Added support for reading DX10 BC4 DDS images

Tests/test_file_dds.py

@@ -12,6 +12,8 @@
 TEST_FILE_DXT5 = "Tests/images/dxt5-argb-8bbp-interpolatedalpha_MipMaps-1.dds"
 TEST_FILE_ATI1 = "Tests/images/ati1.dds"
 TEST_FILE_ATI2 = "Tests/images/ati2.dds"
+TEST_FILE_DX10_BC4_TYPELESS = "Tests/images/bc4_typeless.dds"
+TEST_FILE_DX10_BC4_UNORM = "Tests/images/bc4_unorm.dds"
 TEST_FILE_DX10_BC5_TYPELESS = "Tests/images/bc5_typeless.dds"
 TEST_FILE_DX10_BC5_UNORM = "Tests/images/bc5_unorm.dds"
 TEST_FILE_DX10_BC5_SNORM = "Tests/images/bc5_snorm.dds"
@@ -82,6 +84,27 @@ def test_sanity_ati1():
         assert_image_equal_tofile(im, TEST_FILE_ATI1.replace(".dds", ".png"))
 
 
+@pytest.mark.parametrize(
+    "image_path",
+    (
+        TEST_FILE_DX10_BC4_UNORM,
+        # hexeditted to be typeless
+        TEST_FILE_DX10_BC4_TYPELESS,
+    ),
+)
+def test_dx10_bc4(image_path):
+    """Check DX10 BC4 images can be opened"""
+
+    with Image.open(image_path) as im:
+        im.load()
+
+        assert im.format == "DDS"
+        assert im.mode == "L"
+        assert im.size == (64, 64)
+
+        assert_image_equal_tofile(im, TEST_FILE_DX10_BC4_UNORM.replace(".dds", ".png"))
+
+
 @pytest.mark.parametrize(
     "image_path",
     (

src/PIL/DdsImagePlugin.py

@@ -98,6 +98,8 @@
 DXGI_FORMAT_R8G8B8A8_TYPELESS = 27
 DXGI_FORMAT_R8G8B8A8_UNORM = 28
 DXGI_FORMAT_R8G8B8A8_UNORM_SRGB = 29
+DXGI_FORMAT_BC4_TYPELESS = 79
+DXGI_FORMAT_BC4_UNORM = 80
 DXGI_FORMAT_BC5_TYPELESS = 82
 DXGI_FORMAT_BC5_UNORM = 83
 DXGI_FORMAT_BC5_SNORM = 84
@@ -190,7 +192,11 @@
                 # ignoring flags which pertain to volume textures and cubemaps
                 (dxgi_format,) = struct.unpack("<I", self.fp.read(4))
                 self.fp.read(16)
-                if dxgi_format in (DXGI_FORMAT_BC5_TYPELESS, DXGI_FORMAT_BC5_UNORM):
+                if dxgi_format in (DXGI_FORMAT_BC4_TYPELESS, DXGI_FORMAT_BC4_UNORM):
+                    self.pixel_format = "BC4"
+                    n = 4
+                    self._mode = "L"
+                elif dxgi_format in (DXGI_FORMAT_BC5_TYPELESS, DXGI_FORMAT_BC5_UNORM):
                     self.pixel_format = "BC5"
                     n = 5
                     self._mode = "RGB"