Initial experiments with dithering

dither.py

@@ -0,0 +1,79 @@
+# coding: utf-8
+from PIL import Image
+img = Image.open('peacock.jpg')
+resized = img.resize((128,128))
+hex_colors = """#000000
+#1D2B53
+#7E2553
+#008751
+#AB5236
+#5F574F
+#C2C3C7
+#FFF1E8
+#FF004D
+#FFA300
+#FFEC27
+#00E436
+#29ADFF
+#83769C
+#FF77A8
+#FFCCAA
+#291814
+#111D35
+#422136
+#125359
+#742F29
+#49333B
+#A28879
+#F3EF7D
+#BE1250
+#FF6C24
+#A8E72E
+#00B543
+#065AB5
+#754665
+#FF6E59
+#FF9D81"""
+pico_palette_32 = [x.strip() for x in hex_colors.splitlines()]
+def hex_to_rgb(h):
+    dec = lambda x: int(x, base=16)
+    return (dec(h[1:3]), dec(h[3:5]), dec(h[5:7]))
+
+pico_rgb = [hex_to_rgb(x) for x  in pico_palette_32]
+import numpy as np
+bayer = np.array([[0]])
+np.block([[4*bayer, 4*bayer+3],[4*bayer+2, 4*bayer+1]])
+bayer = np.block([[4*bayer, 4*bayer+3],[4*bayer+2, 4*bayer+1]])
+bayer = np.block([[4*bayer, 4*bayer+3],[4*bayer+2, 4*bayer+1]])
+bayer = np.block([[4*bayer, 4*bayer+3],[4*bayer+2, 4*bayer+1]])
+def dither_pixel(img, xy, pal):
+    global bayer
+    pal2 = [np.array(list(c)) for c in pal]
+    counts = [0]*len(pal)
+    x, y = xy
+    def diff(c1, c2):
+        return sum((c1-c2)**2)
+    def nearest(rgb):
+        cost, index = min((diff(rgb,c), i) for i,c in enumerate(pal2))
+        return index
+    color = np.array(list(img.getpixel(xy)))
+    err = np.array([0,0,0])
+    for _ in range(64):
+        err += color
+        i = nearest(err)
+        counts[i] += 1
+        err -= pal2[i]
+    thresh = bayer[y % 8][x % 8]
+    for i, count in enumerate(counts):
+        thresh -= count
+        if thresh < 0:
+            return i
+
+dithered = Image.new('P', resized.size)
+dithered.putpalette([x for rgb in pico_rgb[:16] for x in rgb])
+import qtdm
+import tqdm
+for x in tqdm.tqdm(range(128)):
+    for y in range(128):
+        i = dither_pixel(resized, (x,y), pico_rgb[:16])
+        dithered.putpixel((x,y), i)