Ad
Ad
Ad
Pages: [1]   Bottom of Page
Print
Author Topic: Why does the green traffic light photograph more like white than green?  (Read 7670 times)
Isaac
Sr. Member
****
Offline Offline

Posts: 2672


« on: October 16, 2012, 11:41:18 AM »
ReplyReply

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.)
Logged
Eric Myrvaagnes
Sr. Member
****
Offline Offline

Posts: 7790



WWW
« Reply #1 on: October 16, 2012, 12:19:39 PM »
ReplyReply

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?
Logged

-Eric Myrvaagnes

http://myrvaagnes.com  Visit my website. New images each season.
Ellis Vener
Sr. Member
****
Offline Offline

Posts: 1731



WWW
« Reply #2 on: October 16, 2012, 08:46:17 PM »
ReplyReply

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
Logged

Ellis Vener
http://www.ellisvener.com
Creating photographs for advertising, corporate and industrial clients since 1984.
hugowolf
Sr. Member
****
Offline Offline

Posts: 598


« Reply #3 on: October 16, 2012, 09:01:21 PM »
ReplyReply

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
Logged
bjanes
Sr. Member
****
Offline Offline

Posts: 2756



« Reply #4 on: October 16, 2012, 10:59:16 PM »
ReplyReply

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
Logged
stamper
Sr. Member
****
Offline Offline

Posts: 2533


« Reply #5 on: October 17, 2012, 03:12:52 AM »
ReplyReply

Are they really green? Everybody assumes that grass is green but more often than not it is mostly yellow. In the UK police officers now wear luminous yellow bibs over their uniforms. Try photographing them in bright light and they definitely become white.
Logged

Isaac
Sr. Member
****
Offline Offline

Posts: 2672


« Reply #6 on: October 17, 2012, 11:02:51 AM »
ReplyReply

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.)
Logged
Isaac
Sr. Member
****
Offline Offline

Posts: 2672


« Reply #7 on: October 17, 2012, 11:07:18 AM »
ReplyReply

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

Please provide some evidence that helps me understand why you say that.
Logged
hugowolf
Sr. Member
****
Offline Offline

Posts: 598


« Reply #8 on: October 17, 2012, 11:48:30 AM »
ReplyReply

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
Logged
Isaac
Sr. Member
****
Offline Offline

Posts: 2672


« Reply #9 on: October 17, 2012, 11:52:58 AM »
ReplyReply

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 ;-)
Logged
MarkH2
Jr. Member
**
Offline Offline

Posts: 92


WWW
« Reply #10 on: October 17, 2012, 09:35:57 PM »
ReplyReply

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
Logged
Eric Myrvaagnes
Sr. Member
****
Offline Offline

Posts: 7790



WWW
« Reply #11 on: October 17, 2012, 10:32:30 PM »
ReplyReply

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

-Eric Myrvaagnes

http://myrvaagnes.com  Visit my website. New images each season.
AlexanderB
Newbie
*
Offline Offline

Posts: 25


« Reply #12 on: November 08, 2012, 09:03:44 AM »
ReplyReply

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.
Logged
niznai
Jr. Member
**
Offline Offline

Posts: 56


« Reply #13 on: November 20, 2012, 07:52:55 AM »
ReplyReply

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, 08:48:13 PM by niznai » Logged
orchidblooms
Full Member
***
Offline Offline

Posts: 160


« Reply #14 on: December 10, 2012, 12:17:08 AM »
ReplyReply

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...


Logged
Petrus
Sr. Member
****
Offline Offline

Posts: 486


« Reply #15 on: January 02, 2013, 12:08:21 PM »
ReplyReply

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.
Logged
Pages: [1]   Top of Page
Print
Jump to:  

Ad
Ad
Ad