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## Re: where is area?

 From: Luiz Portella Subject: Re: where is area? Date: Thu, 8 Sep 2011 20:43:32 -0300

```James,

Well, I think for 90 and 180 Octave dont work with interpolation, it
changes numbers from cell-x to cell-y, that's all.
For 0 degree I think Octave dont touch the matrix. Sum of all cells
for this is 4. That's right.

For 45 and 135 I hope get something about 4, like 3,96 or 3,94. But I
get 3,52944 for both...
Wikipedia put formulas with aprox., and 3,52944 are not aprox. 4.

Thanks! Luiz

>> For 0, 90 and 180 the sum of this numbers are 4, but not for 45 and
>> 1350! What? I dont understand.... All for cell with 1 (there are 4) is
>> inside matrix 5x5, away from border.
>> Thanks a lot.
>
> I'm not sure why you would expect them to be equal.  Bilinear interpolation
> is not linear.
> http://en.wikipedia.org/wiki/Bilinear_interpolation
> It "works" in your case for 0, 90, and 180 because these are degenerate
> cases were the rotated image points lie on the original grid so the points
> are linear interpolations of two pixels and not a function of all 4
> neighboring pixels.

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