Photographing Ultraluminous LED-lit Art Projects

http://web.mit.edu/neltnerb/www/artwork/index.html features artwork
illuminated by super-bright LEDs, but the photos do not accurately
reflect the colors of the lighting. The artist says that his camera
has trouble picking up the purple lighting, instead showing it washed
out, apparently because it is outside the normal color space of the
imaging sensor. Does that sound likely? What might a photographer do
to take better photos of these tricky lighting situations?

On Mar 19, 11:39 pm, Pooua wrote:
http://web.mit.edu/neltnerb/www/artw...x.htmlfeatures artwork
illuminated by super-bright LEDs, but the photos do not accurately
reflect the colors of the lighting. The artist says that his camera
has trouble picking up the purple lighting, instead showing it washed
out, apparently because it is outside the normal color space of the
imaging sensor. Does that sound likely? What might a photographer do
to take better photos of these tricky lighting situations?

Here is yet another problem. We frequently do not perceive with our
eyes the true color of LED or laser light sources if we view them
directly. Some of the cones can saturate, really throwing off our
eyeball calibration.

On Mar 20, 9:02*am, Don Stauffer in Minnesota
wrote:
On Mar 19, 11:39 pm, Pooua wrote:

http://web.mit.edu/neltnerb/www/artw...eaturesartwork
illuminated by super-bright LEDs, but the photos do not accurately
reflect the colors of the lighting. The artist says that his camera
has trouble picking up the purple lighting, instead showing it washed
out, apparently because it is outside the normal color space of the
imaging sensor. Does that sound likely? What might a photographer do
to take better photos of these tricky lighting situations?

Here is yet another problem. *We frequently do not perceive with our
eyes the true color of LED or laser light sources if we view them
directly. *Some of the cones can saturate, really throwing off our
eyeball calibration.

I suppose I could adjust hue in Photoshop. I've just never been very
accurate with that thing.

Any other ideas?

On 2008-03-20 21:35:48 -0700, Pooua said:

On Mar 20, 9:02*am, Don Stauffer in Minnesota
wrote:
On Mar 19, 11:39 pm, Pooua wrote:

http://web.mit.edu/neltnerb/www/artw...eaturesartwork
illuminated by super-bright LEDs, but the photos do not accurately
reflect the colors of the lighting. The artist says that his camera
has trouble picking up the purple lighting, instead showing it washed
out, apparently because it is outside the normal color space of the
imaging sensor. Does that sound likely? What might a photographer do
to take better photos of these tricky lighting situations?

Here is yet another problem. *We frequently do not perceive with our
eyes the true color of LED or laser light sources if we view them
directly. *Some of the cones can saturate, really throwing off our
eyeball calibration.

I suppose I could adjust hue in Photoshop. I've just never been very
accurate with that thing.

Any other ideas?

You have to get it right when you take the picture. Photoshop cannot
put back what was never there.
--
Waddling Eagle
World Famous Flight Instructor

"C J Campbell" wrote in message
news:200803221855388930-christophercampbell@hotmailcom...

You have to get it right when you take the picture. Photoshop cannot put
back what was never there.


What? In terms of hue and intensity?
Wanna bet?

--
Jeff R.

In message
, Don
Stauffer in Minnesota writes
On Mar 19, 11:39 pm, Pooua wrote:
http://web.mit.edu/neltnerb/www/artw...x.htmlfeatures artwork
illuminated by super-bright LEDs, but the photos do not accurately
reflect the colors of the lighting. The artist says that his camera
has trouble picking up the purple lighting, instead showing it washed
out, apparently because it is outside the normal color space of the
imaging sensor. Does that sound likely? What might a photographer do
to take better photos of these tricky lighting situations?

Here is yet another problem. We frequently do not perceive with our
eyes the true color of LED or laser light sources if we view them
directly. Some of the cones can saturate, really throwing off our
eyeball calibration.

Bayer mask cameras go haywire even more spectacularly with pure
monochromatic light. My old Kodak Dc-120 completely freaked out when
used to image an H-alpha narrow bandpass image of a prominence on the
sun. Even though it was a sub Angstrom passband red filter the image was
bright enough to saturate the red channel and put enough signal into the
green and blue through filter leakage in the cameras filters to give
bizarre results. I think it metered mainly on the green channel.

Digicams need to be deliberately underexposed on coloured lights or LEDs
to capture the colours otherwise they will wash out or worse turn some
other colour.

BTW If you think digicam rendition of the purple magenta line is bad you
should see some of the films. Certain flowers with strong purple flowers
present considerable difficulties in photographing accurately on film.

Regards,
--
Martin Brown

--
Posted via a free Usenet account from http://www.teranews.com

Pooua wrote:
http://web.mit.edu/neltnerb/www/artwork/index.html features artwork
illuminated by super-bright LEDs, but the photos do not accurately
reflect the colors of the lighting. The artist says that his camera
has trouble picking up the purple lighting, instead showing it washed
out, apparently because it is outside the normal color space of the
imaging sensor. Does that sound likely? What might a photographer do
to take better photos of these tricky lighting situations?


I think the reason is, that NO combination of RGB used in sensors can
produce violet (purple?) light. The visible color spectrum is ROYGBV.
All colors between R and B can be generated by mixing appropriate
amounts of R, G, and B. But Violet is a shorter wavelength than any of
the frequencies captured by an RGB sensor. So no combination of longer
wave lengths can produce a shorter wavelength.
You can't fix it with Photoshop either because PS also uses an RGB
palette (e.g. Adobe RGB).
Bob Williams

Bob Williams wrote:

I think the reason is, that NO combination of RGB used in sensors can
produce violet (purple?) light. The visible color spectrum is ROYGBV.
All colors between R and B can be generated by mixing appropriate
amounts of R, G, and B. But Violet is a shorter wavelength than any of
the frequencies captured by an RGB sensor. So no combination of longer
wave lengths can produce a shorter wavelength.
You can't fix it with Photoshop either because PS also uses an RGB
palette (e.g. Adobe RGB).

Wow... thank you for telling me this NOW... just today I was in the
botanic garden and had some really beautiful violet flowers which seemed
to be just blue on the camera display.
http://www.flickr.com/photos/kruemi/2349815089/
I've added some more red on my computer at home, but it's not really
near the color that they had actually.
Now that you explain it, its the reason, why it did not work.

Thank you

Marco

--
Dimage A2, Agfa isolette
http://flickr.com/photos/kruemi
http://profile.imageshack.us/user/kruemi/images

On Mar 21, 2:47 pm, Bob Williams wrote:
Pooua wrote:
http://web.mit.edu/neltnerb/www/artw...x.htmlfeatures artwork
illuminated by super-bright LEDs, but the photos do not accurately
reflect the colors of the lighting. The artist says that his camera
has trouble picking up the purple lighting, instead showing it washed
out, apparently because it is outside the normal color space of the
imaging sensor. Does that sound likely? What might a photographer do
to take better photos of these tricky lighting situations?

I think the reason is, that NO combination of RGB used in sensors can
produce violet (purple?) light. The visible color spectrum is ROYGBV.
All colors between R and B can be generated by mixing appropriate
amounts of R, G, and B. But Violet is a shorter wavelength than any of
the frequencies captured by an RGB sensor. So no combination of longer
wave lengths can produce a shorter wavelength.
You can't fix it with Photoshop either because PS also uses an RGB
palette (e.g. Adobe RGB).
Bob Williams

I don't know if that explains the problem.

1) Purple is actually a combination of red and blue.
2) The cones of our eyes only detect red, green and blue (some
extremely rare women can see a 4th color)

I just found a website that states that humans detect violet by
comparing the ratio of blue light to red light. According to the
article, humans could just as well use the ratio of blue light to
green light, but the human spectral response to green and red light in
the blue portion of the spectrum is about the same, so it does not
make a difference which system humans use.

Digital cameras, OTOH, are more likely to sense violet by the ratio of
blue to green light. So, the response is not the same. That's my take
on what the article is saying, anyway.

http://gene.bio.jhu.edu/violet/violet.html

It would seem from this that it would be possible to switch the green
and red channel to find the violet. Maybe. Possibly. But, what happens
to everything else in the photo?

Anyway, I am thinking that by beating the scene into submission
through the clever use of RAW mode, bracketing and maybe HDR, I ought
to be able to help this artist. Too bad that he is in Boston, while I
am in Dallas.

Pooua wrote:
On Mar 21, 2:47 pm, Bob Williams wrote:
Pooua wrote:
http://web.mit.edu/neltnerb/www/artw...x.htmlfeatures artwork
illuminated by super-bright LEDs, but the photos do not accurately
reflect the colors of the lighting. The artist says that his camera
has trouble picking up the purple lighting, instead showing it washed
out, apparently because it is outside the normal color space of the
imaging sensor. Does that sound likely? What might a photographer do
to take better photos of these tricky lighting situations?
I think the reason is, that NO combination of RGB used in sensors can
produce violet (purple?) light. The visible color spectrum is ROYGBV.
All colors between R and B can be generated by mixing appropriate
amounts of R, G, and B. But Violet is a shorter wavelength than any of
the frequencies captured by an RGB sensor. So no combination of longer
wave lengths can produce a shorter wavelength.
You can't fix it with Photoshop either because PS also uses an RGB
palette (e.g. Adobe RGB).
Bob Williams

I don't know if that explains the problem.

1) Purple is actually a combination of red and blue.
2) The cones of our eyes only detect red, green and blue (some
extremely rare women can see a 4th color)


Purple is a combination of red and blue, and cameras get that just fine.

But violet can be a combination of red and blue, or its very own
spectral self, from 410 nm down into the near ultraviolet at about 360 nm,
if you are young or have had cataract surgery.

I tested my Canon 30D with the 100 mm f/2.8 macro lens
with monochromatic (2nm wide) light. And what color
is violet?

Well, it is not violet, not blue, in fact it is BLACK, dead BLACK.

At 420 nm the camera is rather weak in response, and produces blue.
At 410 nm and below it is dead as a doornail.

I don't have any other lens with me, so I don't know whether it is
the lens or sensor.

I do add that Photoshop is perfectly capable of turning any color
you wish into the color that 410 or 400 or even 390 nm light looks like,
which is violet. The color that shows on a video screen is not near
as saturated, of course, but it is the correct color. Prints are even
worse saturation, but still you can get correct color.

Doug McDonald