A Photography forum. PhotoBanter.com

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » PhotoBanter.com forum » Digital Photography » Digital Photography
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Photographing Ultraluminous LED-lit Art Projects



 
 
Thread Tools Display Modes
  #1  
Old March 20th 08, 04:39 AM posted to rec.photo.digital
Pooua
external usenet poster
 
Posts: 32
Default 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?
  #2  
Old March 20th 08, 02:02 PM posted to rec.photo.digital
Don Stauffer in Minnesota
external usenet poster
 
Posts: 464
Default Photographing Ultraluminous LED-lit Art Projects

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.
  #3  
Old March 21st 08, 04:35 AM posted to rec.photo.digital
Pooua
external usenet poster
 
Posts: 32
Default Photographing Ultraluminous LED-lit Art Projects

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?
  #4  
Old March 21st 08, 10:37 AM posted to rec.photo.digital
Martin Brown
external usenet poster
 
Posts: 821
Default Photographing Ultraluminous LED-lit Art Projects

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

  #5  
Old March 21st 08, 07:47 PM posted to rec.photo.digital
Bob Williams
external usenet poster
 
Posts: 451
Default Photographing Ultraluminous LED-lit Art Projects

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
  #6  
Old March 21st 08, 08:04 PM posted to rec.photo.digital
Marco Tedaldi[_2_]
external usenet poster
 
Posts: 15
Default Photographing Ultraluminous LED-lit Art Projects

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
  #7  
Old March 22nd 08, 06:48 AM posted to rec.photo.digital
Pooua
external usenet poster
 
Posts: 32
Default Photographing Ultraluminous LED-lit Art Projects

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.
  #8  
Old March 22nd 08, 09:37 AM posted to rec.photo.digital
Martin Brown
external usenet poster
 
Posts: 821
Default Photographing Ultraluminous LED-lit Art Projects

In message
,
Pooua writes
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.


But the human eye perceives purple as blue with a red leakage. So you
can get a very convincing purple and magenta out of the RGB colour
space. The problem is more in the image capture device itself that to
optimise its performance on flesh tones where our eyes are very
sensitive to slightly off colour casts they have to lose the residual
errors somewhere and usually it is along the line of purples.

You can't fix it with Photoshop either because PS also uses an RGB
palette (e.g. Adobe RGB).
Bob Williams


The wavelength doesn't really matter only how it stimulates the eye
sensors. This could make for trouble if you do have something
illuminated with specific narrow wavelengths (monochromatic LEDs are
typically 50nm bandwidth on a nominal wavelength of somewhere between
650nm (red) and 350nm (violet) which makes them a much purer colour than
a typical gel filtered light source. At least with digital you can
experiment cheaply.

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)


They actually detect green, yellow and blue. Red is a creation of the
brain as the difference signal of yellow-green raw signal.

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.


Your best bet is to take a series of photos that span a range from
wildly underexposed to capture the true colours of each light source to
over exposed to capture the overall lighting effect. Finding a nice way
to combine them is a bit of a challenge, but provided nothing moves
between the shots it should be possible using some of the high dynamic
range tricks from combining multiple exposures. Good luck!

Regards,
--
Martin Brown

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

  #9  
Old March 22nd 08, 10:23 AM posted to rec.photo.digital
Chris Malcolm[_2_]
external usenet poster
 
Posts: 3,142
Default Photographing Ultraluminous LED-lit Art Projects

Bob Williams wrote:
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.


That's true physically speaking, but not in terms of how the human eye
sees colour, which is in terms of three colour filtered bands. Which
is why for us there are three primary colours, and why, for example,
we can't tell the difference between a pure spectral green and the
optical illusion of an appearance of green produced by mixing blue and
yellow. A goldfish with its much larger number of colour sensors would
probably not be fooled by mixing blue and yellow.

The problem with violet is that while it's theoretically possible to
mix up an undetectable different equivalnce to any colour using three
primary colours, in practice it's extremely difficult to find
chemicals which produce exactly the three colours required. Which is
why high quality colour printers usually use more than three. There
will be printers and monitors capable of reproducing any specific
violet, but you might have one of those, and they might be rather
expensive.

The same problem exists in the camera. Just as in the old days of
colour film different manufacturers produced colour films with
different virtues and vices in their not quite perfect capture of
colour, so too with modern digital sensors. They're not perfect, and
in some at least that imperfection is visible as defects in violets.

--
Chris Malcolm DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
[
http://www.dai.ed.ac.uk/homes/cam/]

  #10  
Old March 22nd 08, 03:36 PM posted to rec.photo.digital
[email protected]
external usenet poster
 
Posts: 222
Default Photographing Ultraluminous LED-lit Art Projects

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
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Free plans and projects to share. The Hurdy Gurdy Man Digital Photography 1 February 9th 05 01:43 AM
Free plans and projects to share. The Hurdy Gurdy Man 35mm Photo Equipment 1 February 9th 05 01:43 AM
Free plans and projects to share. Intrepid Digital Photography 4 February 9th 05 12:05 AM
Free plans and projects to share. Intrepid 35mm Photo Equipment 2 February 9th 05 12:05 AM
Free plans and projects to share. Randy Replogle 35mm Photo Equipment 1 February 8th 05 02:14 PM


All times are GMT +1. The time now is 12:37 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright 2004-2018 PhotoBanter.com.
The comments are property of their posters.