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Author Topic: Why does the green traffic light photograph more like white than green?  (Read 11048 times)

Isaac

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During a stroll yesterday evening, I took some snaps and noticed that I didn't seem able to make my Sony SLT-A35 record as-green-a-green-light as I saw, cast from the traffic lights onto the surroundings -- red and yellow, yes; green, not really.

I worked through the white balance options but without really bridging the difference between what I saw and what the camera recorded.

(These were old traffic lights, with a red / yellow / green filter glass over a similar light source.)
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Eric Myrvaagnes

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Re: Why does the green traffic light photograph more like white than green?
« Reply #1 on: October 16, 2012, 01:19:39 PM »

Hi Isaac,

Curiously, to me all "green" traffic lights look basically white. But then I'm "color-blind" (common red-green variety).

So maybe your camera sensor is color-blind, too?
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-Eric Myrvaagnes

http://myrvaagnes.com  Visit my photo website. New images each season. Also visit my new website: http://ericneedsakidney.org

Ellis Vener

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Re: Why does the green traffic light photograph more like white than green?
« Reply #2 on: October 16, 2012, 09:46:17 PM »

During a stroll yesterday evening, I took some snaps and noticed that I didn't seem able to make my Sony SLT-A35 record as-green-a-green-light as I saw, cast from the traffic lights onto the surroundings -- red and yellow, yes; green, not really.

I worked through the white balance options but without really bridging the difference between what I saw and what the camera recorded.

(These were old traffic lights, with a red / yellow / green filter glass over a similar light source.)
Simple reason: over exposure of the green light which obviously is a  light source
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Ellis Vener
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Creating photographs for advertising, corporate and industrial clients since 1984.

hugowolf

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Re: Why does the green traffic light photograph more like white than green?
« Reply #3 on: October 16, 2012, 10:01:21 PM »

Simple reason: over exposure of the green light which obviously is a  light source
Which given the green light is brighter than the other two, is easy to do. WIth the more recent LED traffic lights, the three colors tend to be more or less even illuminating, but the red and amber filter/lens are stronger than the green ones
Brian A
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bjanes

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Re: Why does the green traffic light photograph more like white than green?
« Reply #4 on: October 16, 2012, 11:59:16 PM »

Which given the green light is brighter than the other two, is easy to do. WIth the more recent LED traffic lights, the three colors tend to be more or less even illuminating, but the red and amber filter/lens are stronger than the green ones
Brian A

Even if the brightness of the lights were the same, the green channel would blow first. The color sensitivities measured by DXO for D50 show that the green channels are considerably more sensitive to green than red and blue. As the green channel blows, the color is pushed towards white. With more overexposure, all channels would be saturated and the color would be white.

Regards,

Bill
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Isaac

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Re: Why does the green traffic light photograph more like white than green?
« Reply #6 on: October 17, 2012, 12:02:51 PM »

Simple reason: over exposure of the green light which obviously is a light source

That is obvious now that you point it out :-)

(And it's testable.)
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Isaac

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Re: Why does the green traffic light photograph more like white than green?
« Reply #7 on: October 17, 2012, 12:07:18 PM »

Which given the green light is brighter than the other two...

Please provide some evidence that helps me understand why you say that.
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hugowolf

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Re: Why does the green traffic light photograph more like white than green?
« Reply #8 on: October 17, 2012, 12:48:30 PM »

Please provide some evidence that helps me understand why you say that.
Take a shot of each light using the same exposure settings and examine the luminosity of each color in an editor such as Photoshop. Of course this doesn't rule out that the increased brightness is due to the sensor being more sensitive to green, but really that doesn't matter, if it is brighter to the sensor then it is brighter in the image.
Brian A
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Isaac

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Re: Why does the green traffic light photograph more like white than green?
« Reply #9 on: October 17, 2012, 12:52:58 PM »

Of course this doesn't rule out that the increased brightness is due to the sensor being more sensitive to green, but really that doesn't matter, if it is brighter to the sensor then it is brighter in the image.

If you meant to say that the green traffic light is brighter than the red traffic light, then I think it matters ;-)
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MarkH2

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Re: Why does the green traffic light photograph more like white than green?
« Reply #10 on: October 17, 2012, 10:35:57 PM »

Hi Isaac,

Curiously, to me all "green" traffic lights look basically white. But then I'm "color-blind" (common red-green variety).

So maybe your camera sensor is color-blind, too?


** OFF TOPIC **

Eric,
I've often wondered what your icon pic was.  I visited your website.  Voila!  A pleasure.
Mark
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Eric Myrvaagnes

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Re: Why does the green traffic light photograph more like white than green?
« Reply #11 on: October 17, 2012, 11:32:30 PM »

Thank you, Mark. It's an example of my own special variety of "street" photography.
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-Eric Myrvaagnes

http://myrvaagnes.com  Visit my photo website. New images each season. Also visit my new website: http://ericneedsakidney.org

AlexanderB

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Re: Why does the green traffic light photograph more like white than green?
« Reply #12 on: November 08, 2012, 10:03:44 AM »

It's pretty hard to capture the color of light source due to the limited dynamic range of camera, especially digital one. In the night all neon lights, traffic lights start looking unnatural. Personally I hate how red becomes yellow.
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niznai

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Re: Why does the green traffic light photograph more like white than green?
« Reply #13 on: November 20, 2012, 08:52:55 AM »

I think it may be something to do with the fact that there's twice as many green sites on the sensor than each of the other two (or red and blue together have as many photosites as green alone).

That plus the fact that green radiation around 550nm is higher in energy than the red @ about 600. Blue is about 400nm though so should be higher than green so am not sure about this one. If the efficiency of blue photosites however is lower, this might explain it. No idea if it is true though.
« Last Edit: November 20, 2012, 09:48:13 PM by niznai »
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orchidblooms

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Re: Why does the green traffic light photograph more like white than green?
« Reply #14 on: December 10, 2012, 01:17:08 AM »

i have an image of a traffic light  - one capture i timed to catch the change...

the green is the brightest - could be it was exposed the longest --  this was 8 second exposure - did this on a whim... i was actually shooting in the opposite direction at the new twins stadium...  turned around as i was leaving - saw the building and light - waited - timed the light chang -- it is our public works building - my thought was to use it as our city workers not sure if they are on or off - service is often not so good in our depresssed area of mpls - (north side) this turned out to be the snap of that trip...


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Petrus

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Re: Why does the green traffic light photograph more like white than green?
« Reply #15 on: January 02, 2013, 01:08:21 PM »

With LED traffic lights the green also looks lighter (more luminous) to me than red and yellow. I do not know if this is on purpose, or if the green LEDs are more efficient than the red and yellow ones. Also the green looks less saturated, almost a mix of green, turquoise and white. Digital sensors also have problems with very narrow band colors, which possibly just hit the sensitivity peak of the sensor over saturating it. A color LED practically sends just one wavelength, something quite unnatural.
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