It's pretty outdated now, but I believe when it was popular several years ago (should have indicated that in my post I was talking about an outdated concept), the theory was the epson driver resizing was weak so forcing it to be an even number would give the best results.
Hi Wayne,
Actually, things look pretty bleak even nowadays. The resampling still seems to be crude (and thus simple to implement and fast and requires little driver or dithering firmware intelligence). This coarse (bilinear?) resampling is only causing part of the loss of quality.
I think the other popular thing back then was to enlarge it was better to do so at 10% increments up to the final size. but the concept came from the idea that somewhere in the pipeline the image would be resized to the machines "internal" dpi of 360 or 720.
The step resampling kind of worked, because the halos and ringing at higher detail level (still larger sizes than final) was kind of offsetting the loss of contrast of the next step down. But much better quality can already be achieve in a single step by using more complex algorithms.
I think most now resize to either 360, either by creating a secondary file or using something like LR. And as you pointed out, that doesn't eliminate aliasing, just sort of create different type of aliasing.
Yes, 360
PPI (which is printed with much higher
DPI dot or droplet placement resolution) is approx. consistent with the acuity of human vision at reading distances in adequate illumination conditions. However, there are benefits to resampling to 720 PPI or, to get back to the original questions, shooting at higher resolutions even if the lens is a relatively modest performer, in order to allow capture and printing at 720 PPI rather than having to upsample.
Attached I've added a couple of sample patterns (TIFFs in 16-b/ch Adobe RGB colorspace). I've also added direct links in case the TIFFs do not attach/display well.
1. A sinusoidal cycle sweep going from effectively a 180 PPI resolution (~=3.54 cy/mm) to a 360 PPI resolution (~=7.09 cy/mm) at the top of the image, sampled at a 360 PPI resolution. This one should be printed at 360 PPI on Epson printers (with the 'Finest detail' option switched
off), and would measure (720 pixels @ 360 per inch =) 2 inches in length.
Direct link to original file 2. The same sinusoidal cycle sweep, but now sampled at 720 PPI resolution. It's as if we used the same lens but with a sensor that has twice the resolution, well, sort of. This one should be printed at 720 PPI on Epson printers (with the 'Finest detail' option switched
on), and would also measure (1440 pixels @ 720 per inch =) 2 inches in length.
Direct link to original fileThe difference in output quality may or may not be clearly visible in print (depending on paper used and how well the head alignment and paper transport is calibrated), but when pixelpeeping the files, e.g. at the top righthand corner, it should be clear that the pattern at the maximum 360 PPI effective 'captured' resolution is much more accurately defined in the 720 PPI file version, and thus much easier to print and sharpen well (even if the printer driver+OS resampling is a bit lacking). So capturing with a higher resolution sensor, even of a modestly performing lens (360 PPI on a 720 PPI capable resolution) is worthwhile.
This oversampled image capture will also allow much better capture sharpening at the higher resolution. We may even benefit from upsampling the lower resolution image, and sharpening that (more accurately because more pixels to do it smoothly for intermediate tones).
Oh, and while we are on this lateral (but related) discussion of print resolution, printing at 720 PPI will of course allow to print twice the resolution, which means we can use half the viewing distance, or print twice as large, without visual loss. This assumes that the lens+sensor are able to capture enough detail. Stitching may be needed t achieve large output, but that's always an option (if the subject matter allows).
Cheers,
Bart
