Added support for Windows 1.0 icons

Tests/test_file_ico.py

@@ -227,3 +227,31 @@ def test_draw_reloaded(tmp_path):
 
     with Image.open(outfile) as im:
         assert_image_equal_tofile(im, "Tests/images/hopper_draw.ico")
+
+
+def test_ico1_open():
+    with Image.open("Tests/images/ico1.ico") as im:
+        assert_image_equal_tofile(im, "Tests/images/ico1.png")
+
+    with open("Tests/images/flower.jpg", "rb") as fp:
+        with pytest.raises(SyntaxError):
+            IcoImagePlugin.Ico1ImageFile(fp)
+
+
+def test_ico1_save(tmp_path):
+    outfile = str(tmp_path / "temp.ico")
+    with Image.open("Tests/images/l_trns.png") as im:
+        l_channel = im.convert("1").convert("L")
+        a_channel = im.convert("LA").getchannel("A")
+    la = Image.merge("LA", (l_channel, a_channel))
+
+    la.save(outfile, "ICO1")
+
+    with Image.open(outfile) as im:
+        assert_image_equal(im, la)
+
+    # Test saving in an incorrect mode
+    output = io.BytesIO()
+    im = hopper()
+    with pytest.raises(OSError):
+        im.save(output, "ICO1")

docs/handbook/image-file-formats.rst

@@ -342,6 +342,23 @@ The :py:meth:`~PIL.Image.Image.save` method can take the following keyword argum
 
     .. versionadded:: 8.3.0
 
+ICO1
+^^^^
+
+Pillow also reads and writes device-independent Windows 1.0 icons.
+
+.. versionadded:: 10.1.0
+
+.. _ico1-saving:
+
+Saving
+~~~~~~
+
+Since the .ico extension is already used for the ICO format, when saving a
+Windows 1.0 icon the output format must be specified explicitly::
+
+    im.save("newimage.ico", format="ICO1")
+
 IM
 ^^
 
@@ -446,7 +463,7 @@ The :py:meth:`~PIL.Image.Image.save` method supports the following options:
     If this parameter is not provided, the image will be saved with no profile
     attached. To preserve the existing profile::
 
-        im.save(filename, 'jpeg', icc_profile=im.info.get('icc_profile'))
+        im.save(filename, "jpeg", icc_profile=im.info.get("icc_profile"))
 
 **exif**
     If present, the image will be stored with the provided raw EXIF data.
@@ -910,7 +927,7 @@ Saving
 The extension of SPIDER files may be any 3 alphanumeric characters. Therefore
 the output format must be specified explicitly::
 
-    im.save('newimage.spi', format='SPIDER')
+    im.save("newimage.spi", format="SPIDER")
 
 For more information about the SPIDER image processing package, see
 https://github.com/spider-em/SPIDER

src/PIL/IcoImagePlugin.py

@@ -22,6 +22,7 @@
 #   * https://msdn.microsoft.com/en-us/library/ms997538.aspx
 
 
+import os
 import warnings
 from io import BytesIO
 from math import ceil, log
@@ -347,6 +348,85 @@ class IcoImageFile(ImageFile.ImageFile):
         pass
 
 
+def _ico1_accept(prefix):
+    return prefix[:2] == b"\1\0"
+
+
+class Ico1ImageFile(ImageFile.ImageFile):
+    format = "ICO1"
+    format_description = "Windows 1.0 Icon"
+
+    def _open(self):
+        if not _ico1_accept(self.fp.read(2)):
+            msg = "not an ICO1 file"
+            raise SyntaxError(msg)
+
+        self.fp.seek(4, os.SEEK_CUR)
+        width = i16(self.fp.read(2))
+        height = i16(self.fp.read(2))
+        self._size = (width, height)
+        self._mode = "LA"
+
+        self.tile = [("ico1", (0, 0) + self.size, 14, None)]
+
+
+class Ico1Decoder(ImageFile.PyDecoder):
+    _pulls_fd = True
+
+    def decode(self, buffer):
+        data = bytearray()
+        bitmapLength = self.state.xsize * self.state.ysize // 8
+        firstBitmap = self.fd.read(bitmapLength)
+        secondBitmap = self.fd.read(bitmapLength)
+        for i, byte in enumerate(firstBitmap):
+            secondByte = byte ^ secondBitmap[i]
+            for j in reversed(range(8)):
+                first = byte >> j & 1
+                second = secondByte >> j & 1
+                data += b"\x00" if (first == second) else b"\xff"
+                data += b"\x00" if first else b"\xff"
+        self.set_as_raw(bytes(data))
+        return -1, 0
+
+
+class Ico1Encoder(ImageFile.PyEncoder):
+    _pushes_fd = True
+
+    def encode(self, bufsize):
+        firstBitmap = bytearray()
+        secondBitmap = bytearray()
+        w, h = self.im.size
+        for y in range(h):
+            for x in range(w):
+                l, a = self.im.getpixel((x, y))
+                if x % 8 == 0:
+                    firstBitmap += b"\x00"
+                    secondBitmap += b"\xff"
+                if not a:
+                    firstBitmap[-1] ^= 1 << (7 - x % 8)
+                if not l:
+                    secondBitmap[-1] ^= 1 << (7 - x % 8)
+        data = firstBitmap + secondBitmap
+        return len(data), 0, data
+
+
+def _ico1_save(im, fp, filename):
+    if im.mode != "LA":
+        msg = f"cannot write {im.mode} as ICO1"
+        raise OSError(msg)
+
+    fp.write(
+        o16(1)  # device-independent format
+        + o32(0)  # not used
+        + o16(im.size[0])  # width in pixels
+        + o16(im.size[1])  # height in pixels
+        + o16(im.size[0] // 8)  # width in bytes
+        + o16(0)  # not used
+    )
+
+    ImageFile._save(im, fp, [("ico1", (0, 0) + im.size, 0, None)])
+
+
 #
 # --------------------------------------------------------------------
 
@@ -356,3 +436,9 @@ Image.register_save(IcoImageFile.format, _save)
 Image.register_extension(IcoImageFile.format, ".ico")
 
 Image.register_mime(IcoImageFile.format, "image/x-icon")
+
+Image.register_open(Ico1ImageFile.format, Ico1ImageFile, _ico1_accept)
+Image.register_save(Ico1ImageFile.format, _ico1_save)
+
+Image.register_decoder("ico1", Ico1Decoder)
+Image.register_encoder("ico1", Ico1Encoder)