Added support for uncompressed L images

Tests/test_file_dds.py

@@ -22,6 +22,7 @@ TEST_FILE_DX10_BC7 = "Tests/images/bc7-argb-8bpp_MipMaps-1.dds"
 TEST_FILE_DX10_BC7_UNORM_SRGB = "Tests/images/DXGI_FORMAT_BC7_UNORM_SRGB.dds"
 TEST_FILE_DX10_R8G8B8A8 = "Tests/images/argb-32bpp_MipMaps-1.dds"
 TEST_FILE_DX10_R8G8B8A8_UNORM_SRGB = "Tests/images/DXGI_FORMAT_R8G8B8A8_UNORM_SRGB.dds"
+TEST_FILE_UNCOMPRESSED_L = "Tests/images/uncompressed_l.dds"
 TEST_FILE_UNCOMPRESSED_RGB = "Tests/images/hopper.dds"
 TEST_FILE_UNCOMPRESSED_RGB_WITH_ALPHA = "Tests/images/uncompressed_rgb.dds"
 
@@ -194,8 +195,14 @@ def test_unimplemented_dxgi_format():
             pass
 
 
-def test_uncompressed_rgb():
-    """Check uncompressed RGB images can be opened"""
+def test_uncompressed():
+    """Check uncompressed images can be opened"""
+    with Image.open(TEST_FILE_UNCOMPRESSED_L) as im:
+        assert im.format == "DDS"
+        assert im.mode == "L"
+        assert im.size == (128, 128)
+
+        assert_image_equal_tofile(im, "Tests/images/uncompressed_l.png")
 
     # convert -format dds -define dds:compression=none hopper.jpg hopper.dds
     with Image.open(TEST_FILE_UNCOMPRESSED_RGB) as im:
@@ -305,6 +312,7 @@ def test_save_unsupported_mode(tmp_path):
 @pytest.mark.parametrize(
     ("mode", "test_file"),
     [
+        ("L", "Tests/images/linear_gradient.png"),
         ("RGB", "Tests/images/hopper.png"),
         ("RGBA", "Tests/images/pil123rgba.png"),
     ],

src/PIL/DdsImagePlugin.py

@@ -135,7 +135,12 @@ class DdsImageFile(ImageFile.ImageFile):
         fourcc = header.read(4)
         (bitcount,) = struct.unpack("<I", header.read(4))
         masks = struct.unpack("<4I", header.read(16))
-        if pfflags & DDPF_RGB:
+        if pfflags & DDPF_LUMINANCE:
+            # Texture contains uncompressed L data
+            self.mode = "L"
+
+            self.tile = [("raw", (0, 0) + self.size, 0, ("L", 0, 1))]
+        elif pfflags & DDPF_RGB:
             # Texture contains uncompressed RGB data
             masks = {mask: ["R", "G", "B", "A"][i] for i, mask in enumerate(masks)}
             rawmode = ""
@@ -223,9 +228,24 @@ class DdsImageFile(ImageFile.ImageFile):
 
 
 def _save(im, fp, filename):
-    if im.mode not in ("RGB", "RGBA"):
+    if im.mode not in ("RGB", "RGBA", "L"):
         raise OSError(f"cannot write mode {im.mode} as DDS")
 
+    if im.mode == "L":
+        masks = [0xFF000000]
+        pixel_flags = DDPF_LUMINANCE
+    else:
+        masks = [0xFF0000, 0xFF00, 0xFF]
+        if im.mode == "RGBA":
+            pixel_flags = DDS_RGBA
+            masks.append(0xFF000000)
+        else:
+            pixel_flags = DDPF_RGB
+
+    bitcount = len(masks) * 8
+    while len(masks) < 4:
+        masks.append(0)
+
     fp.write(
         o32(DDS_MAGIC)
         + o32(124)  # header size
@@ -234,18 +254,15 @@ def _save(im, fp, filename):
         )  # flags
         + o32(im.height)
         + o32(im.width)
-        + o32((im.width * (32 if im.mode == "RGBA" else 24) + 7) // 8)  # pitch
+        + o32((im.width * bitcount + 7) // 8)  # pitch
         + o32(0)  # depth
         + o32(0)  # mipmaps
         + o32(0) * 11  # reserved
         + o32(32)  # pfsize
-        + o32(DDS_RGBA if im.mode == "RGBA" else DDPF_RGB)  # pfflags
+        + o32(pixel_flags)  # pfflags
         + o32(0)  # fourcc
-        + o32(32 if im.mode == "RGBA" else 24)  # bitcount
-        + o32(0xFF0000)  # rbitmask
-        + o32(0xFF00)  # gbitmask
-        + o32(0xFF)  # bbitmask
-        + o32(0xFF000000 if im.mode == "RGBA" else 0)  # abitmask
+        + o32(bitcount)  # bitcount
+        + b"".join(o32(mask) for mask in masks)  # rgbabitmask
         + o32(DDSCAPS_TEXTURE)  # dwCaps
         + o32(0)  # dwCaps2
         + o32(0)  # dwCaps3