Sensor saturation with live theater lighting?

T

TheaterDad

Member
A friend and I have been shooting stage stuff for years and have never encountered such as disconnect between what our eyes were seeing and what our HMC150 LCD displays said was being recorded. The stage was often flooded with blue light, enough for a nice visual effect but it was the only color the camera saw. In my video editor I can reduce blue while maintaining luminance and I can't say the result is what our eyes were seeing since I can't remember, but the result is OK enough. I'm just puzzled by what the camera did. Can someone explain?
 
It sounds like your blue channel was overexposed. Unfortunatly loss of color fidelity due to overexposure is a common occurance especially with very saturated red, green or blue stage lighting. Our eyes are able to handle the wide range of tones a lot better than a camera sensor can. If a particular lighting scheme includes very saturated colors, it's best to underexpose the scene to the point where all color channels are within range. I recommend using a color calibrated monitor and using a camera that has wide DR. This is also something that should be discussed with the lighting dept ahead of time so that you know what to expect.

In some cases the lighting of a production is especially exteme (usually in less experienced projects) This should be discussed with the client ahead of time so that they understand that it's impossible to retain color fidelity in these cases and that it will result in overexposure in a given color channel.
 
I agree. Expose so that the highlights look good. This means that faces and things will look much too dark. In post, raise just the shadows and mids (exactly how to do this depends on your software). Some warn against raising the shadows because it introduces noise. But I'm fine with as much noise as 35mm film or so. It's the only way to get good results with a videocamera and high-contrast lighting situations.
 
Thanks to you both. Suspicions confirmed. It's surprising we've never seen this before. No need to fool with color until now.
 
TheaterDad said:
A friend and I have been shooting stage stuff for years and have never encountered such as disconnect between what our eyes were seeing and what our HMC150 LCD displays said was being recorded. The stage was often flooded with blue light, enough for a nice visual effect but it was the only color the camera saw.
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Probably not -- it recorded everything it could. If there's no balance between the blue and everything else, there can be so little of everything else that it falls off the end of what the sensor can do. Eight bits can handle daylight just fine, but this isn't anything at all like daylight. If for example your blue channel was maxed out at 256, and your red channel was so weak it was recording at 1 (or less), then it surely looks like the camera didn't see the red. It did, but it didn't have enough bits available to record it.

TheaterDad said:
In my video editor I can reduce blue while maintaining luminance and I can't say the result is what our eyes were seeing since I can't remember, but the result is OK enough. I'm just puzzled by what the camera did. Can someone explain?
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What the camera did, was record to the best of its ability a scene that was way outside its design specs. If you want to do this on a regular basis, you'll probably want a camera that has a better chance of actually doing it. Something that can give you 4:4:4 color subsampling with at least 12 bits/channel. And probably 12+ stops of dynamic range would help with the shadows. But even with this, if all you've got is blue light, you'll get a blue recording.

And remember that cameras aren't eyes. The human eye / brain combination way outperforms cameras because humans are very adaptive. Our auto-white balance (which is actually an auto-black balance, designed to keep colors constant as we hunt for food in the ever changing light in the forest) puts modern cameras to shame. And we get to expose each point we look at in the scene with a different exposure while the camera has to give the entire frame the same exposure. Cameras and eyes are so different it makes little sense to compare them.
 
We shot with tungsten. The show had regular stage lighting but a number of scenes were blue. A few scenes used white LED lights and they corrected pretty well by a simple white balance correction. The blue scenes were dark and blue.
 
Would something like a ninja blade recorder help in this situation, giving you 4:2:2 colorspace. Or not since it is still coming from an 8 bit camera sensor?

btw good to see another hmc150 user on here again. Makes me wonder how many of these workhorse cameras are still being used
 
All my work is in theatre - I'm a production manager, so lighting, sound, video, effects - all my problem. Here's a potted history of what has happened.

What has changed are the theatrical light sources. Tungsten with white at 2800K or so - Tungsten Halogen with 3000, or 3200K has been the mainstay for years. The biggest problem is the use of gel (for the video people) with light sources not being mega bright, most lighting was in subtle colours often warm cool and neutral - so a pink, a light blue and a lavender being popular. Then came rock and roll and the need for deeper blues, primary reds, vivid green and all kinds of yellow and gold. Luckily PAR lamps turned up with brighter sources, so losing more light through the more saturated colours became livable with. Blue was still a bit grim. Congo Blue 181, Lee filter's popular really dark blue has a sharp spike at one blue frequency - hence the colour temp of 6700K, but on average, transmits less than 1% of the light - so a deep blue, but bright stage was impossible without huge amounts of light sources - and the heat absorbed - the other 99% made for good central heating!

Skip forward to now, and it's rare to find theatres without LED lighting. The venue I run has stacks of it from my stock. I can now wash the stage for the first time in bright, deep blue light - or to be accurate, any colour light. Lighting designers, costume designers and dance teachers simply love it. They can now do their Wicked number in 100% vivid green too.

However - the video side of things has not kept pace at all. Most really popular and competent cameras fall over with saturated light. The result is the washed out and often out of focus blue, and a tendency for any of the mixes of red and blue to be pink - regardless of the range of pinks the eye sees.

I suspect that there are two problems - the first is that any form of auto exposure system fails. The exposure is simply read at the frequency that is virtually missing. In old fashioned gel coloured blues, for example - there is still plenty of green and blue in the colour. In LED colours, red, green and blue are totally without the others - so setting red, has no blue or green components at all. The cameras overexpose - some quite mildly, others much worse. Then the processing has been designed for evenly balanced lighting with just tints to blue or red - not whacking great monochromatic pictures that keep changing. AGC in some cameras kicks in and tries to produce something better, but usually making it worse. My JVC cameras deal with it reasonably well. Sony's seem less happy with the saturated colours, and Panasonic come somewhere between them in my experience.

Video people complain about the horrible lighting - very understandable, but some venues are now totally LED, for energy and green reasons, so there's no going back. Hotels fit it, and so do many shops - and it is expanding.

In my work, we now always make sure the client makes the call. Do we light for video, or do we light for the audience. Once that call is made, the lighting will be designed to look good for the chosen subject. This is why when a video crew, arriving just as the audience are arriving will get short shift to their request for none of that nasty blue light - or worse, asking for this change during the show. This results in the lighting people being described as 'unhelpful' 'spoiling the shoot' and even 'rubbish lighting man who had terrible lighting - clearing clueless' (This one aimed at me personally on one show).

For the shoots where video is the primary aim, the lighting guy will need you to provide him with a monitor, and he will set his lighting states in advance to what looks good to the camera, and then use it during the show to keep everything in line. Without a monitor, he can only guess what you can see. Because of my video work, I leave one camera in the follow spot box at my venue, wired to a permanent monitor in the lighting box - but most venues do not have this facility.

You also need to keep up to date with lighting - RGBW - that is red green, blue and white is now becoming RGBWA+UV - with an amber LED being added, plus a UV one that has an even lower frequency. It's still got visible light, unlike true UV which doesn't.

What is certain is that you will come across this more and more. It also impacts on stills photographers too.

Up until LED - the light spectrum was continuous just peaks and troughs which could be eq'd out. Now we have gaps. So on stage, you could have a big spike in the red, and a smaller one in the blue - the result to the eye being magenta, the result to the camera being a guess. My Sony cameras see a tiny bit of the red with full blue, and show pink. turning that red right up still gives pink. Very odd.

I suggest that if you have specific lighting needs, you must detail them ahead of the job. Programming LED lighting also takes much longer, so asking for last minute changes is much, much more difficult to do. If you ask the lighting person to take the blue down in every cue, that's not just one or two button presses - it means going to each cue, finding out which fixtures have blue in them and dealing them down one, by one. If there are more than half a dozen or so LED lights - that is a major job, AND cannot be done with the audience present - as it would involve all kinds of horrible stuff getting to something the camera can live with. If in my venue, they ask for a blue state, that can easily be 50 plus channels - dialling each one down, or making it more pink takes a fair time to do!
 
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Nicely said!

Camera manufacturers aren't aiming for this market however. They make sure their cameras will work fine with daylight and cinema lighting as these are their primary markets.

Making a camera work well in a theater with lighting as Paulears describes would be a nightmare for a manufacturer. How do you make an autofocus work when you have no idea what frequencies of light you'll have available? How do you autoexpose when only 1/3 of your sensors are registering anything at all? How do you auto whitebalance with a single primary color?

It's easy enough to see why cameras fail under such conditions. What are the camera manufacturers supposed to do about it? That's a much harder question.
 
I have also been shooting in theatres (mainly dance concerts) for nearly twenty years and have been shocked by the severity of LED lights on blue and red.

However we learned very quickly to always run our cameras on manual focus and iris, and only ever try to open the iris to match what the eye can see (not over expose).

Then I have a really good chance in post to get a reasonable picture. This is also much easier with the new Primary Colour Correction now in Edius 8, it has made it SO much easier to rescue a pure blue stage!

Cheers,

Vaughan
 
It is not necessarily the camera sensor that clips chroma in theatrical situations. Often it is the relatively small REC709 gamut range that clips in the recorded signal. I would think this is a situation where recording in a relatively desaturated log color space could pay off in post if you have the time and inclination to grade it.
 
Razz16mm said:
It is not necessarily the camera sensor that clips chroma in theatrical situations. Often it is the relatively small REC709 gamut range that clips in the recorded signal. I would think this is a situation where recording in a relatively desaturated log color space could pay off in post if you have the time and inclination to grade it.
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yes, 100% the case. An FS7 shooting slog 3 can do wonders as compared to a baked in color profile when it comes to very saturated colored LEDs.
 
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