# Red vs orange



## JEL (Nov 14, 2015)

Red vs orange.

Will stronger color-filters on a digital camera make any difference when shooting bright colors, or will color-accuracy still be off?

Here's an example-image showing the in-accuracy of red turning orange:






Is it avoidable without under-exposing your images into near-total darkness?

Is it a by-product of trying to make cameras super-sensitive and low-light capable?

The funny thing, which is not really funny, is that on film these color-shifts does not seem to happen as easily. Is that because film is basically stronger in its color-filtration, or is it the bayer-sensor of digital that plays some part here, or what is going on?

Here's a film-image similar to the image above, where the much better (in my opinion) colors can be seen:





I see these color-shifts on all digitals I've used and really want to know of a camera that doesn't have this 'flaw'.

Bright red lights turn orange.

Bright green lights turn cyan/teal (sometimes orange or yellow)

Bright blue light turns cyan (occasionally magenta)

Bayer-sensor issue or color-filter issue or something else related to digital?

And most importantly, short of going back to film; which digital cameras do not behave in this, to me, annoying way?

Thanks for any answers that can shed some (hopefully color-accurate) light on this


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## privatebydesign (Nov 14, 2015)

How are you shooting and processing?

Do you shoot RAW or rely on Canon jpegs? If RAW what are you using to process your files?

The truth is all you need to do to get accurate colours is make a custom camera profile, make a dual illuminante one and you can use it for most ligh sources. Making a profile takes about 15 seconds.

The accuracy, or not, you have at the moment is because you are relying on various software guesses as to what you want, tell it what you want and voila, the colours are good.

P.S. None of the cameras are flawed, your technique is.


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## dcm (Nov 14, 2015)

Shooting RAW or JPG? How are you setting white balance? Auto?


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## JEL (Nov 14, 2015)

I shoot raw and the only way I can keep bright red lights from going orange is by under-exposing dramatically.

I don't have this problem when shooting film (at exact same exposure settings)

I use Canon's DPP mostly, but also have Adobe lightroom and RawTherapee. I see the same problem in all.

I've done tests where I shot the same images on both digital and film, with the exact same exposure-settings, and the difference with bright lights is always there.
On film they stay red or go slightly pink (as in red with added white). On digital they go orange.

It does seem like it's exposure-related, but I can't tell if it's the color-filters on film that keep the green channel more efficiently out of the red channel (since obviously orange is red plus green), or if it's simply that digital calculates over-exposure by adding green channel to the RGB pixel-value (or if it's something else that happens)

In short; on digital I always get what seems to be spill-over from one RGB color-channel into another, thus creating false colors (bright reds become orange rather than staying red or going pink. On film it's much more difficult to get those false colors, for me at least.)


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## fish_shooter (Nov 14, 2015)

I do not think the problem is color accuracy so much as the red is overexposed. After all you are shooting into light sources (e.g., light bulbs) with red filters over them. If you are using Lightroom you could try to reduce the red luminance level which is located under HSL/Color/B&W in the develop module. Note that the green lights are also a bit overexposed. It is more difficult to overexpose color negative film.


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## jarrodeu (Nov 14, 2015)

What film are you using?

Jarrod


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## JEL (Nov 14, 2015)

fish_shooter said:


> I do not think the problem is color accuracy so much as the red is overexposed. After all you are shooting into light sources (e.g., light bulbs) with red filters over them. If you are using Lightroom you could try to reduce the red luminance level which is located under HSL/Color/B&W in the develop module. Note that the green lights are also a bit overexposed. It is more difficult to overexpose color negative film.



Do you think a steeper (more discriminate) color-filter would produce the same colors?

I'm thinking that the green channel pollutes the red channel because the color-filters are too weak (allowing too much of their neighboring color to be picked up in their own channel, which would perhaps also explain why the green goes cyan/teal, and the blue sometimes magenta and teal)

If I under-expose severely, the orange goes away and the color becomes pure. So there's definitely something happening when light rises over a certain intensity. My issue is just that with film it takes a lot to get these cross-colors (the orange where there should be only red), and I was just hoping somebody knew of a digital camera that behaved more like film in this regard.

As far as I understand, current digital is so close to the same dynamic range of film that over-exposure on its own should no longer really be an issue, but perhaps it isn't quite there yet 

Could it be the bayer-sensor that allows color-spillage? Or perhaps rather the sensor, that allows electric current to excite neighbor sensels such that the digital processor 'thinks' there should be green signal where there should really only be read (because all the sensels are at the same plane, rather than on individual planes as on film). It only happens on overloads (over-exposure), so perhaps this could be a possible explanation? (if a sensel is 'excited' by overload in electrical current from neighbor sensels, then I assume it might register this current as light even though it doesn't come through its color-filter. I'm guessing that perhaps such pollution might bypass the color-filters that otherwise filter out current from building on a sensel, and thus basically be color-indifferent. I'm just speculating here of course, in looking for a solution  )


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## JEL (Nov 14, 2015)

jarrodeu said:


> What film are you using?



I've run tests of Kodak, Fuji and Agfa.
All exhibit the same behavior.
They all seem quite a lot more resilient to these cross-channel color-changes than digital.


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## retroreflection (Nov 14, 2015)

The tail lights are overexposed. They are incandescent bulbs with red filters, so the light is mostly red, but a full spectrum is coming through.
Overexposure of a pure white source will have all channels saturate at the same time. Overexposure of a colored source will have the dominant channel saturate first. More exposure will add to the other channels, but the dominant channel is still saturated. The color will seem to shift as a result. Each pixel is like a bucket collecting rain. When the red bucket is full, more rain just overflows. The blue and green buckets still have room for more. The color is the ratio between the three buckets, but the ratio is wrong because you were spilling red for much of the exposure time.
Duplicating shots with the same settings is a waste. The ISO standard for film and digital imaging allows for substantial range, one manufacturer's 64 can be another's 100. Far more importantly, the response curves of film, CCD, Canon CMOS, Sony CMOS, and whatever else comes along will never be identical. Especially when they saturate.


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## sanj (Nov 14, 2015)

"Is it avoidable without under-exposing your images into near-total darkness?"

The lights are overexposed. The shot is not. You have to pick what part of the shot you want to reproduce 'properly exposed'.

Not wanting to start a debate but this is a good example of where DR comes into play. If you would have reduced exposure of this photo by 2 odd stops the lights would have been more manageable. Then you can open up blacks depending upon the sensor you used.


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## rs (Nov 14, 2015)

sanj said:


> "Is it avoidable without under-exposing your images into near-total darkness?"
> 
> The lights are overexposed. The shot is not. You have to pick what part of the shot you want to reproduce 'properly exposed'.
> 
> Not wanting to start a debate but this is a good example of where DR comes into play. If you would have reduced exposure of this photo by 2 odd stops the lights would have been more manageable. Then you can open up blacks depending upon the sensor you used.



+1

Underexpose, and use a custom curve to regain some highlight tone. Or if you're happy sticking with Canon, try enabling Highlight Tone Priority. It does that for you, adding around 1 stop of headroom in the highlights at the expense of shadow noise. Possibly not enough headroom for this scenario, but worth a shot.


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## mb66energy (Nov 14, 2015)

JEL said:


> [...]
> 
> [1] Do you think a steeper (more discriminate) color-filter would produce the same colors?
> 
> ...



I think your analysis is absolutely correct:
1: A very narrow red filter would give a r:255 value and leaves blue and red at zero. It would alter the color representation in the image.

2: A steeper filter for reds, greens and blues would help to give better "pure" primary colors.

Think about a filter array which separates the full spectrum into three intervals without any overlap: You will get a posterized image of red green and blue (EDIT __for light/colors of narrow spectral width__ -- not a useful representation of the scene!
You need the overlap to transform a pure orange of e.g. 600nm wavelength into a relative r-g-value - b should result in zero.
I read a lot about newer cameras with broader curves (=more overlap) for r, g and b to increase sensitivity. But by loosing color precision. I see better reds with my 5D classic which might have narrower (but necessarily still overlapping) filter curves compared to 600D or EOS M. Quantum efficiency is rated roughly half that of the newer cameras ...

While you need the overlap of the r, g and b spectra you can always run into the situation that the r channel is saturated while the overlapping part of the green channel is still acquiring photons/electrons and turning the resulting color into red.

About your examples: IMO they aren't comparable because the brake lights are much much much brighter than your film example with the "neons".

The only countermeasures are:
* much more really useable native DR (16EV +) of sensors (without downscaling) for each color channel
OR
* a sensor which has a spectrometer for each pixel and the pixel information is stored as (parametrized) optical spectrum. Resulting in ~100Bytes per pixel minimum ... 10MPixel (each pixel full color) = 1GByte raw data ... (good for card manufacturers etc.)

The latter idea is hypothetical but would result in extraordinary IQ because a spectral orange of 600nm wavelength is stored and not some mixture of red and green which maybe was produce by a mixed color (RGB LED).


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## scyrene (Nov 14, 2015)

Does it matter? Direct light sources are often overexposed in the centre, but does the image suffer for it? Most people wouldn't even notice.

You could underexpose. If this really bugs you, you'd be better off with one of those cameras you can pull the shadows up massively. Expose for the lights.

For static scenes, you could use multiple exposures (HDR).

If film is better at this, fine. No doubt film has some technical advantages over digital sensors. But this is such a tiny niche case it's academic.

I'm not sure what colour profiles could do, if those light sources are truly overexposed/fully saturated, the data cannot be recovered.

I guess you could get that B&W Leica and use colour filters


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## mb66energy (Nov 14, 2015)

I think it is allowed to speculate about CFA + sensor sensitivity and DR. If the brake light has 100 000 times
the energy density on the sensor compared to the light reflected by the cars which is 100 times brighter than the shadows you need 20 stops of usable dynamic range at least and fold it into the display which has 15 stops of DR in the optimum case: A well made OLED display.

Sometimes I am fascinated how good our eye-brain-system is and how bad just the best photographic systems - on the other hand: A photograph is the easiest way to communicate visual impressions to others!




privatebydesign said:


> Getting 'accurate' colours can be difficult, but to speculate about CFA sensitivity when you are not addressing the herd of elephants in the room is farcical.
> 
> You can get very close to 'accurate' colours, certainly much closer to 'accurate' than with film, with any digital camera ever made. BUT YOU HAVE TO PROFILE IT.
> 
> Trying to talk about 'accurate' colours while not addressing the most important and first step, camera profiles, is moronic.


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## fish_shooter (Nov 14, 2015)

JEL said:


> fish_shooter said:
> 
> 
> > I do not think the problem is color accuracy so much as the red is overexposed. After all you are shooting into light sources (e.g., light bulbs) with red filters over them. If you are using Lightroom you could try to reduce the red luminance level which is located under HSL/Color/B&W in the develop module. Note that the green lights are also a bit overexposed. It is more difficult to overexpose color negative film.
> ...



It was quite easy to overexpose transparency, i.e., slide film. One got a similar results, a shift towards white or the color of the film base.

On the internet people are discussing about how underexposure is fixed with the extended dynamic range of certain sensors. Overexposure, OTOH, is the kiss of death for images.


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## fish_shooter (Nov 14, 2015)

JEL said:


> jarrodeu said:
> 
> 
> > What film are you using?
> ...



IMHO, film type is more important for your problem than film brand. Did you shoot any transparency/slide film in your test?


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## privatebydesign (Nov 14, 2015)

mb66energy said:


> I think it is allowed to speculate about CFA + sensor sensitivity and DR. If the brake light has 100 000 times
> the energy density on the sensor compared to the light reflected by the cars which is 100 times brighter than the shadows you need 20 stops of usable dynamic range at least and fold it into the display which has 15 stops of DR in the optimum case: A well made OLED display.
> 
> Sometimes I am fascinated how good our eye-brain-system is and how bad just the best photographic systems - on the other hand: A photograph is the easiest way to communicate visual impressions to others!
> ...



Maybe, years ago. Nowadays most digital sensors are within a stop or so of the DR even the very best that negative films can achieve, the Exmor sensors and many video orientated sensors beat it, some by several stops. All digital sensors resoundingly beat the DR available from transparency film from their first release.

DR is a red herring when talking about colour like this. Basically, if you are going to blow highlights on digital you are going to do the same on film.


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## mb66energy (Nov 14, 2015)

privatebydesign said:


> mb66energy said:
> 
> 
> > I think it is allowed to speculate about CFA + sensor sensitivity and DR. If the brake light has 100 000 times
> ...



For transparency film I agree with you. But B/W negative film has -- what I read and remember from my dark darkroom experiences (20 years ago) -- roughly 18 stops of DR and I know that hollywood switched from positive film to negative film for movie production ... to benefit from the higher DR.

One remark about color calibration: For the blown out areas this wouldn't help but on the other hand it would help for the surrounding halos which arent blown out -- so your idea of color profiling as first step is right for most of the image! I have forgotten to differentiate ...


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## privatebydesign (Nov 14, 2015)

OK, which is 'accurate'?

One is as opened in LR so, by default, Adobe Standard, one is ACR4.4, one is custom profiled, one is Adobe Camera Portrait and one is Adobe Camera Landscape.

The point is they are all the exact same image file. If you shoot RAW you tell the rendering software what the colours should be, not the other way around, if you do that colours are 'accurate'.


EDIT: For those who struggle to see the differences, here are the five images layered as a gif. Just watch the red orange and yellow squares in the bottom right corner change, remember, these are all the same shot just using different camera profiles. The vast majority of the differences people talk about in various camera models 'colour reproduction' has nothing whatsoever to do with CFA filters, it is all down to software profiles.


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## mb66energy (Nov 14, 2015)

Simple shots of a cheapo RGB light source, a RGB LED from a light strip made with two cameras - EOS 5D classic (see file name) and EOS 600D under similar conditions and with the same settings / processing with DPP.

The blown out highlights from the LED crystals can be well observed while the (black) stripe shows virtually no structure.

The colors seem a little bit cleaner with the 5D classic but both cameras exhibit the violet halo around the blue LED ... I always wondered how a sensor would be which has IR and UV sensitive photosize to give better color information for deep reds and the violet color between blue and UV ...
But I am still impressed what can be done with just three color channels to fool our eyes and brains and I enjoy photography just with that old 5D!


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## privatebydesign (Nov 14, 2015)

mb66energy said:


> privatebydesign said:
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> 
> > mb66energy said:
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B&W film DR is pretty irrelevant in a thread about accurate colour reproduction  But if you look at the data sheet for Kodak TriX ( http://www.kodak.com/global/en/professional/support/techPubs/f4017/f4017.pdf ) you get a Log Exposure range of 3.3-3.6, or 11-12 stops.

As for negative film, again Eastman Kodak claim a Log Exposure range of 3.3-3.6, or 11-12 stops. And again is on the data sheet for the film http://www.kodak.com/global/en/professional/support/techPubs/e4050/e4050.pdf

Few modern digital cameras don't give 11 stops of DR, and many give over 12.

The film vs digital arguments died a long time ago, some of us just never heard the eulogy. Of course there are, and always will be, very good reason to shoot film instead of or with digital, but the technical differences are not particularly valid and as far as a colour reproduction argument go, are entirely false.

Think of it like this, how was the film image digitised? What profile was used, because there had to be one that somebody somewhere wrote and put in the scanning software.


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## privatebydesign (Nov 14, 2015)

mb66energy said:


> Simple shots of a cheapo RGB light source, a RGB LED from a light strip made with two cameras - EOS 5D classic (see file name) and EOS 600D under similar conditions and with the same settings / processing with DPP.



No they aren't. DPP has different profiles (different settings) for every single camera model, the differences are almost certainly just down to the different profiles for each camera, certainly if you made custom profiles for each you wouldn't see a noticeable difference.

All I am saying is the differences in profiles dwarf any differences inherent from different CFA's, and you can't hope to compare the differences in CFA's unless you truthfully normalise the RAW data. I think the only way you could do that effectively is to look at RAW files in something like DCRAW, but viewing RAW files without gamma corrections and heavy green bias is far from intuitive!

On a practical level I have done this 'getting everything the same' kind of thing, last year I shot a wedding with two other photographers, I used two 1DS MkIII's, another had a 5D MkIII and a 7D, and the third had two Nikons. After getting them to shoot color checkers a couple of times during the wedding I was able to normalise the output of all six cameras (and many lenses) to a level that, from a colour point of view, they were all the same.


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## JEL (Nov 14, 2015)

Ok, thank you for all your answers 

-No, I haven't shot slide-film, only negative-film.

-I get what you say about the need for overlap between the 3 channels, to produce colors in between of the primaries.



I highly prefer the look of the film-image (of the 2 images I posted)
Its reds are clearly saturated (maxed out), but they remain much more cleanly red anyway.
It's possible the picture-profile is where this difference should be addressed. I'll see what I can do with Canon's profile-editor (I dread using that though, but I'll try  )

I will also keep investigating for other solutions.

Maybe if digital processing would stop increasing the other channels when one is at its max-limit, then perhaps color-shifts could be avoided. Or if it blended the 2 other channels to the same value so the over-exposed channel would keep its color but just go towards white rather than a color-shift.
I don't know.

But if the lights went pink (red + white (if the G and B channel was equalized when the R channel was maxed out)) instead of orange I feel it would look a lot better, but of course that's a matter of taste 



Anyway, thanks again for your inputs and suggestions. 

Exposing for the lights is not a workable option, because in my experiments I had to lower exposure so much the image went black. The difference in brightness is just too large.

The digital image has some natural light still in it, while the film has a black night-sky. So technically I would assume the digital should have a better chance of keeping the car-lights within exposure-limits (since you need lower exposure when there's still natural light, than with a true night-scene)

Yet the film-image of the true night-scene keeps the reds red. It may be that the term 'color-accuracy' isn't really what I should have used here. What I meant is simply that I'd like the reds to stay red and not shift toward orange 


I was asking this question because with Christmas coming these types of colored bright lights (from decorations and so on) is something I would like to be able to capture correctly 
Past years my Christmas-images often end up with all the colors being mostly white blobs with colored halos, and I just would like to avoid a repeat of that this year.
In bright sun-light digital works just fine, but with night-time scenes I'm still having quite the fight with digital (and of course I'd like to use digital since it's much easier and quicker than film)


Thanks again everybody


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## privatebydesign (Nov 14, 2015)

JEL said:


> What I meant is simply that I'd like the reds to stay red and not shift toward orange



All you need to do is profile your camera, and accept that both digital and film have dynamic range limitations that are within a hairs breath of each other.


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## scyrene (Nov 15, 2015)

privatebydesign said:


> JEL said:
> 
> 
> > What I meant is simply that I'd like the reds to stay red and not shift toward orange
> ...



I am quite prepared to be proved wrong here, but if you fully saturate a colour channel, how does it matter what camera profile you use?


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## privatebydesign (Nov 15, 2015)

scyrene said:


> privatebydesign said:
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> 
> > JEL said:
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Once you exceed your capture mediums DR you are looking at white. Kodak specs agree that film has the same DR (or very close) as pretty much every digital camera available, blow the lights on one and you blew the highlights on the other.

The example images shown at the beginning of the thread don't have the same bulb intensity for the film and digital exposures so give the impression film doesn't blow the light bulbs, but in the same situation as digital, because they have very similar DR, it will.

So if we aren't talking about blown highlights, because we can't be because they have no colour, then a profile will make a difference.

Look at it like this, JEL says _"I'd like the reds to stay red and not shift toward orange"_ so we are not talking about blown highlights (white) but orange. To get orange the pixel is getting three channels of colour info, orange needs red, blue and green levels and only red could be at 255. Even if the red is at that 255 level if you lower the green and blue levels you get your red back, that is a textbook profile issue not a DR issue.


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## sanj (Nov 15, 2015)

privatebydesign said:


> JEL said:
> 
> 
> > What I meant is simply that I'd like the reds to stay red and not shift toward orange
> ...



+1 Hair's breath. I am an old timer who has shot on lots on film. I feel like saying digital has perhaps bettered film by now. (Ducks).


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## privatebydesign (Nov 15, 2015)

sanj said:


> privatebydesign said:
> 
> 
> > JEL said:
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Sanj,

You are a DP, in the video realm digital has comfortably bested every metric film has, iso, resolution, DR, colour, etc, there are still compelling reasons to shoot film if that is what the director wants, but it is an emotional decision now with a very nuanced and subtle difference/feel that few could distinguish.


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## sanj (Nov 15, 2015)

privatebydesign said:


> sanj said:
> 
> 
> > privatebydesign said:
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Yes Private. I know what you are saying. But this is my OPINION on it: The emotion decision is mostly because many people, rightfully so, rejected digital when it started stating that film has 'a special something'. It did. Then. Not now. The advantages of shooting digital far best the film days. I think now it is more of an 'emotional/intellectual' thing. Strictly my opinion. And, if anyone needed the 'grain', it is a simple filter while doing grading. It is very easy to recreate the film look: Crushed blacks, grain etc.


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## sanj (Nov 15, 2015)

scyrene said:


> privatebydesign said:
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> > JEL said:
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I would like to learn this too. I shoot RAW strictly. So does this 'profile' thing apply to me as well?


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## retroreflection (Nov 15, 2015)

A blown highlight does not immediately turn white. It goes from the true color to white along a color space slope defined by the ratio of the two remaining unsaturated channels. And, btw, I see white in the middle of at east one tail light. 
If a color gradient is visible across a light emitting device, it is overexposed. Is there any accurate color in there? That's a good question, but it's also a very deep rabbit hole.
If the OP can't expose for the lights, then a variable power flash to boost the rest of the scene this holiday may be in order.


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## rfdesigner (Nov 15, 2015)

This is the reason when I shoot at night I use a fixed 6000k colour balance, despite shooting RAW, then watch for blinkies in my highlights.

By doing the above the JPEG will see a blown red blue or green, if it adjusts the colour it can miss the blown single colour.

Additionally most surfaces reflect approx 10~20% total light (trees pavements walls etc.. I've done experiments for this myself), so with a diffuse or out of shot light source you want something close to the typical 18% of max exposure for typical illumination, white objects aren't blown, shadows have as much leeway left as possible.

If however you want to capture the true colour of say a setting sun, then you need ETTR exposure, which will always be a LOT darker, possibly 3 stops darker, than "evaluative".

The way I do it is to push my exposure to +2stops, then use the spot metering and meter on the brightest point, recompose and shoot... that gets me pretty close for most things other than really small bright sources.


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## JEL (Nov 15, 2015)

-Profiling on the to-do list.

-Using flash as fill may be the best option. I'll have to shoot some tests to see what settings and ratios will be optimal while still getting an image-tone that seems nice.

-Yes, I've used evaluative past years, but have already done a few tests with spot-metering. I can make that work fairly well on outside shots as long as it isn't completely dark/night (day and twilight is workable), but even then I often end up with shots so dark I can't really salvage it in post (I shoot the 5D3 currently and pushing shadows hasn't worked well for me. The sensor-noise patterns are very quickly showing themselves)

Why do you choose 6000K for night-shots? I've tended to use the preset 'daylight' setting, as my understanding is that that setting balances the red and blue channel equally (which I then use for histogram preview purposes during shooting)

Maybe I also need to re-think how I frame shots, to counter the short-comings of the camera (or at least to fit the camera-limits better to my limited skills  )

I'm not denying it could be user-error (camera profiling etc), but I do find that film handles bright colored spot-lights much better than digital. It just seems to separate the 3 color-channels better (which is why I thought it could be somehow related to stronger/steeper color-filters in film rather than those on the digital sensor)

Well, live and learn


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## Don Haines (Nov 15, 2015)

rs said:


> sanj said:
> 
> 
> > "Is it avoidable without under-exposing your images into near-total darkness?"
> ...


This is a situation where HDR photography is needed.

What you are doing is photographing light bulbs at night. You want the colour of the light bulbs to come through, but you also want the details in the rest of the picture to come through. If you expose for the light bulbs, the rest of the image is black... If you expose for the background, you run into the following problem: Coloured lights are usually done by placing a film or "tint" over the bulb. This tint is not monochrome. For example, the red bulbs might let 90 percent of the red light through, but they also let the other light through in lesser amounts. Your eye will still interpret this as red, but not so with the camera sensor. 

Lets say you properly expose for the highlights (red bulbs)... the red pixels are receiving 100 percent of the light they can capture and are on the edge of clipping the signal. Since that light is not pure monochrome and is not exactly matched to your bayer filter, both the green pixels and the blue pixels will also be receiving light, let's say at 5 percent green and 2 1/2 percent blue. If you look at the image the colour seems to match what you saw.

Now overexpose by three stops to get some of the detail in the shadows.... 3 stops means 8 times the light. The red pixels are now receiving 800 percent of the light they can capture, green at 40 percent, and blue at 20 percent. The sensor reports the levels at 100, 40, and 20 and we get a different colour.

The image below shows what you would see as a result, and yes, your red turns into orange.


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## pj1974 (Nov 16, 2015)

Don Haines said:


> rs said:
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> > sanj said:
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*Don*, that's a very good explanation of a semi-technical 'light matter', really useful for the average 'enthusiast' photographer to understand.

Well done for writing it, and sharing helpful information that way.

Best wishes... really appreciate your posts on CR.

Paul


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## ajfotofilmagem (Nov 16, 2015)

Don Haines said:


> rs said:
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> > sanj said:
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Thanks, Dom.
You got a few words, explain a phenomenon that requires a certain degree of abstraction to understand.

I still surprised when I see today's photographers complaining about the inability of today's cameras perform "miracles". Yes, the human eye is still superior to any means of image capture, when it comes to color reproduction and huge brightness variations in an image.


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## privatebydesign (Nov 16, 2015)

There are two things we are talking about here, clipping channels, and maintaining truer reds instead of them being orange.

First, Don's explanation is spot on for clipping channels, but the red is only truly lost when the red channel and at least one other are both clipping, if it is only the red channel that is clipped and turning to orange due to over exposure, but not clipping, of a second channel, we can adjust for that.

On the other hand I was talking about the general feel of the reds in the OP's first digital shot when compared to his film shot. Notice in that film shot the reds (the bars at the side of the Dunes sign) are not over exposed and so hold a true red, however the lights of the actual letters of the Dunes sign are blown with orange and gold showing through the less exposed parts. On the other hand if you look at other images of the Oasis tree trunks they are very red, not orange as in the OP's shot, so exactly the same thing has happened to the reds of the Oasis tree trunks as has happened to the tail lights in the digital shot, the red channel is blown and the green and blue channels are too high. The film has ressponded in exactly the same way as the digital sensor has.

Now, with regards the general orangeness of the reds in the digital shot, that is just profiling.

You can't apply a proper camera profile to a jpeg, but you can emulate it, so I have.

Here is the original digital shot, a version with a rough profile to address the red to orange shift and a gif of them both. I think you will agree the reds of the 'profiled' shot feel a lot closer to the film shot now.


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## JEL (Nov 16, 2015)

Don Haines said:


> Now overexpose by three stops to get some of the detail in the shadows.... 3 stops means 8 times the light. The red pixels are now receiving 800 percent of the light they can capture, green at 40 percent, and blue at 20 percent. The sensor reports the levels at 100, 40, and 20 and we get a different colour.



Thank you. Yes I agree with this 

But isn't this directly related to the color-filter's bandwidth?

Say the RGB channels were much narrower, then they should block light that falls outside their band-pass range much more efficiently, correct?
And in such a case, you should be able to over-expose the red channel more before you would notice a significant rise in the green and blue channel, correct?
(I'm not saying narrower color-filters are a good thing for color-fidelity, since, as somebody else mentioned, it might hinder yellow, magenta and cyan from appearing, but I'm still wondering if perhaps modern color-filters allow too much yellow, magenta and cyan through, in the hunt for increased low-light sensitivity. I don't have any gel-filters I could use to test this though, so it's just pure speculation on my part  )


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## rs (Nov 16, 2015)

JEL said:


> Don Haines said:
> 
> 
> > Now overexpose by three stops to get some of the detail in the shadows.... 3 stops means 8 times the light. The red pixels are now receiving 800 percent of the light they can capture, green at 40 percent, and blue at 20 percent. The sensor reports the levels at 100, 40, and 20 and we get a different colour.
> ...



But is the red from the light source a pure colour which falls only under what is considered red, a wavelength of approximately 650 nm? If so, then having a CFA on the green and blue channels which is strong enough to block out 100% of 650 nm light would result in a red light, no matter how it is exposed. But if the red is not pure, no CFA would stop the green and blue seeing something.


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## Don Haines (Nov 16, 2015)

rs said:


> JEL said:
> 
> 
> > Don Haines said:
> ...


The red light will not be pure. Incandescent bulbs, and to a lesser degree fluorescent bulbs, output a fairly wide spectrum of light. The paint or tinting to colour the bulbs will primarily let red through, but there will be a significant component of other frequencies.


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## JEL (Nov 18, 2015)

Ahh yes, good point. The actual emitted frequency... 
Well, I guess it makes sense that the camera-makers and film-makers spend much money on the color-science behind all this equipment we use 
It's interesting stuff, but probably getting a bit too geeky to continue discussing at this point for those of us who are merely laymen in this field 
Anyway, I guess the quest for better images will always be ongoing.

Thanks to all who participated in this thread.


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## rfdesigner (Nov 18, 2015)

JEL said:


> Ahh yes, good point. The actual emitted frequency...
> Well, I guess it makes sense that the camera-makers and film-makers spend much money on the color-science behind all this equipment we use
> It's interesting stuff, but probably getting a bit too geeky to continue discussing at this point for those of us who are merely laymen in this field
> Anyway, I guess the quest for better images will always be ongoing.
> ...



If anyone want's to see what a totally pure red looks like, if you ever get the opportunity to peer through a Hydrogen Alpha filter or SII filter (similar wavelength) you'll suddenly see (if the light source is bright enough.. it looks pretty dark).

First time I did it, I commented my eyes had run out of gamut!

After that even blood looks bright orange.


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## JEL (Nov 19, 2015)

Haha  I'll make a wish for an astronomy-camera, or at least an astronomy filter-set, for Christmas then 
Well, I guess it's good to know there's still room for improvement in our photo-technology  (that way I don't have to take all the heat for bad pictures  )


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