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"Red Eye" effect of animals



 
 
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  #1  
Old March 3rd 05, 11:14 AM
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Default "Red Eye" effect of animals

I am writing an article about "red eye" effect of people and animals.
What I noticed is when you take a photo of the same animal, its eyes
can have different colors on different photos or even its left and
right eyes has different colors on the same photo. I think this depends
on the angle at which you take a photo, rather than on tapetal color.
Am I right? I never heard of it before, so it is just my assumption...

Please see the photos of the animals:
http://www.colorpilot.com/redeye_effect01.html
all 6 pictures of a dog show actually the same dog...

What do you think?

Natalia

  #2  
Old March 3rd 05, 11:24 AM
Martin Brown
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wrote:

I am writing an article about "red eye" effect of people and animals.
What I noticed is when you take a photo of the same animal, its eyes
can have different colors on different photos or even its left and
right eyes has different colors on the same photo. I think this depends
on the angle at which you take a photo, rather than on tapetal color.
Am I right? I never heard of it before, so it is just my assumption...

Please see the photos of the animals:
http://www.colorpilot.com/redeye_effect01.html
all 6 pictures of a dog show actually the same dog...

What do you think?


It depends on the animal. A lot of late evening or night time predators
have a special reflective layer at the back of their retina that give
the photoreceptors almost twice the sensitivity of a human eye.

Hence you don't see red eye from blood vessels so much as bluish eye
from the reflective layer. The exact colour is very angle dependent.

Regards,
Martin Brown
  #3  
Old March 3rd 05, 11:24 AM
Martin Brown
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wrote:

I am writing an article about "red eye" effect of people and animals.
What I noticed is when you take a photo of the same animal, its eyes
can have different colors on different photos or even its left and
right eyes has different colors on the same photo. I think this depends
on the angle at which you take a photo, rather than on tapetal color.
Am I right? I never heard of it before, so it is just my assumption...

Please see the photos of the animals:
http://www.colorpilot.com/redeye_effect01.html
all 6 pictures of a dog show actually the same dog...

What do you think?


It depends on the animal. A lot of late evening or night time predators
have a special reflective layer at the back of their retina that give
the photoreceptors almost twice the sensitivity of a human eye.

Hence you don't see red eye from blood vessels so much as bluish eye
from the reflective layer. The exact colour is very angle dependent.

Regards,
Martin Brown
  #4  
Old March 3rd 05, 12:45 PM
Ron Hunter
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wrote:
I am writing an article about "red eye" effect of people and animals.
What I noticed is when you take a photo of the same animal, its eyes
can have different colors on different photos or even its left and
right eyes has different colors on the same photo. I think this depends
on the angle at which you take a photo, rather than on tapetal color.
Am I right? I never heard of it before, so it is just my assumption...

Please see the photos of the animals:
http://www.colorpilot.com/redeye_effect01.html
all 6 pictures of a dog show actually the same dog...

What do you think?

Natalia

Dogs and cats seem to have a lot more rods than cones in their retinas,
and the angle from which the light reflects seems to vary the color,
even though the rods aren't color sensitive. Fixing this problem in
post-processing is much like doing the same with human eyes, except that
many programs look for the red tones, which are usually absent in animal
eyes (excpet other primates).


--
Ron Hunter
  #5  
Old March 3rd 05, 01:36 PM
Joseph Meehan
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wrote:
I am writing an article about "red eye" effect of people and animals.
What I noticed is when you take a photo of the same animal, its eyes
can have different colors on different photos or even its left and
right eyes has different colors on the same photo. I think this
depends on the angle at which you take a photo, rather than on
tapetal color. Am I right? I never heard of it before, so it is just
my assumption...

Please see the photos of the animals:
http://www.colorpilot.com/redeye_effect01.html
all 6 pictures of a dog show actually the same dog...

What do you think?

Natalia


To oversimplify this a little, what is happening is the light from your
flash is reflecting off the back of the eye. Since the eyes are seldom at
the same angle, you often get different reflections. Different animals (we
are animals after all) have differences in the construction of their eyes so
the results tend to vary. Cats and other night animals tend to have a
totally different kind of iris designed for night vision so they tend to
display more of the effect.

Moving the main light source away from the camera tends to reduce the
problem since the reflections is less likely to be reflected back at the
camera.

--
Joseph Meehan

26 + 6 = 1 It's Irish Math


  #6  
Old March 3rd 05, 03:48 PM
DHB
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On Thu, 03 Mar 2005 10:24:29 +0000, Martin Brown
wrote:

wrote:

I am writing an article about "red eye" effect of people and animals.
What I noticed is when you take a photo of the same animal, its eyes
can have different colors on different photos or even its left and
right eyes has different colors on the same photo. I think this depends
on the angle at which you take a photo, rather than on tapetal color.
Am I right? I never heard of it before, so it is just my assumption...

Please see the photos of the animals:
http://www.colorpilot.com/redeye_effect01.html
all 6 pictures of a dog show actually the same dog...

What do you think?


It depends on the animal. A lot of late evening or night time predators
have a special reflective layer at the back of their retina that give
the photoreceptors almost twice the sensitivity of a human eye.

Hence you don't see red eye from blood vessels so much as bluish eye
from the reflective layer. The exact colour is very angle dependent.

Regards,
Martin Brown


Martin Brown,
you wrote

"A lot of late evening or night time predators have a special reflective
layer at the back of their retina that give the photoreceptors almost
twice the sensitivity of a human eye."


Thus this may well be the next major evolution to come along &
advance digital camera sensors. Picture a CMOS or CCD or other type
of sensor with a similar reflective coating thus providing nearly
twice the light sensitivity per unit of time/area. This may not
happen for a while because the brain has to perform rather complex
processing of the reflected light. So even a tiny field mouse has
many times the processing power of the fastest digital camera image
processor.

Rather humbling when you look at how far Mother mature is
ahead of us, but then again Mother nature has been working at it a lot
longer than we have. LOL

If you think this process would not work, I invite you to
check out how a LED (Light Emitting Diode) works to produce narrow
band light. This process is reversible, I often use different color
LEDs as sensors to "detect" light. A "white" LED is actually the best
example of the principle working in reverse. Just thinking out loud
as an E. T. Electronic Technician, not Extra Terrestrial.

Come to think of it, some of my friends & colleagues are still
waiting for me to call home! LOL!

Respectfully, DHB

"To announce that there must be no criticism of the President,
or that we are to stand by the President, right or wrong,
is not only unpatriotic and servile, but is morally treasonable
to the American public."--Theodore Roosevelt, May 7, 1918
  #7  
Old March 3rd 05, 05:50 PM
Owamanga
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On Thu, 03 Mar 2005 14:48:43 GMT, DHB wrote:

On Thu, 03 Mar 2005 10:24:29 +0000, Martin Brown
wrote:

"A lot of late evening or night time predators have a special reflective
layer at the back of their retina that give the photoreceptors almost
twice the sensitivity of a human eye."


Thus this may well be the next major evolution to come along &
advance digital camera sensors. Picture a CMOS or CCD or other type
of sensor with a similar reflective coating thus providing nearly
twice the light sensitivity per unit of time/area. This may not
happen for a while because the brain has to perform rather complex
processing of the reflected light. So even a tiny field mouse has
many times the processing power of the fastest digital camera image
processor.

Rather humbling when you look at how far Mother mature is
ahead of us, but then again Mother nature has been working at it a lot
longer than we have. LOL

If you think this process would not work, I invite you to
check out how a LED (Light Emitting Diode) works to produce narrow
band light. This process is reversible, I often use different color
LEDs as sensors to "detect" light. A "white" LED is actually the best
example of the principle working in reverse.


So, if you can just bundle 6 million of these leds together in a flat
panel (approx) 9m by 6m, you've got yourself a camera. Now, for the
lens...

Kidding aside, I have a BSc in Digital Electronics and was wondering
how the LEDs are used as sensors - you seem to imply that a red LED
can detect red light - is this primarily because it has a red filter,
(ie a clear-case red LED can't do this?), and what's so special about
the white LEDs in this respect?

--
Owamanga!
  #8  
Old March 3rd 05, 05:53 PM
Dave Martindale
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writes:

"A lot of late evening or night time predators have a special reflective
layer at the back of their retina that give the photoreceptors almost
twice the sensitivity of a human eye."


Thus this may well be the next major evolution to come along &
advance digital camera sensors.


Nonsense. The retina is somewhat transparent; a fair bit of light
passes through it without being absorbed and affecting the light
receptors. So a reflective layer behind the retina gives the light a
second chance to be sensed. But a CCD looks nearly black because it
absorbs pretty much all the light reaching it. The losses there are are
mostly due to the electrode patterns on the front side blocking light
before it gets to the light-sensitive parts. Nothing gets through, so
there would be no point to putting a reflective layer behind it.

The reflective layer also reduces resolution somewhat, which is why
animals that aren't night predators don't use it.

Rather humbling when you look at how far Mother mature is
ahead of us, but then again Mother nature has been working at it a lot
longer than we have. LOL


But our technology sometimes has very different tradeoffs than "mother
nature's".

If you think this process would not work, I invite you to
check out how a LED (Light Emitting Diode) works to produce narrow
band light. This process is reversible, I often use different color
LEDs as sensors to "detect" light. A "white" LED is actually the best
example of the principle working in reverse. Just thinking out loud
as an E. T. Electronic Technician, not Extra Terrestrial.


Sorry, how is this relevant in any way to making a CCD more sensitive?

Dave
  #9  
Old March 3rd 05, 10:08 PM
DHB
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On Thu, 03 Mar 2005 16:50:59 GMT, Owamanga wrote:

So, if you can just bundle 6 million of these leds together in a flat
panel (approx) 9m by 6m, you've got yourself a camera. Now, for the
lens...

Kidding aside, I have a BSc in Digital Electronics and was wondering
how the LEDs are used as sensors - you seem to imply that a red LED
can detect red light - is this primarily because it has a red filter,
(ie a clear-case red LED can't do this?), and what's so special about
the white LEDs in this respect?


Owamanga,
well I'm an ET, retired at that, not an EE but I will
do my best to explain it mostly from memory. No it's not the lens
color that determines the LED's light output color, it's composition
does that.

1st it might be helpful to state that "all" PN junctions
(diodes) emit photons when forward biased & the effect is reversible.
This is why we have "photo diodes & photo transistors". LED are simply
build to maximize this effect & the are doped with specific impurities
or made from different materials to alter the wavelength from the
usual UV to something usually within the human visual spectrum.

Red LEDs depending on the frequency & efficiency may be GaAsP,
IR (actually should be called NIR Near InfaRed) use AiGaAs or AaAsSi.
The same individual that invented the blue LED also invented the 1st
practical white LED that we use today. One of the 1st attempts to
create a white LED used 3 LEDs in 1 housing which produce what the
human eye perceived as some white but it also could see the 3 primary
colors used, especially if you did not look directly at it.

How was this problem solved? Fire a blue LED onto a Yellow
phosphor & the human eye see's what it believes is white. Don't ask
me to explain this, it's outside of my field. Have you ever seen
those white LED night lights? I have a few & have taken digital
pictures with 1 in the background & my camera recorded it as a very
light blue light.

The reason I specified a white LED is because the phosphor
acts a bit like a reflective surface of a nocturnal critter's eye.

Sorry about this being a bit off topic but I only intended to
indicated that it may be possible for this same principle to be
adapted to a digital camera's sensor to increase it's sensitivity to
light. Also, I did state "or other type of sensor" because it may not
be compatible with either CMOS or CCD.

And using an LED as a photo diode is not very efficient but
it's extremely inexpensive & works just fine for many applications &
does not require a narrow band optical or electronic filter because
it's response varies from only about 30-150 nanometers. Also it's
peak sensitivity is the same as it's peak color output if used as an
LED to "emit" light rather than "detect" it.

Most motors also work as poor quality generators, even the
motors running in your PC that keep it cool will produce a small
voltage when wind blows through it & spins it. A poor man's high wind
detector!

Respectfully, DHB

"To announce that there must be no criticism of the President,
or that we are to stand by the President, right or wrong,
is not only unpatriotic and servile, but is morally treasonable
to the American public."--Theodore Roosevelt, May 7, 1918
  #10  
Old March 3rd 05, 10:20 PM
Larry
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In article , says...
wrote:
I am writing an article about "red eye" effect of people and animals.
What I noticed is when you take a photo of the same animal, its eyes
can have different colors on different photos or even its left and
right eyes has different colors on the same photo. I think this depends
on the angle at which you take a photo, rather than on tapetal color.
Am I right? I never heard of it before, so it is just my assumption...

Please see the photos of the animals:
http://www.colorpilot.com/redeye_effect01.html
all 6 pictures of a dog show actually the same dog...

What do you think?

Natalia

Dogs and cats seem to have a lot more rods than cones in their retinas,
and the angle from which the light reflects seems to vary the color,
even though the rods aren't color sensitive. Fixing this problem in
post-processing is much like doing the same with human eyes, except that
many programs look for the red tones, which are usually absent in animal
eyes (excpet other primates).




The only real fix for this is to move the flash OFF CAMERA, and not get the
red-eye to begin with.

I purchased a handle/bracket (mounts on the tripod mount of the camera) at
Ritz Camera for $14 (US) that has a shoe for the flash. If your camera has a
pc cable connector you can put a flash on the handle and move the center of
the flash as much as 10 inches from the camera lens.

This works MUCH better all around (for people and animals).

If your camera doesnt have a PC connector for the flash you can put the flash
on aa "autotrip" module (another $10 (US) at Ritz) then put a piece of foil
or plastic over the on camera flash to reflect the flash toward the off
camera flash instead of the subject.

All of this only works in MANUAL without pre-flash or red-eye reduction
turned on.


--
Larry Lynch
Mystic, Ct.
 




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