Run-Length Decoding of almost-random data

[Alexander Rhatushnyak]

The attached small Python script creates an image that looks,
if you turn on your imagination and look from different angles, |_ \_ --.--
like a flower, or maybe a head with a couple eyes and a smiling mouth...
Zoom level should be set to 100% during the looking with imagination exercise

import math,sympy
Size = 1025  # must be an odd number
offset = Size>>1  # so the center is at (512,512) if Size==1025 

def get_x_y(n):  # this function is from http://oeis.org/A235913
  sr = int(math.sqrt(n-1))  # OK for relatively small n's
  sr = sr-1+(sr&1)
  rm = n-sr*sr
  d = (sr+1)/2
  if rm<=sr+1:
     return -d+rm, d
  if rm<=sr*2+2:
     return d, d-(rm-(sr+1))
  if rm<=sr*3+3:
     return d-(rm-(sr*2+2)), -d
  return -d, -d+rm-(sr*3+3)

outfile = open("outfile_42.ppm", "wb")
outfile.write("P6\n"+str(Size)+" "+str(Size)+"\n255\n")
data = [4] * (Size*Size)
p = runLength = 1
print 'Starting the main loop...'
for i in range(Size*Size):            # runs ~2 seconds if Size==1025
        runLength -= 1
        if runLength==0:
            p = sympy.nextprime(p+1)
            colorCode = (p & 7) >> 1   #  extract 3 bits, discard the last bit, it's always a 1
            runLength = (p >> 3) % 42 + 1  #  42 is a magic number
            x,y = get_x_y(i+1)
            data[x+offset+(y+offset)*Size] = colorCode

print 'Writing image file...'
for x in range(Size):        # also ~2 seconds if Size==1025
  for y in range(Size):
    rgb = [0,0,0]
    v = data[x+y*Size]
    if v<4:
      numNeighbors = 0
      for i in range(x-3, x+3 +1):
        for j in range(y-3, y+3 +1):
          if i>=0 and j>=0 and i<Size and j<Size and data[i+j*Size]<4:  numNeighbors+=1
      if numNeighbors > 1:   #  apply some noise reduction.  > 0 to skip noise reduction
        if v<3: rgb[v] = 255
        elif v==3:  rgb[0] = rgb[1] = rgb[2] = 255
    for c in rgb: outfile.write(chr(c))
outfile.close()

[Alexander Rhatushnyak]

Same code but Size=1199 and magic number 110 instead of 42: http://qlic.altervista.org/size1199_mn110.gif
Horizontal lines near the bottom, something with many visible edges near the upper-right corner.

[Alexander Rhatushnyak]

If anyone is interested in reading & commenting
the text & slides of my talk at Starcon a month ago,
please let me know, I'll email them to you.