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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? |
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. |
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? |
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 |
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 |
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 |
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. |
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 |
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/] |
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 |
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