Add support for ATI1/2(BC4/BC5) DDS files

This commit adds support for loading DDS with ATI1 and ATI2 fourcc pixel format

Tests/test_file_dds.py

@@ -10,6 +10,7 @@ from .helper import assert_image_equal, assert_image_equal_tofile, hopper
 TEST_FILE_DXT1 = "Tests/images/dxt1-rgb-4bbp-noalpha_MipMaps-1.dds"
 TEST_FILE_DXT3 = "Tests/images/dxt3-argb-8bbp-explicitalpha_MipMaps-1.dds"
 TEST_FILE_DXT5 = "Tests/images/dxt5-argb-8bbp-interpolatedalpha_MipMaps-1.dds"
+TEST_FILE_ATI2 = "Tests/images/ati2.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"
@@ -62,6 +63,19 @@ def test_sanity_dxt5():
     assert_image_equal_tofile(im, TEST_FILE_DXT5.replace(".dds", ".png"))
 
 
+def test_sanity_ati2():
+    """Check ATI2 images can be opened"""
+
+    with Image.open(TEST_FILE_ATI2) as im:
+        im.load()
+
+        assert im.format == "DDS"
+        assert im.mode == "RGB"
+        assert im.size == (128, 128)
+
+        assert_image_equal_tofile(im, TEST_FILE_ATI2.replace(".dds", ".png"))
+
+
 @pytest.mark.parametrize(
     ("image_path", "expected_path"),
     (

src/PIL/DdsImagePlugin.py

@@ -82,7 +82,6 @@ DDS_CUBEMAP_NEGATIVEY = DDSCAPS2_CUBEMAP | DDSCAPS2_CUBEMAP_NEGATIVEY
 DDS_CUBEMAP_POSITIVEZ = DDSCAPS2_CUBEMAP | DDSCAPS2_CUBEMAP_POSITIVEZ
 DDS_CUBEMAP_NEGATIVEZ = DDSCAPS2_CUBEMAP | DDSCAPS2_CUBEMAP_NEGATIVEZ
 
-
 # DXT1
 DXT1_FOURCC = 0x31545844
 
@@ -193,6 +192,14 @@ class DdsImageFile(ImageFile.ImageFile):
                     raise NotImplementedError(
                         f"Unimplemented DXGI format {dxgi_format}"
                     )
+            elif fourcc == b"ATI1":
+                self.pixel_format = "BC4"
+                n = 4
+                self.mode = "RGB"
+            elif fourcc == b"ATI2":
+                self.pixel_format = "BC5"
+                n = 5
+                self.mode = "RGB"
             else:
                 raise NotImplementedError(f"Unimplemented pixel format {repr(fourcc)}")