neon

[Kinz]

I was photographing some red neon signs tonight and all except one looks more orange than red. Anybody know why? This happened with two different cameras -- a D200 and D300. I changed settings during shooting, but looking at the EXIF info, there doesn't seem to be any drastic change in the settings. Thanks for any info or help.

 

[Josh66]

Was it on auto white balance?

That's the only thing I can think of.

 

[CraniumDesigns]

yeah, mess with the white balance and see what happens. if that doesnt work, try changing it in a graphic editor like photoshop.

 

[EhJsNe]

The camera can pick up lights in different colors than what our eyes see. If you take a picture in flourescent light, the shot will come out green, even tho we see it as regular light.
It might just be that. All you can do is play with the settings, white balance, and if all else fails, just change it in Photoshop to whatever colour floats yer boat.

 

[Dwig]

The camera can pick up lights in different colors than what our eyes see. ...

This is exactly whats happening. The spectral sensitivity curve of the three sets of photosites (Red filtered, Green filtered, and Blue filtered) on any one digital sensor do not precisely match the spectral sensitivity curves of the three sets of cones in our eyes (cones are the biological equivalent of the digital sensor's photosites although there is an additional set in the eye call rods that serve as low light B&W sensors, something lacking in common digital sensor systems). The result is that some objects that reflect or emit very narrow color bands can reproduce differently on different sensor systems (CCD, CMOS, human eye, ...).

The two sections of "red" neon are emitting slightly different spectra. You eye can't easily distinguish, if it can distinguish at all, but apparently you camera's sensor sees a significant difference. Global color adjustments (white balance, color balancing, ...) will not cure the problem. You will need to locally color balance the one aberrant neon tube.

 

[Flash Harry]

Almost, we can distinguish but our brain compensates for colour shifts, this is why photographers during training waste lots of paper when hand printing colour neg, view the print, 3 seconds max, for colour castes, any longer and the brain does the math and it all looks ok, but yes, its a colour balance issue which can be corrected with filters, PS or tweaking settings in camera on a digital. H

 

[Kinz]

Ok, I went out last night and took pictures of the sign again, with different settings and adjustments. When I use flash, the sign is red -- even though it's the camera's flash, which I'm sure doesn't go as far as the sign is. I checked some other photos I took recently of a motel sign with red neon, and the red is red, although the one in question isn't. I checked the EXIF through Opanda and the settings, distances, etc. are very similar, so I'm thinking that the neon sign has some sort of different light being emitted, even though to the naked eye, they are both red. I can send the photographs and EXIF if anyone is interested, or might be able to tell something with this info. There is another sign I took years ago with a D70, and the red neon is red, so I'll see what it does with the D300 (just to be able to compare the two). I have some old photos taken with film, and all those are fine. I'm thinking I might get another film camera to do neon (maybe). This is just strange, and I'm like a dog with a bone sometimes. Thanks for the help.

 

[Josh66]

You never answered my quesion about auto white balance. I suspect that you are using it and that's why you're getting different results. Switch to another WB setting (I use daylight most of the time). Auto moves around, the others don't.

The neon lights probably made it pretty hard for auto WB to figure out what the right setting was.

I have some old photos taken with film, and all those are fine. I'm thinking I might get another film camera to do neon (maybe). This is just strange, and I'm like a dog with a bone sometimes. Thanks for the help.

^^^
The white balance wasn't changing slightly for each shot you took.

 

[EhJsNe]

The answer to all your questions is magic.

 

[Kinz]

Sorry TPF; I changed the white balance last night. Some I can see differences in some, but most I can't...at least in the color. I think I'm going to have to make a real study of this, and be more organized with documenting it. I think I might see a pattern, but I have to be more diligent with the process. I need to change the ISO too, and see if that changes anything. When it stops raining, I'll go back and check it again.

 

[Garbz]

Dwig may be close to the mark but I have another theory, especially as to why this drifts orange.

My guess (and I say guess because I haven't seen the image itself) is that you are clipping the highlights. No not the total highlights but the highlights for one channel only. Basically if you dramatically underexpose the photo the neon signs being red and self illuminating may already have a value of 255 (clipped). Now as you turn the exposure up the other channels have no where else to go. As (if) the green comes up first, the picture goes more orange.

Now a wider colour space would fix this but it would revert itself in that you need to be able to view the wider colour space which short of very professional level printing is somewhat hard. The other solution is "highlight recovery", which was designed to address exactly this problem. Highlight recovery attempts to compensate for the fact that colours dramatically drift as one channel saturates and the other increase in brightness, so shooting RAW and playing with the recovery tool may be your solution too. Beyond that, HDR, under exposing, exposure blending, or all other manner of techniques to bring the bright red lightsource under control.

 

[Kinz]

I checked some of the photos and actually, the neon tube is yellow, but the light on the background of the sign is what shows up red. I can get the "red" effect using flash, but when shot without the flash is when they look yellow. There is one though, that looks red. It was shot at 1/2 sec at f13. There is another one, a few after that one shot at 1/3 sec at f13 where the tubes look yellow. Maybe I'll look at this scenerio and see what happens. So maybe Garbz and Dwig might have it right. I'll check it and see. Thanks for everybody's knowledge and input. I'll try to get back down there tonight and test these theories.

 

[gsgary]

Try setting the WB to 2000K or under

 

[Dwig]

... My guess (and I say guess because I haven't seen the image itself) is that you are clipping the highlights. ...

Clipping can very likely be part of the issue. Particularily clippin in only one channel, red in this case.

The color shift seen between with and without flash can be attributed to three possible causes:

1. the flash exposures are such that less clipping occurs.
2. the flash exposures force a different WB altering the color rendition reducing the percieved differnce.
3. the flash exposures illuminate the neon tube from the outside mixing its natural color with the color it emits.

Neon tubes don't usually get their color from a dye or tint on or in the glass. Their color is controled by the gas mixture (neon and argon are the most common) and sometimes a phosphorescent coating on the inside of the tube. Also, mercury is sometimes introduced into the tube. Some red neon tubes look white when turned off. Illuminating these, when on, with a flash will mix the white component from the flash exposure with the tube's own red. Other red neon tubes are perfectly clear. You'll also find some cheap imported signs made with all white tubes that have been painted with translucent paints to give them colors. These aren't as bright, but work fine for the classic beer signs on the wall of a dark bar.

 

[andrew99]

I think over-exposure could be a problem... What Dwig said about clipping is true, the more over-exposed something is, the closer to white it looks. I'm not sure if you posted samples since my work is blocking a lot of image sites, but if you reduce your exposure by a stop or two, I bet the neon will look a lot more colourful.