How to Make Your Own Spooky Magic Eye Pictures (Autostereograms)(blog.demofox.org)
blog.demofox.org
How to Make Your Own Spooky Magic Eye Pictures (Autostereograms)
https://blog.demofox.org/2023/10/22/how-to-make-your-own-spooky-magic-eye-pictures-autostereograms/
83 comments
Yep, I do this too. One thing that's cool is viewing stereograms that have differing colors. Some people apparently can see new colors via this method that is not simply a mix of the two colors.
If this made anyone else curious, I found https://m.youtube.com/watch?v=cQCsDfEqr9o from a post with a ‘blellow’ stereogram https://www.reddit.com/r/MagicEye/s/pd2FtY5PnY
There’s some skeptical commentary in the thread as wel.
There’s some skeptical commentary in the thread as wel.
If I look at that dead center then I get a gradient between the two colors. If I look left or right I get predominantly that color.
Sometimes an inverse gradient will appear and/or it'll shimmer, but I wouldn't say that it's at any time a "new" color.
Sometimes an inverse gradient will appear and/or it'll shimmer, but I wouldn't say that it's at any time a "new" color.
In in astronomy, they used to use a similar technique to 'spot the difference' between photographs of the night sky to find moving objects. They used a special stereo microscope that would place one image in front of each eye. The images were of the same part of the night sky, but separated by time. I saw one recently at the Palomar Observatory.
Here is a more elaborate one from the National Air and Space museum:
https://airandspace.si.edu/collection-objects/microscope-ast...
I even use this technique to find difference of two strings like encoded text, one printed above the other.
Highlights for Children?
Indeed! Great magazine...
I also recall playing a black-and-white space game (top-down scroller) for the original Macintosh where the instructions asked you to tape a piece of cardboard to the middle of the display such that each eye had a separate image of the split screen, which ended up providing a 3D effect without special glasses. I can't seem to recall what the game was, but I could play without the cardboard using the same vision technique (the 3D effect was very pronounced when playing in a dark room).
I also recall playing a black-and-white space game (top-down scroller) for the original Macintosh where the instructions asked you to tape a piece of cardboard to the middle of the display such that each eye had a separate image of the split screen, which ended up providing a 3D effect without special glasses. I can't seem to recall what the game was, but I could play without the cardboard using the same vision technique (the 3D effect was very pronounced when playing in a dark room).
One of my favorite types of Autostereogram is the Object Array Stereogram, because they are well rendered as 2D images, but when you switch to the correct focal distance, you get an amazing 3D experience.
They have the built in constraint that you need to have rows if identical objects, but that works quite well for chess pieces in this example.
https://en.m.wikipedia.org/wiki/File:Chess_Single_Image_Ster...
They have the built in constraint that you need to have rows if identical objects, but that works quite well for chess pieces in this example.
https://en.m.wikipedia.org/wiki/File:Chess_Single_Image_Ster...
I had a (really creative) buddy growing up who figured out that you could do the wallpaper function in Mario Paint (which filled the canvas with repeating icons) and then stamp over some of the icons but slightly offset, and when you crossed your eyes funny they’d pop out of the screen. Very easy DIY Magic Eye.
One of mine is the 3D hologram of yourself flipped upside down, when staring into a curved shaving/vanity mirror at the wrong focal point (i.e. further away than normal). Your eyes receive two images due to focal pont being earlier than expected, and you can resolve them into an (upside down) 3D hologram of yourself!
At first I thought I stumbled onto some clever new hologram tech, though it quickly del apart once I realised that the source image has to already be 3D, and if you can generate an actual 3D image at the source, then you don't really need a mirror to see them...
At first I thought I stumbled onto some clever new hologram tech, though it quickly del apart once I realised that the source image has to already be 3D, and if you can generate an actual 3D image at the source, then you don't really need a mirror to see them...
3D images have captivated me since I was a kid. A frequent source of amusement was the "Victorian wallpaper effect" and even without a viewer I could easily see classic stereo photo pairs in 3D. Not at all difficult to see the "hidden" objects in the article's quite nice illustrations.
While popularity of SIS imagery isn't what it was a few decades ago, programmer interest in the subject has remained quite strong.
As an artist I enjoy incorporating SIS images in my work. In the past I've used a number of open-source SIS generators. Mostly these programs weren't completely satisfactory. A common defect was producing SIS artifacts marring output image appearance.
Subsequently I wrote a SIS program (with GUI for usability) [0] that almost entirely eliminated artifacts in the finished images. Developed with artists' interests in mind, its SIS output looks different vs. examples in the article. (Using depthmap and texture/pattern image inputs, the latter determines the "surface" appearance of the SIS.) However both SIS styles have the same 3D effect capability.
[0] https://thinairarts.com/stereogram.html
While popularity of SIS imagery isn't what it was a few decades ago, programmer interest in the subject has remained quite strong.
As an artist I enjoy incorporating SIS images in my work. In the past I've used a number of open-source SIS generators. Mostly these programs weren't completely satisfactory. A common defect was producing SIS artifacts marring output image appearance.
Subsequently I wrote a SIS program (with GUI for usability) [0] that almost entirely eliminated artifacts in the finished images. Developed with artists' interests in mind, its SIS output looks different vs. examples in the article. (Using depthmap and texture/pattern image inputs, the latter determines the "surface" appearance of the SIS.) However both SIS styles have the same 3D effect capability.
[0] https://thinairarts.com/stereogram.html
> Lastly, I think it would be really neat to make a game that used this technique to render 3d.
See the 1994 game "Magic Carpet" for this and some other weird 3D-modes including an early VR helmet.
edit: the only brief clip I can find online that actually lets you experience the effect:
https://youtu.be/3qiIXbfQjA0?si=NLKv8Bs3EyW-lZX4&t=62
but I did find a modern platformer:
https://managore.itch.io/stereogram
See the 1994 game "Magic Carpet" for this and some other weird 3D-modes including an early VR helmet.
edit: the only brief clip I can find online that actually lets you experience the effect:
https://youtu.be/3qiIXbfQjA0?si=NLKv8Bs3EyW-lZX4&t=62
but I did find a modern platformer:
https://managore.itch.io/stereogram
I once asked a game designer why they implemented autostereograms on Magic Carpet and turns out it was the whim of a programmer :) https://twitter.com/BulkPaint/status/1617192325091819520
Thanks for this. I vaguely recalled reading that Magic Carpet featured a stereogram mode, but then never got around to checking it out.
I remember that the DrDobbs' Journal once featured a stereogram program that ran excruciatingly slow. I wonder how Bullfrog got it performant on the hardware of the era
I remember that the DrDobbs' Journal once featured a stereogram program that ran excruciatingly slow. I wonder how Bullfrog got it performant on the hardware of the era
JITTLOV'S 3-D DOBBS
BOBoBoBoBoBoBOBoBoBoBoBoBOBoBoBoBoBoBOBoBfNoRdBoBOBoBoBoBoBoBOBoBoBoBoBoBOB
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!::::'___`:::::::'___`:::::::'___`:::::::'___`:::::::'___`:::::::'___`::::!
!:::'/_ _\`:::::'/_ _\`:::::'/_ _\`:::::'/_ _\`:::::'/_ _\`:::::'/_ _\`:::!
!:::|/ ~ \|`::::|/ ~ \| `::|/ ~ \|' `|/ ~ \|::' |/ ~ \|::::'|/ ~ \|:::!
!:::|'-.-`| :::|'-.-`| :|'-.-`| |'-.-`|: |'-.-`|::: |'-.-`|:::!
!:: (|e|e|? ::(|e|e|? ' (|e|e|? ` ' (|e|e|? ` (|e|e|?.: (|e|e|? ::!
!. `._^_,'' :`._^_,'..' `._^_,'`...'`._^_,' `..`._^_,'. ``._^_,' .!
!. \\=// \\=// \\=// \\=// \\=// \\=// .!
: U/_/ U/_/ U/_/ U/_/ U/_/ U/_/ :
@/ \&~ @/ \&~ @/ \&~ @/ \&~ @/ \&~ @/ \&
Y/\.::./\S\ /Y/\.::./\S\ /Y/\.::./\S\ /Y/\.::./\S\ /Y/\.::./\S\ /Y/\.::./\S
E$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$E
%%%%XX%%%%%%%%%%%XX%%%%%%%%%%%XX%%%%%%%%%%%XX%%%%%%%%%%%XX%%%%%%%%%%%XX%WiZ
These things never worked for me. Maybe I don't understand how to look at them correctly to get whatever 3D effect they're supposed to make, but for the life of me, I could never see anything at all in those patterns, neither on screen nor when printed.
edit: I found this video[1] with pairs of images that tells you to hold sunglasses in front of your right eye if you can't defocus your vision correctly. This worked for me with an ND filter, it really feels like it shouldn't do anything but I did see depth. Those patterns though, still no idea how to make them work.
[1] https://www.youtube.com/watch?v=mLsODo7ycaA
edit: I found this video[1] with pairs of images that tells you to hold sunglasses in front of your right eye if you can't defocus your vision correctly. This worked for me with an ND filter, it really feels like it shouldn't do anything but I did see depth. Those patterns though, still no idea how to make them work.
[1] https://www.youtube.com/watch?v=mLsODo7ycaA
https://hidden3d.com/howto-view-stereograms/
It lists multiple methods along with an "easy" stereogram to view. Maybe one of them works for you, it worked for me.
edit: I don't see it mentioned on the page, but in my experience the absolute size of the image matters. It works better on a computer monitor for me rather than a smartphone screen. Play with zoom levels.
It lists multiple methods along with an "easy" stereogram to view. Maybe one of them works for you, it worked for me.
edit: I don't see it mentioned on the page, but in my experience the absolute size of the image matters. It works better on a computer monitor for me rather than a smartphone screen. Play with zoom levels.
TBF, these "hidden" autostereograms are the most challenging to "see" - it's probably better to start off with two "actual" pictures printed or displayed side by side (because there you have some cues to how far you are from the images overlapping), and then try to apply the same technique to autostereograms? I can manage to do it most of the time, but it always takes some effort. I think it also helps if the image is bigger, but YMMV...
I can't see them either. I defocus to get the the dots to come together and I end up not seeing:
* * *
but instead:
* *
* * *
but instead:
* *
* *
I get your example too if I tilt my head. Can you tilt your head to correct for it?
Same for me, I can't see anything in those images. I have astigmatism and red/green colorblindness though (which I discovered later in life). Could be related?
I have astigmatism as well and it initially took me a very long time to manage to see them, it might be that it has an effect
(I practiced enough that I then learned to see them at a blink of an eye, and it helped my normal vision a lot btw)
I used to have really bad myopia, but right now, many years after laser surgery, I still have nearly perfect vision. I feel like my main problem is that I can't overcome my reflexes.
A technique I've seen is that you put a reflective transparent surface in front of the autostereogram and gaze at your own reflection. This puts your eyes at the right focal point.
I've been pretty good at seeing these in the past, but I had no luck with the images in the article.
I've been pretty good at seeing these in the past, but I had no luck with the images in the article.
Actually I can also see this one, maybe becoase of the 3d cube at the beginning that exactly shows you what to do.
Now I will probably see everything blurred for rest of the day.
Now I will probably see everything blurred for rest of the day.
https://managore.itch.io/stereogram is an impressive example of the possibilities here, with an animated noise image and interactive depth map.
I find these much easier to work on my eyes than the one posted on the article above, probably because the side by side pattern is easier to cross-focus.
This was interesting.
Stereo wideners (a switch made to cause music to sound wider in audio 3D space) work very similar to the Dolby3D, except with equalization instead of colour filtering.
Dolby3d takes chunks of red, green and blue, and filters them so the left and right eye are seeing slightly different reds, greens and blues in a way that isn't easily detected by the person viewing them. Both eyes see apparently normal views, but together they see a stereo image.
Stereo audio wideners take a set of audio frequencies, lowering their EQ on one side while raising them an equivalent amount on the other, so that the left and right ears are hearing different equalization that still sound reasonably normal.
It makes sense that Dolby is the primary name associated to both technologies. They are pretty much the same left-right reversed comb filters, except light frequencies versus sound frequencies.
Stereo wideners (a switch made to cause music to sound wider in audio 3D space) work very similar to the Dolby3D, except with equalization instead of colour filtering.
Dolby3d takes chunks of red, green and blue, and filters them so the left and right eye are seeing slightly different reds, greens and blues in a way that isn't easily detected by the person viewing them. Both eyes see apparently normal views, but together they see a stereo image.
Stereo audio wideners take a set of audio frequencies, lowering their EQ on one side while raising them an equivalent amount on the other, so that the left and right ears are hearing different equalization that still sound reasonably normal.
It makes sense that Dolby is the primary name associated to both technologies. They are pretty much the same left-right reversed comb filters, except light frequencies versus sound frequencies.
The images he chose have too much fine detail. That makes it very hard to identify what they are even when you "get" the effect.
I always find this to be common problem with magic eye pictures. The 3D effect is interesting to experience, but the pattern is so busy and distracting that it's often hard to tell what the object is supposed to be anyway.
As a kid I had a book which had tried to address this problem. The shape was still hidden but certain elements of the repeating pattern coincided with and emphasized parts of the hidden image - but in a way that wasn't obvious until you had revealed the 3D effect. It was partially successful.
As a kid I had a book which had tried to address this problem. The shape was still hidden but certain elements of the repeating pattern coincided with and emphasized parts of the hidden image - but in a way that wasn't obvious until you had revealed the 3D effect. It was partially successful.
Does the effect work with an animated depth image?
I always have a hard time with these. I get the 3d effect but can never figure out the image. I suspect based on reading some theory that I am viewing them cross eyed instead of slack eyed. But have no idea how to do it the other way around.
Update: it does, I found a youtube video, still cant resolve it however. https://www.youtube.com/watch?v=IZpsbQMQFBs
I always have a hard time with these. I get the 3d effect but can never figure out the image. I suspect based on reading some theory that I am viewing them cross eyed instead of slack eyed. But have no idea how to do it the other way around.
Update: it does, I found a youtube video, still cant resolve it however. https://www.youtube.com/watch?v=IZpsbQMQFBs
I have always crossed my eyes since the days of Magic Eye books, and could reliably "see" the image but it was always reversed (seemingly going INTO the page). It wasn't until this article that I realized I could go "slack eyed" as you call it. Now the images pop OUT of the page instead of recede into it. I wish I could rewind 30 years and tell my younger self how to do it.... I would have enjoyed those books so much more.
Linked video - these are some of the coolest I've seen in a long time: https://www.youtube.com/watch?v=NmRfVoiFDu4
The almost holographic looking sphere and pyramid at 00:15 seconds.
The nested petal thing at 45 seconds.
The Yin-Yang at 01:22
Here's soem cross-eye autostereo drone videos: https://www.youtube.com/watch?v=QzyjLtzPDNw
The almost holographic looking sphere and pyramid at 00:15 seconds.
The nested petal thing at 45 seconds.
The Yin-Yang at 01:22
Here's soem cross-eye autostereo drone videos: https://www.youtube.com/watch?v=QzyjLtzPDNw
This is a good one — probably came up on an earlier HN post:
https://youtu.be/2AKtp3XHn38?si=GDHjv1VyxCvMAzQU
https://youtu.be/2AKtp3XHn38?si=GDHjv1VyxCvMAzQU
The video just animates the surface picture, and swaps between different depth maps. But otherwise the depth maps are not animated, alas.
This one https://managore.itch.io/stereogram (link from another comment) actually animates both.
This one https://managore.itch.io/stereogram (link from another comment) actually animates both.
Thanks for sharing that video, worked perfectly for me. Although watching videos with this effect is kinda headache inducing after a while, at lesst for me.
I can never see it for some reason. I assure you I just saw the eye doctor and my eyes were also fine 20 years ago when these were popular.
They were always a lot easier to see framed so you could trick your focus by looking at reflections in the glass. Ideal conditions: printed at poster size, at a shopping mall kiosk, near a trashcan with an ashtray.
I have ~-1.75 in one eye and -3.5 in the other and it took me a long time to eventually be able to resolve the hidden images. They usually aren't all that satisfying really.
The fact that all you need is a depth map of what you'd like to create makes me wonder if anyone's ever linked something like this up to a video game engine to make possibly the least visually pleasing and least accessible game out there.
Yep, ZeroGravitas mentioned Magic Eye in another comment, also this:
https://www.rockpapershotgun.com/cross-your-magic-eyes-to-pl...
https://www.rockpapershotgun.com/cross-your-magic-eyes-to-pl...
This was done with Doom!
https://www.pcgamer.com/omdo-is-what-happens-when-you-turn-d...
https://www.pcgamer.com/omdo-is-what-happens-when-you-turn-d...
Call it Polybius.
I can only see these dumb things in reverse (the shape is always sinking into the page, rather than popping out). isn't there a way to generate these inverted so weirdos like me can finally enjoy them ?
You're crossing your eyes instead of distancing them, that's a lot easier for me as well but you should manage to see these kind if stereograms too with some practice.
Simply letting your sight defocus as when you're looking into the void thinking something will probably get you closer; then keep in mind that to see these images you need to make a much more subtle correction than when doing the cross-eyes thing, such that it's actually easy to "bind" to pairs of patterns farther apart than what's needed.
The rest is just like with cross-eyes stereograms, check the borders of the double-image to verify the alignment of your head, and as you get closer to joining the dots strive to get the image back in focus (but of course without moving the eyes).
Simply letting your sight defocus as when you're looking into the void thinking something will probably get you closer; then keep in mind that to see these images you need to make a much more subtle correction than when doing the cross-eyes thing, such that it's actually easy to "bind" to pairs of patterns farther apart than what's needed.
The rest is just like with cross-eyes stereograms, check the borders of the double-image to verify the alignment of your head, and as you get closer to joining the dots strive to get the image back in focus (but of course without moving the eyes).
I've read other answers here to that effect...I was trying more the other night to do other kinds of things with my eyes but the hole inside the image kept popping "in" even when I wasn't trying to do anything in particular. Might just be my physiology crossing my eyes all the time anyway
Well you've maybe become used to it now, so it's even harder to switch to the straight-eyes technique
Can anyone else not see the image?
I can unfocus my eyes a little, but what I think is mostly happening is that I’m just slightly crossing my eyes so it doesn’t work.
Is it better on a non-phone screen?
Is it better on a non-phone screen?
Crossing the eyes tends to show just the outline of the shape instead of a 3D image.
The phone screen works fine for me, but a larger screen might work better for you. It's more like a "zoning out" unfocusing than a crossing of the eyes, like you're trying to look at a point slightly behind your screen.
The phone screen works fine for me, but a larger screen might work better for you. It's more like a "zoning out" unfocusing than a crossing of the eyes, like you're trying to look at a point slightly behind your screen.
Yes, a bigger screen helps a lot. There are a bunch of tutorials how to get it to work on youtube etc.
for those who can master it, here is Tetris to play: https://www.deviantart.com/3dimka/art/3D-Stereogram-Tetris-3...
I was never able to see stereograms, the most I was able to pull out was to see it inverted (x seeing with eyes, while the opposite is required).
I was never able to see stereograms, the most I was able to pull out was to see it inverted (x seeing with eyes, while the opposite is required).
Fun, but extremely unpleasant. The more stressed I get the more difficult it is to relax my eyes and see the pattern.
I'm not an expert but I don't think you need to go to a doctor if you can't see them easily, I think it's common for it to take a lot of effort initially
It actually might well be that people with sight problems will have a harder, or a lot harder, time at first, but, yeah, with enough time most will probably manage to.
I think it took me weeks to start to see them easily, and probably at least days to see one for the first time.
By the way, from then on though, I became able to e.g. watch stereo videos stereographically in a split second, from any position (so long as I kept exercising every once in a while); so it's probably just a matter to learn how it works and maybe exercise the eyes a little, for most people.
It actually might well be that people with sight problems will have a harder, or a lot harder, time at first, but, yeah, with enough time most will probably manage to.
I think it took me weeks to start to see them easily, and probably at least days to see one for the first time.
By the way, from then on though, I became able to e.g. watch stereo videos stereographically in a split second, from any position (so long as I kept exercising every once in a while); so it's probably just a matter to learn how it works and maybe exercise the eyes a little, for most people.
Yup. I'd compare it to learning to whistle or roll your r's.
Some people can't do it ever, some people do it effortlessly on the first try, and the rest of us are baffled for hours/weeks/years until we randomly figure it out and it clicks.
It's just certain bodily movements that can be extremely non-intuitive. Consciously moving your eyes apart is one of them.
Some people can't do it ever, some people do it effortlessly on the first try, and the rest of us are baffled for hours/weeks/years until we randomly figure it out and it clicks.
It's just certain bodily movements that can be extremely non-intuitive. Consciously moving your eyes apart is one of them.
[deleted]
This was the first time I’ve ever seen these. Thanks for the walkthrough. When I was in grad school I remember these books and all the freshman who could see them telling me I had wrecked my eyes from spending countless hours in the computer lab. They weren’t wrong but I pretty much gave up until seeing progressive refinements in this tutorial. Very cool!
I can only really see these things crossed instead of parallel… makes all of these push into the screen instead of jump out.
Nice, but I still like making red-cyan anaglyphs
https://en.wikipedia.org/wiki/Anaglyph_3D
though I think the premium way to enjoy stereograms in 2023 will be with a VR headset (no fan of Facebook but I just got a Quest 3 and wow!)
https://en.wikipedia.org/wiki/Anaglyph_3D
though I think the premium way to enjoy stereograms in 2023 will be with a VR headset (no fan of Facebook but I just got a Quest 3 and wow!)
Unfortunately they are hardly making stereoscopic movies anymore. Maybe they come back with VR though (doubt it).
Stereoscopic movies have some fundamental problems. I think about 20% of people have impaired stereo perception and don’t really get anything out of them. That’s not so bad, but maybe 8% or so of people are made uncomfortable by stereo movies.
The consequence of that is that movies can’t go 100% to stereo. So they are left with the strategy of showing the movie in two theaters and charging a few $ more for the stereo version which (1) alienates consumers who think it’s just a greedy “money grab” but (2) would usually cost money instead of make money because of the expense of having more showings that will be less well attended except in the case of the absolutely largest movies that can support a large number of showings.
The consequence of that is that movies can’t go 100% to stereo. So they are left with the strategy of showing the movie in two theaters and charging a few $ more for the stereo version which (1) alienates consumers who think it’s just a greedy “money grab” but (2) would usually cost money instead of make money because of the expense of having more showings that will be less well attended except in the case of the absolutely largest movies that can support a large number of showings.
I somewhat doubt one can really get uncomfortable by stereo movies. The real world is in stereo after all. That's like becoming uncomfortable from watching a color movie. The reason they show two versions of a movie seems to me more likely for the opportunity to charge more for people who care about 3D, and less for people who don't want to spend too much.
Well, there's always porn. They are always on the forefront of technology.
The haunted house one faked me out. I thought I was looking at https://davematthewsband.com/music/remember-two-things-reiss...
The blue noise example is crazy. It's always been trivial to me to cross-eye into MagicEyes, I can even comfortably scroll the page and never lose the 3D. I had no idea there were (if I understood correctly) adversarial background patterns.
Interestingly, perhaps, I found that one to be easier to make out the fine detail than any other magic eye that I've seen before. However I did find it a bit more eyestrain inducing as well. This is a great blog and makes me want to experiment more.
You mean that you do see the 3d effect in the blue noise image???
Hmm... I do see it, but when I left my comment last night it would seem I had been looking at the grayscale version of the color noise image by mistake. I can still make it out in the blue noise image but it's quite a bit more eyestrain-inducing.
The grayscale version is indeed the clearest, for the blue noise instead I suspect that it's impossible to see the 3d effect, maybe because the pattern is too dense and regular
That's why I'm surprised if you do see it
That's why I'm surprised if you do see it
Not GP, but I can see. Not comfortably though and my eyes want to refocus so I have to expend conscious effort to keep looking at it - unlike most other stereograms where once locked in the effect remains almost effortlessly.
All that is old is new again. I remember figuring out how to make random dot stereograms shortly after they first appeared in the late 1980s.
I recall it taking several seconds just to generate the random dot map on my 4.77MHz XT.
I recall it taking several seconds just to generate the random dot map on my 4.77MHz XT.
First I thought…crap I need to go see an eye doctor, then booom. The depth kicked in. My eyes got stuck lol. Trippy. Live the effect.
Fractint was an excellent program for making Stereograms, and I believe it can still be used for that task.
Wow, now that I need reading glasses these are easier than when I was a kid
Hyper Color tshirts reminded us we all had nipples and sweaty armpits.
My eyes have never been so itchy, thank you.
1990s were fun times!
My trick was based on "magic eye" images I used to enjoy. When I saw the side-by-side drawings used by the puzzle, I wondered what would happen if I "fuzzed" my eyes as if I was looking at a magic eye photo. To my surprise, all of the items that were different between the two images "vibrated" or "shimmered", while the rest of image stayed steady. I repeatedly fuzzed and focused to spot all the differences in a matter of seconds.