[phkahler]

Backing up to your earlier comment. Pixels on some displays are in fact little squares of uniform color. The question then is how to color a pixel given geometry with detail within that square.

All of this "filtering" is variations on adding blur. In fact the article extends the technique to deliberately blur images on a larger scale. When we integrate a function (which could be a color gradient over a fully filled polygon) and then paint the little square with a solid "average" color that's also a form of blurring (more like distorting in this case) the detail.

It is notable that the examples given are moving, which means moire patterns and other artifacts will have frame-to-frame effects that may be annoying visually. Simply blurring the image takes care of that at the expense of eliminating what looks like detail but may not actually be meaningful. Some of the less blurry images seem to have radial lines that bend and go back out in another location for example, so I'd call that false detail. It may actually be better to blur such detail instead of leaving it look sharper with false contours.

[dahart]

Yes it’s a good point that LCD pixels are more square than the CRTs that were ubiquitous when Alvy Ray wrote his paper. I think I even made that point before on HN somewhere. I did mention in response to Raph that yes the ideal target depends on what the display is, and the filter choice does depend on whether it’s LCD, CRT, film, print, or something else. That said, LCD pixels are not perfect little squares, and they’re almost never uniform color. The ideal filter for LCDs might be kinda complicated, and you’d probably need three RGB-separated filters.

Conceptually, what we’re doing is low-pass filtering, rather than blurring, so I wouldn’t necessarily call filtering just “adding blur”, but in some sense those two ideas are very close to each other, so I wouldn’t call it wrong either. :P The render filtering is a convolution integral, and is slightly different than adding blur to an image without taking the pixel shape into account. Here the filter’s quality depends on taking the pixel shape into account.

You’re right about making note of the animated examples - this is because it’s easier to demonstrate aliasing when animated. The ‘false detail’ is also aliasing, and does arise because the filtering didn’t adequately filter out high frequencies, so they’ve been sampled incorrectly and lead to incorrect image reconstruction. I totally agree that if you get such aliasing false detail, it’s preferable to err (slightly) on the side of blurry, rather than sharp and wrong.

[adastra22]

I don’t know of any display technology in which pixels are little squares, if you really get out the magnifying glass.

[nyanpasu64]

Would DLP projectors which distribute color over time (a color wheel) or multiple light sources combined with dichroic filters, produce uniform squares of color?

[dahart]

In theory if the DMD mirrors were perfect little squares, and if the lens has perfect focus, and if the mirrors switch infinitely fast and are perfectly aligned with the color wheel in time, then maybe it’d be fair to call them uniform squares of color. In reality, the mirrors look square, but aren’t perfect squares - there’s variance in the flatness, aim, edges & beveling, and also both the lens and mirror switching blurs the pixels. The mirror switching over time is not infinitely fast, so the colors change during their cycle (usually multiple times per color of the wheel!) Not to mention some newer DLPs are using LEDs that are less square than DMD mirrors to begin with.

All this comes down to the projected pixels not being nearly as square as one might think (maybe that’s on purpose), though do note that squares are not the ideal shape of a pixel in the first place, for the same reason box filtering isn’t the best filter. If your pixel has sharp edges, that causes artifacts.

Take a look at the pixel-close-up comparisons in the projection shoot-out: https://www.projectorcentral.com/Projector-Resolution-Shooto...

Notice how all of them are visibly blurrier than the source image, and even that all of them have visible aliasing.

Also just for fun, check out this interesting video showing what DMD mirrors look like under a microscope: https://youtu.be/KpatWNi0__o