67 lines
1.8 KiB
Markdown
67 lines
1.8 KiB
Markdown
# Quick Response - misc
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fridgebuyer
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- The QR is 29x29 == version 3
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- Each module = 32x32 px
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- What should be solid is alternated. The 7x7 finder patterns should be solid but are not visible in the 3 corners (top left, bottom left, top right)
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- What should be alternated are solid lines (timing strips)
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- So the original QR was likely XORed with a Checkerboard pattern
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- https://www.pclviewer.com/rs2/qrmasking.htm Mask 000: (i + j) mod 2 = 0 is this
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- But this was applied to entire qr code, not only to the data region
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- So need to XOR every module with (row + col) % 2 again.
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### sol
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```
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from PIL import Image
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import numpy as np
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from pyzbar.pyzbar import decode
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img = Image.open("quick-response.png").convert("RGB")
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arr = np.array(img)
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# extract module grid
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module_size = 32
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n = 29
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dark = np.array([20, 22, 27])
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grid = np.zeros((n, n), dtype=int)
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for r in range(n):
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for c in range(n):
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cy = r * module_size + module_size // 2
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cx = c * module_size + module_size // 2
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pixel = arr[cy, cx]
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if np.sum((pixel.astype(int) - dark.astype(int)) ** 2) < 100:
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grid[r, c] = 1
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# XOR (i + j) mod 2 = 0
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for r in range(n):
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for c in range(n):
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grid[r, c] ^= (r + c) % 2
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# write fixed QR code
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scale = 10
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border = 4
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total = (n + 2 * border) * scale
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out = Image.new("L", (total, total), 255)
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px = out.load()
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for r in range(n):
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for c in range(n):
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if grid[r, c] == 1:
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for dy in range(scale):
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for dx in range(scale):
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px[(c + border) * scale + dx, (r + border) * scale + dy] = 0
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result = decode(out)
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for r in result:
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print(r.data.decode())
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```
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**gigem{d1d_y0u_n0t1c3_th3_t1m1n9_b175}**
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