[Numpy-discussion] nd_image.affine_transform edge effects
Stefan van der Walt
stefan at sun.ac.za
Thu Apr 5 06:15:30 EDT 2007
Hi James
On Wed, Apr 04, 2007 at 08:29:50PM -0400, James Turner wrote:
> > It looks like the last output value is produced by reflecting the
> > input and then interpolating, but presumably then the first value
> > should be 3.9, for consistency, not 3.1? Does that make sense?
>
> Aargh. I think I see what's happening now. The input is supposed to
> be interpolated and then reflected like this:
>
> [4 3 2 1] -> [3.1 3.1 2.1 1.1 1.1]
>
> The problem is that there is still one value too many being
> "interpolated" here before the reflection takes place. Do the
> sections beginning at lines 168 & 178 need changing in a similar way
> to their counterparts at lines 129 & 139? I started looking into
> this, but I don't understand the code well enough to be sure I'm
> making the right changes...
Thanks for spotting that. When I fix those lines, I see:
[[ 3.9000001 3.0999999 2.0999999 1.10000002 1.89999998 2.9000001 ]
[ 3.9000001 3.0999999 2.0999999 1.10000002 1.89999998 2.9000001 ]]
I'll submit to SVN later today. Note that I also enabled 'mirror'
mode, which works almost the same way as reflect:
Reflect: 1 2 3 4 -> 1 2 3 4 4 3 2 1
Mirror: 1 2 3 4 -> 1 2 3 4 3 2 1
Cheers
Stéfan
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