49 Shades of Gray

Challenge
We only have 49 shades of gray

000000 to F5F5F5… there’s one shade missing! Find the hex value of the missing shade. Pound sign optional.

Image

Solution

They tell us there are 50 shades of gray, ranging from 0 to 245 (0xF5). This would mean there is a shade of gray made from every pixel value divisible by 5 between those two values (#000000 #0a0a0a #0f0f0f etc) ..except one. We find out which one with a small

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from PIL import Image

img=Image.open("shades.png")

pixels=img.load()
(width,height)=img.size

for i in xrange (0,250,5):
  found = 0
  for w in range (0,width):
    for h in range (0,height):
       if pixels[w,h][0] == i:
         found=1
         break
  if not found:
      print "shade not found: "+str(i)

when we run this we find

` shade not found: 80 `

which in hex is 50, so the missing shade of gray is #505050, which we submit as our flag

Flag