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

[eub.livejournal.com]

It's javascript-based (and the js is supposed to preload the images); do you have that turned off?

What's surprising is that the chroma afterimage when fused into the grayscale seems to persist dramatically longer than an afterimage ordinarily does. Then if you shift your point of fixation it breaks and is gone.

[aquaeri.livejournal.com]

I figured some javascript out, but now I've killed the page and I don't want to go back to reloading it (we ate our quota for the month, so no images on the net until Tuesday). So, I didn't get the castle working for some reason, but I did manage to get yours - except I only really got the pink of the flowers on a near-grey background. I think someone else mentioned having a colour contrast pair near the focus spot and I would guess that might help.

I didn't get the afterimage to last surprisingly long. But since a lot of people mention it, I wonder if this combines a normal afterimage colour effect with another one. I can't remember what it's called but I read about it somewhere like Scientific American, I'd guess late 1980s. You'd look at horizontal black-and-magenta stripes and vertical black-and-green stripes, and then when you looked at horizontal black and white stripes, they would fill in with green (and vertical with magenta). It wasn't just afterimage, it'd actually last for up to ten minutes - you could go away and do something else and come back to the magazine and yep, the horizontal stripes still looked greenish. Given the greyscale image used here, it sounds related.

[eub.livejournal.com]

McCullough effect -- pretty amazing thing. When I first tried that (I think the same Sci Am article) it lasted faintly for days; I was afraid I had bent my brain.

This one is related at the very least in that it's got some of the same kind of color/texture "contingency" going on. The thing that first strikes me as different about this one is that the effect disappears and doesn't come back as soon as you break the luma/chroma alignment, whereas the McC effect you can put through the wash with no harm.

[aquaeri.livejournal.com]

It makes sense to me that the McCullough effect (thanks for remembering for me!) would last longer - the stimuli (even width black stripes) is much simpler. You'd be asking whatever part of the brain 'remembers' the green stripes to remember something far more complicated, in terms of colour and placements and shapes. Also, during the "training" part, you're not seeing the black and white part of the pattern, unlike McC.

At least, that all sounds like plausible make-it-up-as-I-go reasoning to me :-).