add BC4 images

nb: the bc4/ati1 dds files are actually slightly wrong, seems like nvtt has a bug and endpoints are off by 1 sometimes

__init__.py

@@ -1,5 +1,6 @@
 from PIL import Image
 from quicktex.s3tc.bc1 import BC1Block
+from quicktex.s3tc.bc4 import BC4Block
 from quicktex import RawTexture
 import os.path
 
@@ -9,7 +10,7 @@ image_path = os.path.dirname(os.path.realpath(__file__))
 class BC1Blocks:
     class Entry:
         def __init__(self, filename, block):
-            path = os.path.join(image_path, 'blocks', filename)
+            path = os.path.join(image_path, 'bc1', filename)
             self.image = Image.open(path).convert('RGBA')
             self.texture = RawTexture.frombytes(self.image.tobytes('raw', 'RGBA'), *self.image.size)
             self.block = block
@@ -17,3 +18,16 @@ class BC1Blocks:
     greyscale = Entry('greyscale_unpacked.png', BC1Block.frombytes(b'\xFF\xFF\x49\x4A\x78\x78\x78\x78'))
     three_color = Entry('3color_unpacked.png', BC1Block.frombytes(b'\xE0\x07\x00\xF8\x29\x29\x29\x29'))
     three_color_black = Entry('3color_black_unpacked.png', BC1Block.frombytes(b'\xE0\x07\x00\xF8\x27\x27\x27\x27'))
+
+
+class BC4Blocks:
+    class Entry:
+        def __init__(self, filename, block):
+            path = os.path.join(image_path, 'bc4', filename)
+            self.image = Image.open(path).convert('RGBA')
+            self.texture = RawTexture.frombytes(self.image.tobytes('raw', 'RGBA'), *self.image.size)
+            self.block = block
+
+    six_value = Entry('6value.png', BC4Block(8, 248, [[0, 1, 2, 3]] * 2 + [[4, 5, 6, 7]] * 2))
+    eight_value = Entry('8value.png', BC4Block(240, 16, [[0, 1, 2, 3]] * 2 + [[4, 5, 6, 7]] * 2))
+