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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
2011/9/8 James Sherman Jr. <address@hidden>:
>*> 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.*
--
Luiz Portella address@hidden