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Topic: sub-pixel shifting of a matrix
Replies: 14   Last Post: Feb 7, 2013 12:23 PM

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Shalin Mehta

Posts: 6
Registered: 9/17/09
Re: sub-pixel shifting of a matrix
Posted: Sep 17, 2009 5:33 AM
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Just found a useful solution: Use interp2 with '*linear' option. Works factor of 2.5 faster than imtransform. Any other ideas?

"Shalin Mehta" <> wrote in message <h8ss9r$jhf$>...
> Hello world,
> I have data defined over a grid, e.g.
> [xx yy]=meshgrid(-1:0.1:1); %each pixel represents distance of 0.1
> data=xx.^2+yy.^2 ;
> I need to translate this data by sub-pixel distances which will inevitably involve interpolation. I can live with linear interpolation as the data is sampled quite finely. I am using imtransform to achieve this. The shifted-data need to be obtained only over the original grid. I want extrapolated locations to be zero.
> xshift=0.235; yshift=-0.95; %Since shift is finer than sampling, sub-pixel shifting is required.
> xdata=[1 wt];
> ydata=[1 ht];
> T=maketform('affine',[1 0 0; 0 1 0; xshift yshift 1]);
> shifteddata=imtransform(data,T,'bilinear','XData',xdata,'YData',ydata);
> Results are satisfactory but slow as this shifting happens in the inner-most loop.
> Can anyone suggest a method that involves direct indexing and hence would be faster? Any neat algorithm published in the literature for sub-pixel translation?
> best
> Shalin

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