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funzoom

$ \bigcirc$Name


funzoom Image reduction by projection on a B-spline space




$ \bigcirc$Command Synopsis


funzoom [-z z] [-x tx] [-y ty] [-o o] in out



-z z : unzoom factor (default 2.0)

-x tx : to first translate (x) the original image

-y ty : to first transalte (y) the original image

-o o : spline space order, 0..5, default 0

in : input Fimage

out : output Fimage




$ \bigcirc$Function Summary


Fimage funzoom (in , out , z , o , tx , ty )

Fimage in , out ;

float *z , *tx , *ty ;

int *o ;




$ \bigcirc$Description


This module unzooms an image by a factor z. The input image is first projected orthogonally onto the space of B-splines of order n (see the fcrop module). The order n can be specified by the -o option. Then, an appropriate subsampling is performed. Hence, the L2 norm of the error caused by image reduction is minimized. This method, described in [UAE95], allows to avoid undesirable artifacts like aliasing.


$ \bullet$ If n = 0, the method is a simple averaging under the assumption that pixel are adjacent squares. The input image u is supposed to take constant values in each 1×1 square (nearest neighbor interpolation), and the output value at a given pixel is given by the average of u on the corresponding z×z square. In particular, this yields the classical simple ``block averaging'' for integer reduction factors.


$ \bullet$ For n $ \geq$ 1, the algorithm consists in two steps :

1. a zoom by a certain cubic (non-regular) spline, $ {\frac{1}{z}}$$ \beta^{1}_{z}$*$ \beta^{1}_{}$, where $ \beta^{1}_{}$ is the B-spline of order 1 and $ \beta^{1}_{z}$(x) = $ \beta^{1}_{}$(x/z).

2. an inverse spline transform of order 3, performed by the finvspline module.




$ \bigcirc$See Also


fdirspline, finvspline.

cfunzoom, fzoom.


$ \bigcirc$Version 2.3


Last Modification date : Tue Feb 19 13:45:23 2002


$ \bigcirc$Author


Lionel Moisan






next up previous contents index
Next: fzoom Up: Reference Previous: fsample   Contents   Index
mw 2004-05-05