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03-15-2010, 01:57 PM   #1
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Modern LED Stage Lighting & photography problems

A lot of venues are now using LED stage lighting and the effects and color range/gamut can be very impressive.

LED PARs
(kind of a misnomer - as PAR stands for parabolic aluminum reflector - there is no reflector used in LED lighting - it's just the housing imitates traditional PARs)


and less traditional shape -


Basically LED lighting mix Red, Green and Blue LEDs to get almost any color.

White for example is RGB in equal proportions.

There is a tendency to use blue and red LEDs to get magenta - which is attractive and quite flattering - so it is more and more popular.

Although the combination is magenta to our eyes - it is in reality made up with red and blue light -
this makes a difference to photography/cameras -
as the resultant light is actually red and blue and pretty narrow wavelength/spectrum band too.

This makes any white balance very difficult in-camera or post-processing since the light really only has red and blue components (and little or no green) - shooting RAW unfortunately does not help since the original image lacks green in the spectrum - so it is almost impossible to get a white balance to get correct flesh/skin tones.

Not only that red and blue and very difficult for JPG to store/display -
so one loses details in those magenta areas -
so what may have looked sharp in the image when saved to JPG could end up looking soft or even seemingly out of focus.

here's an illustration:

this is with my normal post-processing/sharpening and JPG quality level -
it looks soft and even out of focus.

This is what I did to mitigate the loss of definition due to JPG compression -

this is over-sharpened by two steps over my normal - in the editor it looks very over sharpened - but when saved it is only slightly over-sharpened - one step over normal would still look soft....

I could preserve more definition by saving at a lower JPG compression too - but the file sizes are larger:

this is at 100% best JPG quality in my usual editor -
it is not that much improvement - and the file is now 124Kb vs. the 23Kb of the normally saved or 34Kb of the over-sharpened (which looks better albeit slightly over-sharp)


this is processed in PS Elements 7.0 -
where I did everything I know how to preserve the details -
resize bicubic sharpen, and enhance sharp eliminating lens blur - then saved at level 10 Max quality JPG resulting in a file that's 106Kb -
this actually looks pretty good.

I have found PS Elements 7.0 seems to do slightly better in its JPG compression is preserving details in red - but it is not that much better if one looks at the higher compression JPGs -

this is the same PSE 7.0 processed pic saved at level 4 quality and file size 24Kb roughly the same size as the first image posted. It is slightly better but still looks unacceptably soft.

There is also a double whammy sometimes with some sites like Picasaweb and some forums where lower compression larger filed JPGs are actually further compressed by the site resulting in softer looking images.

So even if one saves to a lower compression/larger file the site may re-compress the displayed image to show it soft.

That's why I ended up doing the over-sharpening of my images and saving to a higher compression JPG for a smaller file -
so that hopefully sites will not further compress my images.


Last edited by UnknownVT; 03-16-2010 at 09:48 AM.
03-15-2010, 02:21 PM   #2
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But you would not expect at all, to get "correct flesh" skin tones under strong coloured light - not even in the old days of tungsten(halogent lighting and gels! I mean, the colouring is the intended effect and why would you try to balance it out? I always simply set my camera to a fixed colour temperature when shooting stage events, which I set accordingly to the white lighting (or what is intended to be the white lighting) and then leave it at that. This way I can record the colour effects nicely.

Nevertheless I agree, that LED lights are not really nice to us photogs, as they only cover small parts of the spectrum, due to their non-linear emissions. Preserving skin tones is indeed not that easy, as you can see in my example shots.

Ben

CAVEAT: the JPG conversion has somewhat lost the skin colours, which I had recoveredů
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03-15-2010, 03:02 PM   #3
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QuoteOriginally posted by Ben_Edict Quote
But you would not expect at all, to get "correct flesh" skin tones under strong coloured light - not even in the old days of tungsten(halogent lighting and gels!
Thanks for the input.

In the old days of gels over halogen lighting there was still a reasonable amount of green in spectrum which allowed for better white balancing -
with LEDs there is almost a total lack of green in the spectrum when the green LEDs are not used, as in my shots.

I don't really try to get true skin/flesh tones under strong colored lighting I was talking more about the difficulty in getting any semblance of white balance control and merely used flesh/skin tones as an illustration -
but the generic advice appears to be to use RAW - as if that could -
RAW canNOT do much better either, when the lighting severely lacks green in the spectrum as in LED lighting.

There is actually a very good and succinct summary/explanation in post #8 in LED Stage lighting over at CPF.
03-15-2010, 03:12 PM   #4
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QuoteOriginally posted by UnknownVT Quote
Thanks for the input.

In the old days of gels over halogen lighting there was still a reasonable amount of green in spectrum which allowed for better white balancing -
with LEDs there is almost a total lack of green in the spectrum when the green LEDs are not used, as in my shots.

I don't really try to get true skin/flesh tones under strong colored lighting I was talking more about the difficulty in getting any semblance of white balance control and merely used flesh/skin tones as an illustration -
but the generic advice appears to be to use RAW - as if that could -
RAW canNOT do much better either, when the lighting severely lacks green in the spectrum as in LED lighting.

There is actually a very good and succinct summary/explanation in post #8 in LED Stage lighting over at CPF.
Tungsten and halogen light is continous lighting (temperature radiation), whereas LEDs are "only" emission radiators - even the so-called "white" LEDs will not emit a continous spectrum, but only several emission lines, which mix up and will be perceived by the eye as white light. The camera sensor is not that easily be fooled, as you rightly pointed out.

As colours do not exist on objects, but only their light absorbing or reflecting properties, the recoreded colours on the sensor will more or less massively shift with the light source. If the light source lacks parts of the spectrum, these colours cannot be reproduced. And you are fully correct, when stating that not even RAW would bring back colours that are not recorded.

Ben

03-15-2010, 03:29 PM   #5
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QuoteOriginally posted by Ben_Edict Quote
Tungsten and halogen light is continous lighting (temperature radiation), whereas LEDs are "only" emission radiators - even the so-called "white" LEDs will not emit a continous spectrum, but only several emission lines, which mix up and will be perceived by the eye as white light. The camera sensor is not that easily be fooled, as you rightly pointed out.

As colours do not exist on objects, but only their light absorbing or reflecting properties, the recoreded colours on the sensor will more or less massively shift with the light source. If the light source lacks parts of the spectrum, these colours cannot be reproduced. And you are fully correct, when stating that not even RAW would bring back colours that are not recorded.
Thanks for the confirmation and summary Ben.

Have you found any way of mitigating loss of detail with "magenta" (red and blue LED only) lighting?

I see you have similar problems in the first pic of the drummer you posted -
the loss of detail in the face almost looks like you mis-focused
(I'm pretty sure you did not)
as the drum kit + the second line on the T-shirt looked fine...
03-15-2010, 07:02 PM   #6
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Couple issues going on, probably. One, the bayer grid is 50% green, so right off the bat, you've halved your detail. Two, half the remaining light is red, which is at the opposite end of the spectrum of the other remaining half, so each of those will focus as far apart from each other as possible (CA). Three, you are getting clipping in whatever channel the light source is.

Shooting raw and pp may help, and editing in 16bit ... I'm not sure if this is in the direction you are looking for or not: it's a little bit muddy, but you can see that even with the tiny jpeg there is still a little bit there to work with ...

edit: actually the more I look at it, it's a lot bit muddy. Oh well.
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03-15-2010, 09:09 PM   #7
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QuoteOriginally posted by kxr4trids Quote
I'm not sure if this is in the direction you are looking for or not: it's a little bit muddy, but you can see that even with the tiny jpeg there is still a little bit there to work with ...
edit: actually the more I look at it, it's a lot bit muddy. Oh well.
Thanks for the try - unfortunately that's not the direction I was going -
I actually quite like the color balance as-is -
as I said, the magenta (made up with red and blue LEDs) is quite pleasing to the eye -
that's why it's getting more and more popular/prevalent.

That's the reason I posted - even though it looks good to the eye it plays havoc with photos -
for the reasons already posted here and over at CPF.
I already understood that - I was merely pointing out this difficulty in photos
and the crude way I have managed to mitigate some of this problem - by over-sharpening to compensate for the inevitable JPG loss in compression.

I'll reiterate about RAW - yes, it is superior - that is until one actually has to save it to JPG -
then one faces exactly the same loss of detail due to compression issues.
Saving in JPG is unavoidable if one actually wants to display the photo on the web.

Lower compression/larger file JPG is better -
BUT there are sites that compress overly large JPGs -
so we're back to square one.
03-16-2010, 03:34 AM   #8
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QuoteOriginally posted by UnknownVT Quote
Thanks for the confirmation and summary Ben.

Have you found any way of mitigating loss of detail with "magenta" (red and blue LED only) lighting?

I see you have similar problems in the first pic of the drummer you posted -
the loss of detail in the face almost looks like you mis-focused
(I'm pretty sure you did not)
as the drum kit + the second line on the T-shirt looked fine...
Part of the loss of detail in the drummer's face is sure due to motion blurr. These guys never sit still… Also, in my experience this strong magenta seems to exceed the colour gamut of the camera. I shoot RAWs exclusively and thus the working colour space in the camera is not important. My first edits in LR are always done in the ProPhoto colour space, which should offer the widest colour gamut. Indeed the RAWs or PSDs look slightly better, than these heavily compressed sRGB Jpgs. At least they do not have the clipping, evident in the Jpgs.

I could have rescued some of the magenta, if I had chosen a better approach while converting from RAW/PSD to JPG in PS CS4. For convenience I just used the Safe for Web option. That is fast, but overrides the possibilities for a better colour space conversion. If you use the "Convert to profile" and use black point compensation (I use the German version od PS, so my menue translations may be slightly different from the real names), the RAW/PSD colour are much better preserved - though ofcourse the latitude for adjustments shrinks, if you convert to sRGB.

Ben

03-16-2010, 03:50 AM   #9
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Wow, looks like you are shooting photos for an Andy Warhol painting.
03-16-2010, 04:03 AM   #10
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Focus Issues

The other issue I've found with these lights is the narrow spectrum, is playing havoc with autofocusing. I am inclined to believe that both the red and blue are far from what the focus sensor is calibrated for.

The other issue is that the significant CA in some lenses, especially fast, are causing two independent solutions to be produced, one for the red and one for the blue.

All in all I have to say that this type of lighting is not our friend.
03-16-2010, 04:08 AM   #11
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(Bring Your Own Green)
03-16-2010, 04:16 AM   #12
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QuoteOriginally posted by omega leader Quote
The other issue I've found with these lights is the narrow spectrum, is playing havoc with autofocusing. I am inclined to believe that both the red and blue are far from what the focus sensor is calibrated for.

The other issue is that the significant CA in some lenses, especially fast, are causing two independent solutions to be produced, one for the red and one for the blue.

All in all I have to say that this type of lighting is not our friend.
That might all be true. I think, the image of the drummer, where the white lettering is sharp, but the magenta lit parts are much OOF may indeed indicate a problem with chromaticity of the lens. Even an APO lens will have problems to focus different single emission lines properly onto a common focal plain.

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03-16-2010, 09:20 AM   #13
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QuoteOriginally posted by omega leader Quote
The other issue I've found with these lights is the narrow spectrum, is playing havoc with autofocusing. I am inclined to believe that both the red and blue are far from what the focus sensor is calibrated for.

The other issue is that the significant CA in some lenses, especially fast, are causing two independent solutions to be produced, one for the red and one for the blue.

All in all I have to say that this type of lighting is not our friend.
This is very true and thank you for that input - this was also brought up in the thread I have over at CPF.

However I don't think either focusing or CA were problems in the sample shots I posted
- esp this one:


Details:

over-sharpened by 2 steps (1 step = PSE 7.0 Adjust Sharpness 100%, 1 pixel, remove Lens Blur)
left is saved to quality 4 my usual size (32Kb) - right is to quality 8 much bigger file size (76Kb) to show over sharpening

This clearly shows that the main subject is very well in focus and has good definition/details -
loss of details in the other samples posted - of this exact same shot - was due to JPG compression -
What I did to mitigate the loss of definition in JPG compression - over-sharpened by two steps over my normal - in the editor it looks very over sharpened - but when saved it is only slightly over-sharpened.

This was shot with the humble 18-55mm (Mk 1) kit zoom lens.

Pentax K-x - ISO4000, f/4.5, 1/60, 45mm

Last edited by UnknownVT; 03-16-2010 at 09:55 AM.
03-16-2010, 10:27 AM   #14
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have you tried adding noise?
03-16-2010, 10:30 AM   #15
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Thanks for posting this. I've encountered this lighting only once so far, and luckily the lighting guy wasn't going too crazy with the different colors; my biggest problem was how *bright* the lights were given they were more behind the band than above. I've seen similar issues to what's described here in ordinary (halogen?) stage lighting with gels. I gather these have a somewhat broader specturm than LED's, but still, if you've got a magenta gel on a halogen light, you're not giving your sensor much color info to work with. Although actually I think blue or green gels are worse.
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