Proxel Lens Corrector

Started Aug 28, 2006 | Discussions thread
Roland Karlsson Forum Pro • Posts: 27,539
Re: PTLens update

KL Matt wrote:

If I understand correctly, Proxel stretches the corners instead of
shrinking the middle for barrel distortion, right? So
theoretically, the very center of the image will have almost
exactly the same resolution and sharpness as the original before
any correction. The corners will also have the same resolution, but
a percentage of those pixels will have been interpolated. With
PTlens, it appears the center is shrunk, forcing more original
pixels into the space of fewer "converted" pixels in the middle and
leaving the edges relatively unmolested exept for the fact that the
resolution of the entire image is lessened due to the subsequent
cropping that is necessary.

So for barrel distortion, Proxel does indeed sound like it would
preserve center resolution and sharpness, at the expense of edge
sharpness (but not resolution). But what about pincushion
distortion? Won't Proxel expand the middle of the image to fill up
the top and bottom, interpolating most heavily right in the middle
of the image? Can this degrade center sharpness? Or does Proxel
swich to the other (i.e. shrink-the-corners) method for pincushion
(I assume this would be better for center sharpness, although
leading to overall lower resolution)?

Sounds like a correct analysis.

By default - the Proxel Lens Corrector preserves the center sharpness both for barrel and pin cushion distortion, i.e. the center scaling is 1.0. We believe that, for all pictures with normal degree of distortion, it is best to not do any interpolation in the middle of the picture - neither up nor down scale. Then you will preserve the quality of the picture in the middle - where it is most important and where lenses are optimally sharp.

If you, e.g. for pin cushion, want to upscale the middle, then you can set the scale factor to something larger than 1.0, e.g. 1.5, and the program will automaticaly determine the canvas size for that scale factor.

To me, the PTLens method, although lowering resolution, sounds like
it should provide overall sharper results. Apparently this is not
your experience? I always thought up-resing was worse for sharpness
than down-resing.

Up-resizing makes the picture (at pixel level) more blurry, but down-resizing loses information. Down-resizing will give you a sharper per pixel picture, but up-resizing wil preseve the overall sharpness.

I think I need to do some experiments of my own!

Good luck with your experiments!

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