Dec 13: Ball in plain sight!?!

Challenge

… here it is, but will you be able to reveal it’s secret?

BALL-O-MATIC

There are days, in which you don’t get immediately the HV15-Nugget. This is such a day! Put the resulting flag or sentence of the day here and get the only counting HV15-Nugget

Solution

So we are looking for a hidden message, but it will not be the HV15- string.

Playing around with various settings in GIMP we can see that there are some letters hidden in the images, but we can’t quite make out what it says:

We check out the pixel values in python and notice that most values are odd..

Hmm, lets see what we get when we only output the pixels with even pixel value in the red channel:

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from PIL import Image

img = Image.open('ball_3h6SOemwRR_PmQhXh2AM.png')
pixels_orig = img.load()
(w,h)=img.size

outimg = Image.new( 'RGB', (w,h), "white")
pixels_out = outimg.load()

for i in range(0,h):
    for j in range(0,w):
      (r,g,b) = pixels_orig[j,i]
      if(r%2==0):
          pixels_out[j,i]=(0,0,0)

outimg.save("dec13_evenredval.png","png")

We get the following image:

Aha! seems like we’re on the right track :) ..Let’s check out the other channels. The green channel gives nothing, but blue yields:

XKCD comic 26 is:

Ok, let’s try taking the fourier transform with imagemagick:

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$ convert ball_3h6SOemwRR_PmQhXh2AM.png -fft  +depth +adjoin fourier-%d.png

this gives two images, the magnitude and the phase:

The magnitude image may appear black, but contains more information than meets the eye. We enhance the image with a log transform to produce a frequence spectrum image:

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$ convert fourier-0.png -auto-level -evaluate log 12000 spectrum.png

We see text in the spectrum! ..this must be what we put in the ball-o-matic to get our nugget.

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f0uRier-ru1ez

Indeed it was, our ball-o-matic turns into our bauble with QR code:

Flag