Have palfix.py always output grayscale

Fixes #431

tools/palfix.py

@@ -4,10 +4,9 @@
 """
 Usage: python palfix.py image.png
 
-Fix the palette format of the input image. Colored images (Gen 2 Pokémon or
-trainer sprites) will become indexed, with a palette sorted {white, light
-color, dark color, black}. Grayscale images (all Gen 1 images) will become
-two-bit grayscale.
+Fix the palette format of the input image to two-bit grayscale.
+Colored images will have their palette sorted {white, light
+color, dark color, black}.
 """
 
 import sys
@@ -18,10 +17,6 @@ def rgb8_to_rgb5(c):
 	r, g, b = c
 	return (r // 8, g // 8, b // 8)
 
-def rgb5_to_rgb8(c):
-	r, g, b = c
-	return (r * 8 + r // 4, g * 8 + g // 4, b * 8 + b // 4)
-
 def invert(c):
 	r, g, b = c
 	return (31 - r, 31 - g, 31 - b)
@@ -33,10 +28,6 @@ def luminance(c):
 def rgb5_pixels(row):
 	yield from (rgb8_to_rgb5(row[x:x+3]) for x in range(0, len(row), 4))
 
-def is_grayscale(palette):
-	return (palette == ((31, 31, 31), (21, 21, 21), (10, 10, 10), (0, 0, 0)) or
-		palette == ((31, 31, 31), (20, 20, 20), (10, 10, 10), (0, 0, 0)))
-
 def fix_pal(filename):
 	with open(filename, 'rb') as file:
 		width, height, rows = png.Reader(file).asRGBA8()[:3]
@@ -52,13 +43,8 @@ def fix_pal(filename):
 		return False
 	palette = tuple(sorted(colors | b_and_w, key=luminance, reverse=True))
 	assert len(palette) == 4
-	rows = [list(map(palette.index, rgb5_pixels(row))) for row in rows]
-	if is_grayscale(palette):
-		rows = [[3 - c for c in row] for row in rows]
-		writer = png.Writer(width, height, greyscale=True, bitdepth=2, compression=9)
-	else:
-		palette = tuple(map(rgb5_to_rgb8, palette))
-		writer = png.Writer(width, height, palette=palette, bitdepth=8, compression=9)
+	rows = [[3 - palette.index(c) for c in rgb5_pixels(row)] for row in rows]
+	writer = png.Writer(width, height, greyscale=True, bitdepth=2, compression=9)
 	with open(filename, 'wb') as file:
 		writer.write(file, rows)
 	return True