Hi Samuel,
That's correct. Panorama stitching is often very much like distortion correction, some areas can get enlarged, others can get reduced in size, in the same image.
LR uses a decent downsampling method (better than Bicubic and certainly better than Bicubic Sharper), although I do not know what it is exactly. The upsampling has some resemblance to bilinear. However, there may also be adaptive (to the image content) features at play. But the difficulty with stitching is the small rotations and enlargements/reductions. That will lose detail pretty quickly if the wrong method is used. Since LR's stitching is Raw input based, it's not easy to simulate with synthetic images which would show the trade-offs more quickly.
Dedicated stitchers like PTGUI could produce multiple conversions with the same pixel dimensions but interpolated/scaled with different filters, and the user can then blend the best parts manually, e.g. Lanczos2 for high contrast edges with sharp edge detail (yet with minimal halo), and a higher support version of Lanczos for structural detail, where ringing artifacts will be harder to see (if at all) due to the variable detail.
Cheers,
Bart
Hi Bart,
That's a nice way of looking at panorama stitching :-)
Yes, I recall reading your posts on downsampling interpolation in LR. How interesting that it is neither Bicubic nor Bicubic sharper. If I am not mistaken, in Photoshop, when Bicubic (automatic) is chosen, upsampling should use Bicubic Smoother. Strange that it resambles bilinear in LR!
I wonder if photographs of highly detailed targets could be captured, and then put through the paces of LR's stitching and PTGui, to reveal the trade-offs.
For my landscape pano stitches I am usually using Lanczos 8 in PTGui, with excellent results.
Interpolation to me is very important, I'm sad that it is not more vigorously discussed. I never saw it mentioned once in two recent lu-la articles on focus stacking. The whole point of that is to increase in-focus detail, so using an interpolator that makes everything softer is counter to the purpose. Unfortunately for the majority of the LR audience, a simple turn-key solution is preferable over fussing about such issues.
P.S. I had the opportunity to study at close range some billboard prints from Apple's 'Shot on iPhone 6' campaign, and they look surprisingly good. I wonder what upsampling software they used for those.