Lancos is a resampling filter and as such needs a resampling area (that is a Elliptical Weighted Average).
Without EWA you can't use Lancos, but you can use a 'scale-less' single point lookup... That is Interpolation!
The EWA may actually work, as the function derivative, which is what is needed for determining the sampling Ellipse, is actually easily determined for a polynomial. An easy way to check would be to use to shrink the output image (easy why to do this is use -define distort:scale=0.2
to shrink the output viewport). If you get good anti-aliasing then EWA is working, otherwise you get single point interpolation, and severe aliasing.
An alternative is to set -interpolate background
(interpolate always returns background color). If you then only get the background color in the resulting image, EWA is disabled! You can verify that this happens by specifically disabling resampling (and thus EWA) using -filter point
to force IM to fall back to using interpolation.
Using all the above methods, I have confirmed EWA is being used.
There are lots of ways to skin a cat, and what method you use depends
on what you want that skin for, and how messy you like the results!
-- Anthony Thyssen
Added to "Polynomial Distort" http://www.imagemagick.org/Usage/distorts/#polynomial
Due Polynomial Distortion being non-reversible, it isn't posible for IM to calculate the 'best-fit' of the destination image's viewport, for a given source image. As such the "+distort" form of the operator does not work, and falls back to a normal "-distort" operation. You can however still use the Distort Viewport option to define the viewport of the destination image.
With appropriate links of course.
I have confirmed this using -verbose
IF a viewport image was created due to +distort
option would show output appropriate -size
commands to generate a viewport of a destination image, that is different to the input image. Setting a -define distort:viewport
does generate those commands in the verbose output.