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Originally Posted by picard_beta
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it took me longer to figure it out and the joy was not about the math skills (it was just a funny statement), but realizing that i can mirror with hw idct.
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Yes, I agree it's a good thing that we can do that so simply.
Every other column (or line) corresponds to a "odd" or "even" cosine function, starting with "even". the "even" one are symetrical in the mirroring, and the "odd" ones get sign-inverted, so it would seem logical that by changing the sign of the coefficient of all the "odd" routines, the result will be mirrored, and you can do it in either direction or in both, in which case you should end-up with the 180 degree rotation of the block, if i am not mistaking.