Depth perception and contrasting colours

I have long enjoyed stereo photography, in cross-eyed and parallel
free-view, anaglyph through coloured glasses and cross-polarised
projections.

I was interested to see the "stereo" effect (unintentional) which can be
seen on some webpages which use strongly contrasting colours.

Like so:
http://www.mendosus.com/photography/colour-stereo.html

Can everyone here see the apparent differences in depth of the coloured text
on that page?
Can anyone resolutely *not* see it?

Does it work with one eye closed?
(It doesn't for me.)

More interestingly, can anyone offer a simple, understandable explanation
for the effect?

Googling produces some joy, but not much. (Too tight to pay for research
papers.)

Anyone think there could be implications here for landscape photography? (Or
is the effect too gross/unsubtle?)

--
Jeff R.
(more than one dimension)

"Jeff R." wrote in message
...
I have long enjoyed stereo photography, in cross-eyed and parallel
free-view, anaglyph through coloured glasses and cross-polarised
projections.

I was interested to see the "stereo" effect (unintentional) which can be
seen on some webpages which use strongly contrasting colours.

Like so:
http://www.mendosus.com/photography/colour-stereo.html

Can everyone here see the apparent differences in depth of the coloured
text on that page?
Can anyone resolutely *not* see it?

I'd be very surprised if anyone genuinly couldn't see it as I understand it
to be the result of fundamental physics and physiology rather than an
optical trick as much 3d stuff uses. That said the website you've given
isn't a particularly good one to show it up, it's more obvious when the
contrasting colours are large and touching or one on top of the other, try
pink(magenta) on blue.


Does it work with one eye closed?
(It doesn't for me.)

It certainly should as the effect is within the eye rather than between eyes
IYSWIM.


More interestingly, can anyone offer a simple, understandable explanation
for the effect?

From (slightly hazy) memory it's caused by chromatic abberation, or
differential focus, or differential magnification, or differential colour
(pick a term, I've seen all of them used), of the colours by the simply lens
of your eye. Photoraphers see this sort of thing a lot in lenses,
particularly long ones.
Your eye/brain is not a simple camera and doesn't just record what it sees
like a camera but rather interprets it to glean information. It's
(incorrectly) interpreting the chromatic abberation and hence different
focal points for the colours as distance information.


Googling produces some joy, but not much. (Too tight to pay for research
papers.)

Anyone think there could be implications here for landscape photography?
(Or is the effect too gross/unsubtle?)


Well, it only really happens with fully saturated colours (if you think
about the explanation you;ll see why) which is why it's common with in
additive colour systems (things which emit light like monitors) and not
often seen in subtractive colour systems (paints, books and printed photos)
although there was a superb album cover in the late 1970's or early 1980's
which demonstrated it really well with a word written in pink on a blue
background - I wish I could remember what it was called.
So if you're in the habit of taking photos of fully saturated pink mountains
against saturated blue skies look out!

Cheers,
Calvin

On 2009-08-28 00:07:42 -0700, "Jeff R." said:

I have long enjoyed stereo photography, in cross-eyed and parallel
free-view, anaglyph through coloured glasses and cross-polarised
projections.

I was interested to see the "stereo" effect (unintentional) which can
be seen on some webpages which use strongly contrasting colours.

Like so:
http://www.mendosus.com/photography/colour-stereo.html

Can everyone here see the apparent differences in depth of the coloured
text on that page?
Can anyone resolutely *not* see it?

Does it work with one eye closed?
(It doesn't for me.)

More interestingly, can anyone offer a simple, understandable
explanation for the effect?

Googling produces some joy, but not much. (Too tight to pay for
research papers.)

Anyone think there could be implications here for landscape
photography? (Or is the effect too gross/unsubtle?)

Color contrast is one of many testing and correction methods used in optometry.
A part of the Humphriss Immediate Contrast Test, is to have two solid
black square targets, one on a green field and one on a red field. The
eyes are tested individually and then binocularly
Due to focus in front of the retina for the shorter wave length, higher
frequency green and behind for the longer WL, lower frequency red, one
target will appear sharper than the other until correcting lenses
balance the vision binocularly. Then the targets should be seen with
similar clarity.
This is one of the reasons the old 3D glasses were one green and one
red lens, they screwed with your binocular balance to create the
illusion of 3D.

--
Regards,

Savageduck

Jeff R. wrote:
I have long enjoyed stereo photography, in cross-eyed and parallel
free-view, anaglyph through coloured glasses and cross-polarised
projections.

I was interested to see the "stereo" effect (unintentional) which can be
seen on some webpages which use strongly contrasting colours.

Like so:
http://www.mendosus.com/photography/colour-stereo.html

Can everyone here see the apparent differences in depth of the coloured
text on that page?
Can anyone resolutely *not* see it?
Yeah I see it.

Does it work with one eye closed?
(It doesn't for me.)
Likewise, it disappears for me with one eye closed too.

More interestingly, can anyone offer a simple, understandable
explanation for the effect?
Others have suggested the different focal length for
different coloured light, but I don't think it would make
that much effect, plus if that was the cause it should still
be present with one eye closed. Also if that was the cause,
the stereo effect should increase as you get closer (as the
difference in focus increases), and disappear with distance.
Whereas I find the opposite, as I get closer the 3D effect
lessens, as I get further away it increases until I'm about
3ft from the monitor. I put it down to an effect caused by
the Bayer filter on the retina, and a slight bug in the
Brain's raw image convertor and 3D engine. ;-)



Googling produces some joy, but not much. (Too tight to pay for research
papers.)

Anyone think there could be implications here for landscape photography?
(Or is the effect too gross/unsubtle?)
I've observed similar effects with highly saturated slides
too - eg photos of flowers, green meadows & blue sky.
Curiously the effect seems to disappear when projected. When
I first saw the effect with slides, I thought the effect was
caused by the different colour layers, but then I noticed
the perception didn't reverse when the slide was turned
over. And thinking about it more it couldn't be, because on
a slide the primary colours are made by subtraction from
multiple layers.

--
Jeff R.
(more than one dimension)

Calvin Sambrook wrote:
"Jeff R." wrote in message
Like so:
http://www.mendosus.com/photography/colour-stereo.html

Can everyone here see the apparent differences in depth of the
coloured text on that page?
Can anyone resolutely *not* see it?

I'd be very surprised if anyone genuinely couldn't see it as I
understand it to be the result of fundamental physics and physiology
rather than an optical trick as much 3d stuff uses.

"Optical trick" is a bit harsh, I think. All the techniques I am aware of
serve simply to present a slightly different image to each eye - each image
offset by (ideally) the spacing of one's eyes.

Contrasting colours on a black background provide a very real stereo
illusion, but I can't for the life of me see how it could be presenting
different (offset) images to each eye.

... That said the
website you've given isn't a particularly good one to show it up,

Really?
Is the illusion obvious to you in the first few (red/blue) line groups?


it's more obvious when the contrasting colours are large and touching
or one on top of the other, try pink(magenta) on blue.

Not sure I follow what you mean by "large", but I'll give it a go. Stay
tuned for updates.



Does it work with one eye closed?
(It doesn't for me.)

It certainly should as the effect is within the eye rather than
between eyes IYSWIM.

Yes, I follow, but my experience is that the effect *almost completely*
disappears when I close one eye. I think I'm kidding myself, but I fancy
there is only a tiny, marginal effect when viewed monocular, but there is
certainly a huge, easy-to-see effect when viewed binocular.



More interestingly, can anyone offer a simple, understandable
explanation for the effect?

From (slightly hazy) memory it's caused by chromatic abberation, or
differential focus, or differential magnification, or differential
colour (pick a term, I've seen all of them used), of the colours by
the simply lens of your eye. Photoraphers see this sort of thing a
lot in lenses, particularly long ones.

Y-e-e-e-es... (trying to figure out how CA would cause a stereo
illusion...)

Do you mean:
The different colours achieve focus at different points (even though the
source is coplanar), so the brain interprets that difference as a difference
in depth?
That makes sense, though it seems contrary to the evidence.
Would I be aware (consciously) of the differential focus? (Would I be able
to sense my eyes trying to focus differently?)
Would/(should?) all the colours appear to be in sharp focus simultaneously?
(as they demonstrably are)
Would this effect work monocularly? (I say it doesn't)

Nice idea.
I'm sure it's (at least) the germ of the answer. (different wavelengths
being interpreted differently)

Your eye/brain is not a simple camera and doesn't just record what it
sees like a camera but rather interprets it to glean information. It's
(incorrectly) interpreting the chromatic abberation and hence
different focal points for the colours as distance information.

(sorry - I repeated what you said)

Googling produces some joy, but not much. (Too tight to pay for
research papers.)

Anyone think there could be implications here for landscape
photography? (Or is the effect too gross/unsubtle?)


Well, it only really happens with fully saturated colours (if you
think about the explanation you;ll see why)

One of the sources I looked at cited a Van Gogh landscape
http://astro1.panet.utoledo.edu/~lsa.../19_wheatS.jpg
in which the pastel-blue sky/clouds appear to stand out behind the
pastel-green fore and mid-ground.
(from http://astro1.panet.utoledo.edu/~lsa...r/19_depth.htm - good stuff)

I don't know if the effect there is down to colour and depth perception, or
Van Gogh's genius, but either way I do see it... and the colours are pastel,
not saturated.

....which is why it's common
with in additive colour systems (things which emit light like
monitors) and not often seen in subtractive colour systems (paints,
books and printed photos) although there was a superb album cover in
the late 1970's or early 1980's which demonstrated it really well
with a word written in pink on a blue background - I wish I could
remember what it was called.

Likewise I recall a story book from my youth that featured bright red and
blue text on a black background - I found the 3D effect disturbing, even as
a young'un. Had to run my fingers over the book to be sure it was actually
flat. (it was)


So if you're in the habit of taking photos of fully saturated pink
mountains against saturated blue skies look out!

Not too many of those round here, so no risk.


Cheers,
Calvin

Thanks for your input.

--
Jeff R.

Savageduck wrote:
Color contrast is one of many testing and correction methods used in
optometry. A part of the Humphriss Immediate Contrast Test, is to
have two solid black square targets, one on a green field and one on a red
field. The
eyes are tested individually and then binocularly
Due to focus in front of the retina for the shorter wave length,
higher frequency green and behind for the longer WL, lower frequency
red, one target will appear sharper than the other until correcting lenses
balance the vision binocularly. Then the targets should be seen with
similar clarity.
This is one of the reasons the old 3D glasses were one green and one
red lens, they screwed with your binocular balance to create the
illusion of 3D.

Well, I use blue and red, but not to quibble.

The purpose of the coloured glasses in anaglyph 3D is (surely) only to
present different images to each eye - to separate the left image and make
it visible to the left eye, and vice versa.

Whilst I freely acknowledge the differential focussing you explained, I
don't think that has any effect on anaglyphs, which are essentially
monochrome.

I've been wrong before, though.

--
Jeff R.

Doug Jewell wrote:
Others have suggested the different focal length for
different coloured light, but I don't think it would make
that much effect, plus if that was the cause it should still
be present with one eye closed. Also if that was the cause,
the stereo effect should increase as you get closer (as the
difference in focus increases), and disappear with distance.
Whereas I find the opposite, as I get closer the 3D effect
lessens, as I get further away it increases until I'm about
3ft from the monitor. I put it down to an effect caused by
the Bayer filter on the retina, and a slight bug in the
Brain's raw image convertor and 3D engine. ;-)

Don't forget our over-active built-in anti-aliasing filters...

The getting closer/further away effect is what got me started on all this.
I've just got a new set-top box on my telly, and it has a blue on/off LED.
When I'm sitting on the lounge, watching the box, (a large proportion of my
life) the LED appears to be buried deep within the bowels of the box. When
I look at it close-up, it appears to be flush with the front panel. More
trickery.

Of course, the conspiracy theorist in me says that the LED is mounted on
tracks, and it detects my position and retracts accordingly.

--
Jeff R.
(adjusting the tinfoil hat)

Jeff R. wrote:
Calvin Sambrook wrote:
it's more obvious when the contrasting colours are large and touching
or one on top of the other, try pink(magenta) on blue.

This what you meant?
http://www.mendosus.com/photography/colour-stereo.html
(updated with new image) http://www.mendosus.com/photography/six-colour.gif

--
Jeff R.

"Jeff R." wrote in message
...
I have long enjoyed stereo photography, in cross-eyed and parallel
free-view, anaglyph through coloured glasses and cross-polarised
projections.

I was interested to see the "stereo" effect (unintentional) which can be
seen on some webpages which use strongly contrasting colours.

Like so:
http://www.mendosus.com/photography/colour-stereo.html

Can everyone here see the apparent differences in depth of the coloured
text on that page?
Can anyone resolutely *not* see it?

Does it work with one eye closed?
(It doesn't for me.)

More interestingly, can anyone offer a simple, understandable explanation
for the effect?

Googling produces some joy, but not much. (Too tight to pay for research
papers.)

Anyone think there could be implications here for landscape photography?
(Or is the effect too gross/unsubtle?)

--
Jeff R.
(more than one dimension)




Interesting. It reminds me of a color display I saw back in the 1970's. It
worked by putting the three colors at different levels on the screen, and
accelerating the electron stream at three different energies, in order to
get it to penetrate the glass to the different levels necessary to get the
three different colors......Rather complex and expensive, but it
worked......

"Jeff R."


| Can everyone here see the apparent differences in depth of the coloured
text
| on that page?

yes

| Does it work with one eye closed?

yes

| More interestingly, can anyone offer a simple, understandable explanation
| for the effect?

differing points at which the various wavelengths focus (as put well by
others)