SarahJun 7
Danpiker

This illusion was new to me. Does whichever dot you look at turn more purple?

Pretty neat how clearly this lets you see the reduced sensitivity to blue light in the very centre of your vision.

https://www.schulz-hildebrandt.com/9-purple-dots-illusion/

https://arxiv.org/abs/2509.11582

Jun 7 at 12:12pmWeb
Show threadConchoidJun 7
@Danpiker i don't see it
Show threadTrickpawJun 7
@conchoid @Danpiker this has never worked for me either!
Show threadThe Sleight Doctor 🃏🍉Jun 7

@Pikestreet @conchoid @Danpiker Nor me. I have a collection of optical illusions that do fool me though!

Lemme find them...

Show threadThe Sleight Doctor 🃏🍉Jun 7

@Pikestreet @conchoid @Danpiker

This is a good one.

Show threadThe Sleight Doctor 🃏🍉Jun 7

@Pikestreet @conchoid @Danpiker

This is also a good one.

Show threadDog Noise GeneratorJun 8
@ApostateEnglishman @Pikestreet @conchoid @Danpiker that image should prob have a content warning! Its quite a strong vestibular stimulus. I felt motion sick just seeing for a few secs.
Show threadTrickpawJun 7
@ApostateEnglishman Lots of them work on me, just not this one for some reason!
Show threadThe Sleight Doctor 🃏🍉Jun 7

@Pikestreet This one really bends my tiny mind!

It's not a spiral, but perfect concentric circles. 🤯

Show thread🍋 Superball ☀️Jun 8

@ApostateEnglishman

🤯 Even with your preface, I still questioned it! That’s wild! 😵‍💫

@Pikestreet

Show threadJohn Maxwell6d ago
@ApostateEnglishman No, it's not circles! It's a spiral, that is rotating! Actually rotating at the exact same speed as my eye is moving around the perimeter! I'm sure of it.
Show threadThe Sleight Doctor 🃏🍉6d ago
@jmaxsfu We are all sure of many things. 🤷🏻‍♂️
Show threadVive LevantJun 8

@ApostateEnglishman @Pikestreet @conchoid @Danpiker did you, as I did, try to experience it during an insomnia at 4 am WHILE THE BLUE LIGHT FILTER OF YOUR PHONE’S SCREEN IS ON ?

Honestly I realized it when by day the illusion worked for me contrary to the middle of the night.

In French we have a saying that at night every cats are gray, similarly, at night, every dots are purple.

Show threadNatanox 🇺🇦🇵🇸2d ago
@ApostateEnglishman @Pikestreet @conchoid @Danpiker Are you all sure? I noticed this illusion is highly depending on screen distance and size of the picture (so often works worse on Smartphones). If the dot is too big or the screen too close to your face your eyes may get enough information and make the dot blue, but once you change size/distance the dot turns purple as your eyes lose the necessary info to offset it.
Show threadDanpiker2d ago
@Natanox @ApostateEnglishman @Pikestreet @conchoid It's definitely screen dependent, and not just because of the size. On my desktop monitor the effect is completely absent for me, while on my phone it is very strong, even at a distance where they are the same apparent size.
Show threadderptronJun 7

@conchoid @Danpiker I had to work pretty hard at it.

I had to open the many dots image alone and zoom in. Then if I stare at a dot really hard it does appear to be ever so slightly darker a purple than the rest.

My eyes hurt now and everything is blurry. Don't do this at home.

Show threadDgarJun 7
@crazyeddie @conchoid @Danpiker
*only do this at home.
Show threadFediThing Jun 7

@crazyeddie @conchoid @Danpiker

Weirdly it worked better for me when the image was small in my timeline, the purple was much clearer, and zooming in made it less clear. I guess different people's brains have slightly different perceptions?

Show threadTrueNorthSpice 🇨🇦Jun 7

@conchoid @Danpiker

Me either.

Show threadJean-Baptiste FidéliaJun 7
@conchoid @Danpiker that's interesting. What do you see exactly when you look at it? What colors do you see? I'm curious.
Show threadConchoidJun 7
@jeantranscene @Danpiker
Grey-blue-ish background and blue dots. On a computer screen, but the screen is not that bad. Also don't know about color vision impairment to have.
Show threadjakllschJun 8
@conchoid @Danpiker It worked for me on a AMOLED phone, but didn't work for me on a IPS LCD laptop.
Show threadMarcin WicharyJun 7
@Danpiker Oh, wow. It does, and incredibly quickly and intensely, too.
Show threadIgnorePriorInstructionsJun 7
@mwichary @Danpiker Same. My experience is super trippy, close or far. The effect is immediate and distinct when I move my eye. Could be all that time staring at the sun.
Show threadotackeJun 7
@Danpiker Where is the :hover pseudo-class set? 😅
Show threadgroxxJun 7
@otacke @Danpiker foveated css 
Show threadPass the DutchieJun 7
@Danpiker
Cool! Thanks for this.
I recently watched a YT short on color theory. That was insightful and interesting.
Show threadCubeJun 7
@Danpiker holy moly that's an incredible effect
Show threadBørgeJun 7
@Danpiker This is trippy as hell! I also feel like the border is more distinct when it's purple, but I can't really check because they all turn purple when I look at them! 🤯
Show threadBørgeJun 7
@Danpiker OK, so now, looking at it on my phone, they're all purple! And the one I look at is only slightly darker purple. Wild stuff. 😅
Show threadD. G. MarshallJun 7

@Danpiker

Yes. Whichever dot I focus on turns purple.

Show threadKid ManiaJun 7
@davidtheeviloverlord @Danpiker
Same.
Show threadDavid P5d ago

@clintruin

If I focus on midpoints between dots, the two of them go purple! Cool.

@davidtheeviloverlord @Danpiker

Show threadChris Ford Jun 7
@Danpiker Not at first, because I was wearing yellow-tinted sunglasses. When I took them off yes.
Show threadMrBlubberJun 7
@Danpiker Fascinating! If you force your focus slowly moving towards a circle you can even get a gradiant.
Show threadArneBabJun 7
@Danpiker That’s neat! thank you!
Show threadRandall LeeJun 7
@Danpiker Holding my phone at arms length all of the dots are purple.
Show threadDaniel BohrerJun 7
@Danpiker interestingly it works better for me on the smaller thumbnail than on the full version of the image
Show threadAmy de BuitléirJun 7
@Danpiker For me, the dot that I'm looking at doesn't change, but the remaining dots fade into the background.
Show threadAmos MulderJun 7
@mhwombat @Danpiker Interesting, I see both effects.
Show threadPasswordsarehard4Jun 7
@mhwombat @Danpiker mine as well. Eventually even the center dot disappears and it’s just a hazy purple background.
Show threadPhilSalkieJun 7

@Danpiker

Have a look at:

https://gamesx.com/misctech/visual.htm

Your eyes have much lower resolution in blue light than in red or green, the article demonstrates that increasing the size of the blue pixels by 9 times (3x3) makes an almost imperceptible change in the image. Link rot has taken the extra images and a diagram showing a proposed pixel layout of a big blue diamond surrounded by small red and green squares.

Human Visual Accuity: Your Eyes Suck at Blue

Human visual accuity in Blue

Show threadElio CampitelliJun 7
@PhilSalkie @Danpiker Huh. Does this means that we shouldn't be writing small text or rendering small details in blue?
Show threadPhilSalkieJun 7
@eliocamp @Danpiker
It probably means not just that but we should be compressing the blue layer much more than the green or red when doing lossy compression algorithms.
Show threadgroxxJun 7
@PhilSalkie @eliocamp @Danpiker rgb565 is a somewhat common color mode for this reason - we see green with the most detail, so when you're looking to reduce bits per pixel it makes sense to cut the other two slightly
Show threadPhilSalkieJun 7

@groxx @eliocamp @Danpiker
Makes sense, there are a number of monochrome photosensors designed to work near the center of the green visual peak as well.

What I found interesting was not just being able to decrease the number of bits of blue intensity for each pixel, but making the pixel count so much less for blue. We've reached a point in tech where speaking about "efficiency" marks you as being from a bygone age - but this seems like it could be a neat way to pack more images into fewer bytes.

Show threadgroxxJun 7
@PhilSalkie @eliocamp @Danpiker yea, I can't find the blog post I vaguely remember from long ago that had samples of all channels, but https://calebkruse.com/10-projects/seeing-blue/ looks like a decent demo near the bottom. it's kinda crazy.
Caleb Kruse - Focusing on Blue

Show threadElio CampitelliJun 8
@groxx @PhilSalkie @Danpiker That's quite dramatic
Show threadRémi LetotJun 7
@Danpiker
Amazing, I feel like my smartphone can track my eyes 😃
Show threadHowToPhil (Phillip R)Jun 7
@Danpiker It turns... a slightly darker blue, I think?
Show threadcherieherrjonesJun 7
@Danpiker I definitely see it. Very cool!
Show threadAxel HartmannJun 7
@Danpiker - where to use?
guest bathroom wallpaper or <insert evil laughter> tablecloth
Show threadAxel HartmannJun 7
@Danpiker or: legal texts
Show threadBytebro 🇬🇧 🇺🇦 🇬🇱Jun 7

@Danpiker

Doesn't seem to 'work' for me. I have no colour blindness of which I'm aware!

Show threaditgrrl Jun 7

@Danpiker

a #ProTip for those playing along at home – if you have “night shift” (iOS) or “eye comfort” (Android) on you’ll probably need to turn it off to see the effect, otherwise all the dots will just look purple 💁‍♀️

Show threadTrueNorthSpice 🇨🇦Jun 7

@itgrrl @Danpiker

Using my laptop with no night mode or colour blocking, it doesn't work for me. Maybe some brains are wired differently.

Show threadSolithaJun 7
@TrueNorthSpice @itgrrl It can be about your electronics, too. I can see the effect on my new monitor, but not on my old one.
Show threadTrueNorthSpice 🇨🇦Jun 7

@solitha @itgrrl

You may have a valid point, my laptop is 14 years old

Show threadDan SandlerJun 7

@Danpiker what's fascinating about this is that, as someone with deuteranomaly, _none_ of the dots is obviously purple for me, on any background. they all seem "blue, but if you told me they're actually purple, I would believe you", which is just really common for me.

that must mean that the amount of short-wavelength sensitivity loss in the fixated area is not enough to offset the confusion (and overall lower information content) of overlapping long/medium wavelength response?

Show threadBill, organizer of stuffJun 7
@Danpiker TIL (from someone who said "this doesn't really work") - this doesn't work if your phone has a blue-light-blocking filter on it!
Show threadderptronJun 7
@wcbdata @Danpiker Using a laptop. Yoga 910. Quick duck search leads me to believe there's no such filter on its screen. My night light shift software isn't on.

vOv