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fix small error in brachiosaure wu 

Signed-off-by: Julien CLEMENT <julien.clement@epita.fr>
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Julien CLEMENT 2023-05-01 17:22:19 +02:00
parent e11eceaa85
commit f3e0ce09f6
1 changed files with 5 additions and 4 deletions
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jujure/content/writeups/fcsc_2023/brachiosaure.md
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@ -298,9 +298,10 @@ And there is a really interesting property indeed:
{{< image src="/brachiosaure/invertible.png" style="border-radius: 8px;" >}}
By adding empty matrices and an identity matrix in the bottom right corner, the
resulting matrix is always invertible, and the inverse can be trivially computed
since it is simply moving matrices arround and negating the original image modulo 256 `notice the "-(QRuser)" in the inverted matrix`.
By adding identity matrices and an empty matrix in the bottom right corner, the
resulting matrix is always invertible, and the inverse can be trivially
computed since it is simply moving matrices arround and negating the original
image modulo 256 `notice the "-(QRuser)" in the inverted matrix`.
## Putting everything together
@ -370,4 +371,4 @@ inverse matrix:
- We add identity matrices: they only have the diagonal set to 1 so only a little bit grayer than the black, no noise visible by naked eyes
- We add the opposite of the matrix, and this is the clean part: our original matrices only hold black and white pixels so respectively `0x0` and `0xff`, so the opposite of `0` is still `0` and the opposite of `0xff` if `1` modulo 256, so like the identity matrix, they are nearly invisible. If you look closely though :eyes: you will see that all white pixels of the QR code were indeed reflected as very faint taint of gray in its inverse matrix on the other image.
- We add the opposite of the matrix, and this is the clean part: our original matrices only hold black and white pixels so respectively `0x0` and `0xff`, so the opposite of `0` is still `0` and the opposite of `0xff` if `1` modulo 256, so like the identity matrix, they are nearly invisible. If you look closely though :eyes: you will see that all white pixels of the QR code were indeed reflected as very faint taint of gray in its inverse matrix on the other image.