
+    full transparent pixels in this image.
 
     This key is omitted if the image is not a transparent palette image.
 
-``Open`` also sets ``Image.text`` to a dictionary of the values of the
+``open`` also sets ``Image.text`` to a dictionary of the values of the
 ``tEXt``, ``zTXt``, and ``iTXt`` chunks of the PNG image. Individual
 compressed chunks are limited to a decompressed size of
 ``PngImagePlugin.MAX_TEXT_CHUNK``, by default 1MB, to prevent
@@ -511,8 +511,8 @@ The :py:meth:`~PIL.Image.Image.save` method supports the following options:
     encoder settings.
 
 **transparency**
-    For ``P``, ``L``, and ``RGB`` images, this option controls what
-    color image to mark as transparent.
+    For ``P``, ``1``, ``L``, ``I``, and ``RGB`` images, this option controls
+    what color from the image to mark as transparent.
 
     For ``P`` images, this can be a either the palette index,
     or a byte string with alpha values for each palette entry.

src/PIL/Image.py

@@ -950,7 +950,7 @@ class Image(object):
         delete_trns = False
         # transparency handling
         if has_transparency:
-            if self.mode in ('L', 'RGB') and mode == 'RGBA':
+            if self.mode in ('1', 'L', 'I', 'RGB') and mode == 'RGBA':
                 # Use transparent conversion to promote from transparent
                 # color to an alpha channel.
                 new_im = self._new(self.im.convert_transparent(

src/PIL/PngImagePlugin.py

@@ -54,19 +54,24 @@ _MAGIC = b"\211PNG\r\n\032\n"
 
 _MODES = {
     # supported bits/color combinations, and corresponding modes/rawmodes
+    # Greyscale
     (1, 0):  ("1", "1"),
     (2, 0):  ("L", "L;2"),
     (4, 0):  ("L", "L;4"),
     (8, 0):  ("L", "L"),
     (16, 0): ("I", "I;16B"),
+    # Truecolour
     (8, 2):  ("RGB", "RGB"),
     (16, 2): ("RGB", "RGB;16B"),
+    # Indexed-colour
     (1, 3):  ("P", "P;1"),
     (2, 3):  ("P", "P;2"),
     (4, 3):  ("P", "P;4"),
     (8, 3):  ("P", "P"),
+    # Greyscale with alpha
     (8, 4):  ("LA", "LA"),
     (16, 4): ("RGBA", "LA;16B"),  # LA;16B->LA not yet available
+    # Truecolour with alpha
     (8, 6):  ("RGBA", "RGBA"),
     (16, 6): ("RGBA", "RGBA;16B"),
 }
@@ -386,7 +391,7 @@ class PngStream(ChunkStream):
                 # otherwise, we have a byte string with one alpha value
                 # for each palette entry
                 self.im_info["transparency"] = s
-        elif self.im_mode == "L":
+        elif self.im_mode in ("1", "L", "I"):
             self.im_info["transparency"] = i16(s)
         elif self.im_mode == "RGB":
             self.im_info["transparency"] = i16(s), i16(s[2:]), i16(s[4:])
@@ -841,7 +846,7 @@ def _save(im, fp, filename, chunk=putchunk):
                 transparency = max(0, min(255, transparency))
                 alpha = b'\xFF' * transparency + b'\0'
                 chunk(fp, b"tRNS", alpha[:alpha_bytes])
-        elif im.mode == "L":
+        elif im.mode in ("1", "L", "I"):
             transparency = max(0, min(65535, transparency))
             chunk(fp, b"tRNS", o16(transparency))
         elif im.mode == "RGB":

src/libImaging/Convert.c

@@ -592,6 +592,22 @@ i2f(UINT8* out_, const UINT8* in_, int xsize)
         *out++ = (FLOAT32) *in++;
 }
 
+static void
+i2rgb(UINT8* out, const UINT8* in_, int xsize)
+{
+    int x;
+    INT32* in = (INT32*) in_;
+    for (x = 0; x < xsize; x++, in++, out+=4) {
+        if (*in <= 0)
+            out[0] = out[1] = out[2] = 0;
+        else if (*in >= 255)
+            out[0] = out[1] = out[2] = 255;
+        else
+            out[0] = out[1] = out[2] = (UINT8) *in;
+        out[3] = 255;
+    }
+}
+
 /* ------------- */
 /* F conversions */
 /* ------------- */
@@ -807,11 +823,14 @@ static struct {
 
     { "La", "LA", la2lA },
 
-    { "I",    "L",    i2l },
-    { "I",    "F",    i2f },
+    { "I", "L", i2l },
+    { "I", "F", i2f },
+    { "I", "RGB", i2rgb },
+    { "I", "RGBA", i2rgb },
+    { "I", "RGBX", i2rgb },
 
-    { "F",    "L",    f2l },
-    { "F",    "I",    f2i },
+    { "F", "L", f2l },
+    { "F", "I", f2i },
 
     { "RGB", "1", rgb2bit },
     { "RGB", "L", rgb2l },
@@ -1385,6 +1404,8 @@ ImagingConvertTransparent(Imaging imIn, const char *mode,
     }
 
     if (!((strcmp(imIn->mode, "RGB") == 0 ||
+           strcmp(imIn->mode, "1") == 0 ||
+           strcmp(imIn->mode, "I") == 0 ||
            strcmp(imIn->mode, "L") == 0)
           && strcmp(mode, "RGBA") == 0))
 #ifdef notdef
@@ -1403,7 +1424,13 @@ ImagingConvertTransparent(Imaging imIn, const char *mode,
     if (strcmp(imIn->mode, "RGB") == 0) {
         convert = rgb2rgba;
     } else {
-        convert = l2rgb;
+        if (strcmp(imIn->mode, "1") == 0) {
+            convert = bit2rgb;
+        } else if (strcmp(imIn->mode, "I") == 0) {
+            convert = i2rgb;
+        } else {
+            convert = l2rgb;
+        }
         g = b = r;
     }