Bart:
Trying to sort things out at the perceptual level, it appears to me that EWA RobidouxSharp through linear RGB is generally both sharper and (this is the important bit) has less noticeable haloing than LWGBautolevelGamma3s100. And yet it introduces less moire.
EWA Mitchell through linear RGB, for example, looks really good in the sharpness/halo ratio department. Nice balanced scheme.
Am I missing something? (Away from my large calibrated monitor, but I don't think it matters.)
Hi Nicolas,
After my initial investment in time, I tried to avoid changing too many things too fast. I preferred waiting for some user feedback, likes, dislikes, the dust to settle as it were. It's just a case of not trying to aim at a moving target until it slows down enough, to take a shot, and then aim at the next target.
As I said
in an earlier post, I'd like to test more Keys Cubic settings if time allows. However, until the deconvolution (if any) is automated, it takes a lot of time to do right. I therefore wanted to optimize the setting that
you found to be useful (for 'minimizing the worst case deviation from the original value'), before benchmarking against (less robust?) alternatives, and also use the insights that were gained in the course of experimentation and code-optimization.
P.S. OK. Maybe LWGBautolevelGamma3s100 is a nudge sharper. It's less sharp than EWA CatRom through linear light, though, and CatRom does not seem to add an amount of haloing that matches the additional sharpness.
What I don't see is obvious advantages of the new downsampling methods over simply pushing the Keys alpha up from 0 until the sharpness is sufficient.
Again: Am I missing something? (I hope I am.)
We'll have to see how well they perform when scrutinized for aliasing(!)/ringing/blocking behavior (which may also affect rendering of down-sampled noise), and the risk of clipping due to halo under- / over-shoots. I would think that a user controllable Keys alpha input (on a scale from soft to sharp/crisp, or 0% to 100%) to adjust the behavior of the resampling filter should be a parameter for a modern resizing tool. Of course, the negative side effects (from softness to artifacts) should also be minimized in the background.
(I reserve my opinion w.r.t. upsampling. Different game.)
Absolutely, different game, different rules.
Cheers,
Bart
P.S. Different values for Keys alpha will not only require different deconvolution filter values, but also different gammas than 3.0 for a balanced halo under- / over-shoot. High alpha values will require significantly higher gammas, which may be risky in a non-floating point processing environment, but more experimentation will be required to make sure.