

Optical illusion of motion - Uncle_Sam
http://www.youtube.com/watch?v=AMzuu6Bl2jQ&feature=player_embedded

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qwzybug
There are a few of these (or similar) on display at the San Francisco
Exploratorium; well worth a visit if you've never been.

I made a simple RMagick script to generate these from animation frames. Turns
out it even works well with full-color images. See:
<http://doormouse.org/illusion/> (interactivity only works in browsers that
support the HTML5 range element)

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ryanpetrich
Clever, though I don't consider this an optical illusion any more than I
consider a TV/monitor one.

~~~
teaspoon
Agreed; it's exactly the same principle as a flipbook or movie projector.
Though it seems arbitrary that those things have ceased to be seen as optical
illusions.

~~~
Retric
The reason IMO it's more an optical illusion is your brain extrapolates it as
"_ behind a fence" even though you know it's just some funny lines behind the
screen. 90% of the background image is blocked but you easily block out all
the vertical lines and just see the object behind the fence.

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chip
A tutorial here:
[http://blog.makezine.com/archive/2010/01/updated_animated_op...](http://blog.makezine.com/archive/2010/01/updated_animated_optical_illusion_t.html)

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rev087
I wonder what would be the outcome of making a small version of that trick in
a business card...hmm...

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raimondious
This technique, used with space between the grating and the image, is what
they are using for glasses-free digital 3D screens. You could think of this as
a completely flat parallax barrier screen, only it's physically moved to show
different views of the image. Autostereoscopy works because the angle of your
two eyes does the moving for you (there are only two frames — one for the left
eye view and one for the right eye view).

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bmalicoat
That was pretty cool. I wonder how they make the images, by hand or some
automated algorithm that takes a few-framed movie and prints it up.

~~~
teaspoon
It's a simple algorithm, and you could carry it out by hand in an image editor
without much difficulty.

Just overlay N layers (the frames of your animation) on top of one another.
For every Nth column of pixels, delete the next N-1 columns following it (in
all layers). Then, for each layer at index X in the stack, translate the
entire layer horizontally by X pixels.

Your overlay for viewing the animation is just a black opaque rectangle with
every Nth column being deleted to reveal the image beneath.

~~~
LarrySDonald
Looking at it, yes, that's pretty much it. Lenticular images (aka, sports
flips, those odd things that move when you tilt them, etc) are based on the
same principle except with a lens to show each "band" depending on viewing
angle rather then moving a striped sheet over it to obscure a sequence of
frames.

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nazgulnarsil
similar to walking past a slat fence and yet seeming to have an uninterrupted
view of the yard as long as you're moving.

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bliss
This is giving me happy memories of demos on the commodore Amiga and Atari ST
:-)

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est
startup idea: make advertising board with this. People walk by and see the
motion.

~~~
TheSOB88
The "fence" part has to physically move. What you are describing - no moving
parts required - is basically a hologram.

~~~
devinj
Eh? It only has to move relative to the image behind it. Parallax should do
the work here.

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TotlolRon
Interactive version here: <http://blogoscoped.com/files/stripes.html>

~~~
samratjp
So much more realistic this way. Thanks for the share :-)

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tumult
Hacker News?

First person who says "HEY BUT ITS HACKIN UR VISION" gets a fist sandwich.

~~~
rewind
Seriously, why bother then? Keep your fist sandwich to yourself.

~~~
tumult
There's no tagging or categories on HN, so it's getting more and more
difficult to skip past all of the chaff coming through.

~~~
rewind
Your response is pointless. Just flag it and move on. Your fist sandwiches
should be reserved for people who waste comments saying things don't belong on
HN. No tagging or categories does not mean that type of comment is a helpful
alternative. It's worse.

~~~
tumult
I don't know why you think my comment is supposed to be an alternative to
something. What is your comment supposed to be an alternative to? My comment?
Huh?

I'm specifically trying to discourage the original submitter from putting off-
topic material on HN. There are plenty of sites that cater to whatever stuff.
I realize there is a gray area and this argument has been rehashed countless
times, but come on, this is irrelevant in every single way.

~~~
samratjp
Please refer to <http://ycombinator.com/newsguidelines.html> for "gray area."

~~~
tumult
Yeah thanks, never seen that before. Buzz off.

Feel free to ding my karma again, I have plenty. Might as well put it to use
griping about the same people who will vote these comments down. If nobody is
afraid to break the HN taboo of complaining about the quality of submissions
("oh he's complaining, he must be a new guy, haha I'll link him to the
guidelines and put him in his place, yeah!") then people will keep submitting
crap.

~~~
samratjp
I didn't want to reply to throw fuel in this flame, but felt that I should put
an end to it. I merely pointed out the link (which you already are familiar
with) to end the flames that were going on. Fwiw, I didn't even ding your
karma down.

Yes, any community will inevitably be filled with a few neighbors with lawn-
mowers going off in the middle of the night, but it's worth a gentle reminder.
Heck, yes this may very much be off topic (to you and some others), but you
have to also realize that the community shapes up the discussions. In this
very thread, there are discussions about how this could be done interactively
and even some examples at that too.

And before I upvote or downvote, I look at the username, their recent actions
and their karma level. I saw the post user's profile and learned that the user
is new to this community and let it slide, for hey we were all noobs once here
and have probably done some off-topic things.

"people will keep submitting crap." Oh yes, they will! But, don't worry, HN is
a pretty good community as a whole at smelling out B.S. :-)

~~~
tumult
Sorry, I didn't mean to imply "you" specifically as the one dinging my karma.
I kind of meant for everything after that first sentence that referred to
"you" to mean anyone reading it. You can't vote down all of my comments 5
times on your own.

For what it's worth, I'm mostly disappointed in stuff like this because, while
many people were noobs at some point: 1) anyone is free to lurk until they
feel un-noob-like 2) you can show some restraint when posting links.

I've only made a few submissions, and I think they were pretty ok. Out of the
10, 1 was off topic, and only partially.

Here is what bugs me the most: I used to be able to read the 'new' page and
see cool stuff. Some of it wouldn't get to the top/front page. Most of it,
even the stuff in 'new', was usually pretty good. As it is now, only the
top/front page of HN is good to read. Going through 'new' is like becoming a
human crap filter.

Please don't just submit any crap you feel like because maybe it will get
voted to the front. Only submit good stuff.

"HN is not something that you just dump something on. It's not a big truck.
It's a series of people complaining."

