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Lag N Crash 2025
For some reason, it seems as though this folder of pixels are not what they seem. Can you find out what is going on?
we are provided with a zip file, pixels.zip. unzipping gives a pixels/ directory with 625 subfolders, each named pixel_<row>_<col> (rows and cols going from 0 to 24). every folder holds a single 500x500 png.
opening a few of the pngs, they’re all just solid colour, either fully black or fully white. 625 = 25*25, so the folder name basically tells you where that tile goes in a 25x25 grid. one image = one qr module.
from here it’s just reconstruction. sample the centre pixel of each tile (since each png is uniform), stitch them into a 25x25 grid, scale up so it’s actually scannable, and slap on a quiet zone so pyzbar doesn’t complain.
from PIL import Image
from pyzbar.pyzbar import decode
N = 25
MODULE = 20 # px per module
BORDER = 4 # quiet zone in modules
size = (N + 2 * BORDER) * MODULE
img = Image.new('L', (size, size), 255)
for r in range(N):
for c in range(N):
tile = Image.open(f'pixels/pixel_{r}_{c}/pixel_{r}_{c}.png').convert('L')
v = tile.getpixel((250, 250))
colour = 0 if v < 128 else 255
for dy in range(MODULE):
for dx in range(MODULE):
x = (c + BORDER) * MODULE + dx
y = (r + BORDER) * MODULE + dy
img.putpixel((x, y), colour)
img.save('qr.png')
print(decode(img))run it, scan the qr, get the flag!
