Fixed loading L mode GIF with transparency

Tests/test_file_gif.py

@@ -59,6 +59,17 @@ def test_invalid_file():
         GifImagePlugin.GifImageFile(invalid_file)
 
 
+def test_l_mode_transparency():
+    with Image.open("Tests/images/no_palette_with_transparency.gif") as im:
+        assert im.mode == "L"
+        assert im.load()[0, 0] == 0
+        assert im.info["transparency"] == 255
+
+        im.seek(1)
+        assert im.mode == "LA"
+        assert im.load()[0, 0] == (0, 255)
+
+
 def test_optimize():
     def test_grayscale(optimize):
         im = Image.new("L", (1, 1), 0)

Tests/test_image_convert.py

@@ -135,6 +135,10 @@ def test_trns_l(tmp_path):
 
     f = str(tmp_path / "temp.png")
 
+    im_la = im.convert("LA")
+    assert "transparency" not in im_la.info
+    im_la.save(f)
+
     im_rgb = im.convert("RGB")
     assert im_rgb.info["transparency"] == (128, 128, 128)  # undone
     im_rgb.save(f)

Tests/test_image_paste.py

@@ -67,6 +67,16 @@ def gradient_RGB(self):
             ],
         )
 
+    @cached_property
+    def gradient_LA(self):
+        return Image.merge(
+            "LA",
+            [
+                self.gradient_L,
+                self.gradient_L.transpose(Image.Transpose.ROTATE_90),
+            ],
+        )
+
     @cached_property
     def gradient_RGBA(self):
         return Image.merge(
@@ -145,6 +155,28 @@ def test_image_mask_L(self):
                 ],
             )
 
+    def test_image_mask_LA(self):
+        for mode in ("RGBA", "RGB", "L"):
+            im = Image.new(mode, (200, 200), "white")
+            im2 = getattr(self, "gradient_" + mode)
+
+            self.assert_9points_paste(
+                im,
+                im2,
+                self.gradient_LA,
+                [
+                    (128, 191, 255, 191),
+                    (112, 207, 206, 111),
+                    (128, 254, 128, 1),
+                    (208, 208, 239, 239),
+                    (192, 191, 191, 191),
+                    (207, 207, 112, 113),
+                    (255, 255, 255, 255),
+                    (239, 207, 207, 239),
+                    (255, 191, 128, 191),
+                ],
+            )
+
     def test_image_mask_RGBA(self):
         for mode in ("RGBA", "RGB", "L"):
             im = Image.new(mode, (200, 200), "white")

src/PIL/GifImagePlugin.py

@@ -167,9 +167,15 @@ def _seek(self, frame):
         if self.__frame == 1:
             self.pyaccess = None
             if "transparency" in self.info:
-                self.mode = "RGBA"
-                self.im.putpalettealpha(self.info["transparency"], 0)
-                self.im = self.im.convert("RGBA", Image.Dither.FLOYDSTEINBERG)
+                if self.mode == "P":
+                    self.im.putpalettealpha(self.info["transparency"], 0)
+                    self.im = self.im.convert("RGBA", Image.Dither.FLOYDSTEINBERG)
+                    self.mode = "RGBA"
+                else:
+                    self.im = self.im.convert_transparent(
+                        "LA", self.info["transparency"]
+                    )
+                    self.mode = "LA"
 
                 del self.info["transparency"]
             else:
@@ -368,15 +374,18 @@ def load_end(self):
         if self.__frame == 0:
             return
         if self._frame_transparency is not None:
-            self.im.putpalettealpha(self._frame_transparency, 0)
-            frame_im = self.im.convert("RGBA")
+            if self.mode == "P":
+                self.im.putpalettealpha(self._frame_transparency, 0)
+                frame_im = self.im.convert("RGBA")
+            else:
+                frame_im = self.im.convert_transparent("LA", self._frame_transparency)
         else:
             frame_im = self.im.convert("RGB")
         frame_im = self._crop(frame_im, self.dispose_extent)
 
         self.im = self._prev_im
         self.mode = self.im.mode
-        if frame_im.mode == "RGBA":
+        if frame_im.mode in ("LA", "RGBA"):
             self.im.paste(frame_im, self.dispose_extent, frame_im)
         else:
             self.im.paste(frame_im, self.dispose_extent)

src/PIL/Image.py

@@ -975,7 +975,9 @@ def convert_transparency(m, v):
         delete_trns = False
         # transparency handling
         if has_transparency:
-            if self.mode in ("1", "L", "I", "RGB") and mode == "RGBA":
+            if (self.mode in ("1", "L", "I") and mode in ("LA", "RGBA")) or (
+                self.mode == "RGB" and mode == "RGBA"
+            ):
                 # Use transparent conversion to promote from transparent
                 # color to an alpha channel.
                 new_im = self._new(
@@ -1564,8 +1566,8 @@ def paste(self, im, box=None, mask=None):
         also use color strings as supported by the ImageColor module.
 
         If a mask is given, this method updates only the regions
-        indicated by the mask.  You can use either "1", "L" or "RGBA"
-        images (in the latter case, the alpha band is used as mask).
+        indicated by the mask. You can use either "1", "L", "LA", "RGBA"
+        or "RGBa" images (if present, the alpha band is used as mask).
         Where the mask is 255, the given image is copied as is.  Where
         the mask is 0, the current value is preserved.  Intermediate
         values will mix the two images together, including their alpha
@@ -1613,7 +1615,7 @@ def paste(self, im, box=None, mask=None):
         elif isImageType(im):
             im.load()
             if self.mode != im.mode:
-                if self.mode != "RGB" or im.mode not in ("RGBA", "RGBa"):
+                if self.mode != "RGB" or im.mode not in ("LA", "RGBA", "RGBa"):
                     # should use an adapter for this!
                     im = im.convert(self.mode)
             im = im.im

src/libImaging/Convert.c

@@ -1634,29 +1634,15 @@ ImagingConvertTransparent(Imaging imIn, const char *mode, int r, int g, int b) {
         return (Imaging)ImagingError_ModeError();
     }
 
-    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
-    {
-        return (Imaging)ImagingError_ValueError("conversion not supported");
-    }
-#else
-    {
-        static char buf[100];
-        snprintf(
-            buf,
-            100,
-            "conversion from %.10s to %.10s not supported in convert_transparent",
-            imIn->mode,
-            mode);
-        return (Imaging)ImagingError_ValueError(buf);
-    }
-#endif
-
-    if (strcmp(imIn->mode, "RGB") == 0) {
+    if (strcmp(imIn->mode, "RGB") == 0 && strcmp(mode, "RGBA") == 0) {
         convert = rgb2rgba;
-    } else {
+    } else if ((strcmp(imIn->mode, "1") == 0 ||
+                strcmp(imIn->mode, "I") == 0 ||
+                strcmp(imIn->mode, "L") == 0
+               ) && (
+                strcmp(mode, "RGBA") == 0 ||
+                strcmp(mode, "LA") == 0
+               )) {
         if (strcmp(imIn->mode, "1") == 0) {
             convert = bit2rgb;
         } else if (strcmp(imIn->mode, "I") == 0) {
@@ -1665,6 +1651,15 @@ ImagingConvertTransparent(Imaging imIn, const char *mode, int r, int g, int b) {
             convert = l2rgb;
         }
         g = b = r;
+    } else {
+        static char buf[100];
+        snprintf(
+            buf,
+            100,
+            "conversion from %.10s to %.10s not supported in convert_transparent",
+            imIn->mode,
+            mode);
+        return (Imaging)ImagingError_ValueError(buf);
     }
 
     imOut = ImagingNew2Dirty(mode, imOut, imIn);

src/libImaging/Paste.c

@@ -295,7 +295,7 @@ ImagingPaste(
         paste_mask_L(imOut, imIn, imMask, dx0, dy0, sx0, sy0, xsize, ysize, pixelsize);
         ImagingSectionLeave(&cookie);
 
-    } else if (strcmp(imMask->mode, "RGBA") == 0) {
+    } else if (strcmp(imMask->mode, "LA") == 0 || strcmp(imMask->mode, "RGBA") == 0) {
         ImagingSectionEnter(&cookie);
         paste_mask_RGBA(
             imOut, imIn, imMask, dx0, dy0, sx0, sy0, xsize, ysize, pixelsize);