mandelbrot-ppm

#!/usr/bin/env python3

from math import log2, log1p
import time

w, h = 900, 720
t1 = time.time()
xc, yc = -0.6, 0.005
mag = 0.65
imax, zmax = 190, 50

blues  = [(v**4, v**2.5, v) for v in (0.2 + x/200 for x in range(160))]
sepias = [(v, v**1.5, v**3) for v in (x/96 for x in range(95, -1, -1))]
rgbcolors = [[int(256 * v) for v in x] for x in blues + sepias]

databytes = bytearray([])
for y in range(h):
    for x in range(w):
        c = complex(xc + (2*x - w) / (w*mag), -yc - (2*y - h) / (w*mag))
        z = complex(0.0, 0.0)
        backgnd = 0
        for i in range(imax):
            z = z * z + c
            if abs(z) >= zmax:
                backgnd = log1p(i + 0.1 - log2(log2(abs(z) + 1))) / 5.25
                break
        databytes += bytearray(rgbcolors[int(backgnd * 255)])

with open('mand.ppm','wb') as fout:
    fout.write("P6\n{} {}\n255\n".format(w,h).encode("ascii"))
    fout.write(databytes)

print("Elapsed time: {:7.2f} s".format(time.time() - t1))