Incredibly slow SRT operation when scaling to small size

[fmw42]

We often suffer from brevity; I should have said it resembles the infinite horizon issue.

No problem. Perhaps I took your comment too literally and more importantly did not read his original post carefully enough. So, I became confused and totally missed the real issue and you had it pinned exactly.

[anthony]

When you get a slow distortion on an image involving extreme reducitons. my first suggestion would to turn off EWA filtering.

That is add -filter point

This means only ONE (unscaled) interpolative lookup is used for each output pixel (at most a 16 pixel lookup limit, depending on the current interpolation setting). It will not attempt to merge (according to the current filter) a large elliptical area of pixels for each output pixel.

If this works you can try using a super-sampling method. That should work especially well for SRT distortions whcih are uniformly scaled across the whole image.