ROTSPRITE, useful tool

[QuaziGNRLnose]

well i do pixel animations sometimes, and nothing is more annoying than dirty rotation tools, when your using rotation to speed things up, either its puts AA everywhere, that you dont want, or it just messing everything up, even if it doesn't add new colours. i was on Wikipedia and i found this when looking at sprite scaling algorithms.



heres a picture of the rotation in action, the first image, non rotated, the second, badly rotated, the third, with rotsprite
as you can see it does a beautiful job, adds no new colours, and im sure some animators who make use of rotation would love it, since it barely needs clean up work.

RotSprite is a scaling and rotation algorithm for sprites developed by Xenowhirl. It produces far fewer artifacts than nearest-neighbor rotation algorithms, and does not interpolate or anti-alias, so it does not introduce new colors into the image.[6]
The algorithm first scales the image to 8 times its original size with a modified Scale2x algorithm which treats similar (rather than identical) pixels as matches. It then calculates what rotation offset to use by favoring sampled points which are not boundary pixels. Next, the rotated image is created with a nearest-neighbor scaling and rotation algorithm that simultaneously shrinks the big image back to its original size and rotates the image. Finally, overlooked single-pixel details are restored if the corresponding pixel in the source image is different and the destination pixel has three identical neighbors.[7]

an excerpt from wikipedia ^

http://info.sonicretro.org/RotSprite

[Arne]

I experimented a lot with this a few years ago, although I scaled up a few times and cleaned up by hand and then drew down scaled in-engine (games can easily do this on the fly). I suggested it for Cortex Command but we ended up not doing it.

Another thing I experimented with was sampling a couple of pixels rather than just one (crisp) or all (blur).

Mipmapping is another technique that works well, because sampling a small blurry image (at a distance) results in less flicker (more representative sample points).

[QuaziGNRLnose]

im curious, does cortex command use per-pixel sampling for its rotation or something else/similar?, from what i remember it was quite well done even in the early demo i have.

[Arne]

I think it uses plain unfiltered 1x rotation. Pieces of junk are of course irregular with all sorts of angles, but since it's already noisy junk, rotation doesn't hurt much. For weapons and other stuff, a lot of 90 degree angles are used and those survive rotation pretty well. Also, since the things move a lot, some of the ugly rotation artifacts are averaged out.

Raiden II looked pretty good even though it used unfiltered rotation. I think it used a lot of 90 degree angles too.

[EyeCraft]

Wonderful, I did not know about this. Will no doubt find use for it, danke!

[Mathias]

Yes, this is awesome!

[st0ven]

im quite a fan - wondering how amazing it would be with a more proper ui and some batch processing capabilities <_<  >_>

[Pawige]

I just wish this was built into Graphics Gale or Promotion. Oh man...That would rock so hard. Barring that, what st0ven said. I've used it so much since I got it! Great tool.

[alspal]

Yeah I'd love to see this part of graphics gale or something.

[Ai]

Integration in any app would require a reference implementation, for a start.
The exe is not sufficient.

Since it's an exe, I want to make my own implementation anyway (Running windows stuff in linux is a bit awkward).
The following parts of the description are not precise enough, IMO:
"It then calculates what rotation offset to use by favoring sampled points which are not boundary pixels."
(are we talking about what position to treat as the image centre?)

"Finally, overlooked single-pixel details are restored if the corresponding pixel in the source image is different and the destination pixel has three identical neighbors."
('single-pixel details' isn't really well enough defined here. Isolated single pixels? single pixels terminating a line? single pixels comprising a 1pix-thick line?)

Though his last activity on that site was in 2007, I'm hoping to get some more specifics out of Xenowhirl.