from PIL import Image
import sys
p = sys.argv[1]
img = Image.open(p).convert("L")
W, H = img.size
px = img.load()
# edge density per row: count |v(x)-v(x-2)| > 40
rows = []
for y in range(H):
    c = 0
    for x in range(2, W):
        if abs(px[x, y] - px[x-2, y]) > 45:
            c += 1
    rows.append(c)
# report top rows grouped
thr = max(20, sorted(rows)[int(H*0.97)])
print("W,H", W, H, "row-edge threshold", thr)
bands = []
y = 0
while y < H:
    if rows[y] > thr:
        y0 = y
        while y < H and rows[y] > thr:
            y += 1
        bands.append((y0, y, max(rows[y0:y])))
    y += 1
for b in bands[:40]:
    print("band y=%d..%d maxedge=%d" % b)