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by frud
998 days ago
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His method for computing entropy is not so good. His method works for an independent and unpredictable sequence of bytes, but the actual data is a bunch of signed 16-bit residuals that presumably are normally distributed. Really, he should be measuring the entropy of the original heightmap, but instead he is measuring the entropy of the heightmap after he has applied a couple of confounding transformations (predictive filter, words->byte pairs, and a random shuffle) that act to increase the apparent entropy. Calculating the exact entropy of data is at least as difficult as breaking encryption. Encrypted data should be indistinguishable from random (full-entropy) noise, but really its entropy should be the entropy of the plaintext data plus the entropy of the encryption key. |
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