a try at that Spanish Castle thing

[eub]

(Shocking-to-me perceptual trick ganked from here.)

I gave it a try and mine sort of works; the indefinite persistence is there, but it doesn't manage full color saturation. It might just be my choice of source image. I could try oversaturating my inverse-color image, but it would clamp very soon. I simply set the inverse-color image's luminance to 50% everywhere; I didn't check to see if that's what the "Spanish castle" one did.

What I'm really fascinated by is what characteristic of the grayscale information of the image is needed to make the color afterimage persist. It can't possibly work with a flat gray field, right? But it does work with the castle's sky. So maybe it works with a grayscale gradient, or with a flat area alongside something else in the frame. I should try some of those.

Comments

[beaq.livejournal.com]

The castle image doesn't look any more saturated than yours. And I saw a picture from Arches N.M. that only shows the blue and not the very red color that I know the arch has. Also, I think you can't look directly at the blue area and have it work -- maybe a blind spot issue, maybe something to do with color receptor arrangement?

I think yours works as well as any others I've seen -- it's just the castle has a lot of high-contrast areas, where a little color goes a long way.