White Balance Question

[Matthew Cernohorsky]

So...white balance will make a grey object grey under any lighting, and therefore other colors will be shifted to make them true to life also. Does this mean that if I have an entire tungsten lighting set-up, I white balance it properly, record an.......(apple) and then I replace every light with fluorescent bulbs (or whatever other light I want) and re-record the exact same scene (again properly white balanced), that the apple and its surroundings will appear EXACTLY the same as the first shot? I'm sure this is not the case and that that there would be some kind of difference. I guess I'm asking what exactly that difference is. If that is the case, then why on earth would I want to have bulbs of different color temperatures for my (insert light here)?

EDIT: Of course their could be reasons like having multiple color temperatures in a scene, but for this scenario, I'm assuming it's a scene with a single color temperature.

 

[Graeme Nattress]

Different light sources have different spectrums, and hence will not just differ in colour temperature. So, even our eyes after adapting to the different colour temperature will see the new scene a little differently.

Graeme

 

[Matthew Cernohorsky]

Thanks! Helps so much! Thats makes a lot of sense. So what is the technical difference between a properly white balanced daylight seen and a properly white balanced candle-lit scene? What makes me instantly say "That's sunlight," right away? Or is there not really an answer to that?

 

[Graeme Nattress]

Mostly colour temperature, but also the size / softness / angle of the lighting too. In terms of artificial light, the spectral response will show more - the green spike of fluorescents for example over the continuous smooth spectrum of tungsten, say.

Graeme

 

[Matthew Cernohorsky]

Very helpful. Thank you.

 

[David Mullen ASC]

Even though tungsten (3200K) and HMI's (in the 5600K ballpark, they can vary quite a bit) are considered "full spectrum" sources (meaning they contain all the wavelengths of different colors), and even some fluorescents are considered "full spectrum", they are not all the same, some can have spikes in certain wavelengths and be weak in others. Also, film stocks and sensors favor some color temps more than others, and even some specific shades more than others.

The real problem, from a cinematographer's standpoint, is that tungsten, as a source, is fairly consistent and full spectrum, it's just at the low end of the color temp range and relatively power-inefficient. But other types of lamps have all sorts of color quirks to them, particularly a problem with excess green that varies as the unit gets warmer. So from a real-world perspective, the problem with a lot of lamps is that the color variations and wavelength spikes and weak spots can cause the color of an object to be rendered inaccurately.

The other problem is from the camera and image processing side of things, how the camera actually "white balances" the image, if information is weak in certain color areas, it can be hard for some cameras and processors to boost that information in a completely linear fashion without artifacts, to achieve a neutral image.

A good example is if the off-balanced image was recorded in 8-bit 4:2:0 video with a high compression rate, there will be limitations in how much you can play around with the color levels to achieve a neutral color balance -- because too much color information was tossed out in the recording format, and what's there is highly compressed.

 

[Matthew Cernohorsky]

While we're on the topic, I might as well ask: Is it an acceptable practice to use an “incorrect” white balance as an artistic tool while grading under certain (rare) circumstances? (Or is it always better to use conventional grading tools?)

 

[David Mullen ASC]

Sure, if it works.

For example, I shot a movie called "Northfork" all on tungsten-balanced film stocks in daylight-balanced lighting without the corrective filter, thus ending up with a very blue-ish image on the film negative. I timed some of that out in post, leaving a faint blue cast, but one of the side effects of not using the correct filter was that the red layer was underexposed compared to the blue and green layers, so skintones were somewhat desaturated, which is what I wanted.

With digital color-correction, it's all about what sort of information do you want to drag into post with you, and what do you want to leave behind or what can you live without, because if it's not there in the recording, it's not there to play with in post.

One example of playing with color with post in mind -- sometimes people do a scene in all red lighting, like for an old-fashioned darkroom scene. Trouble with that is that objects don't look very sharp under red lighting, particularly when shot on color film since red is one of the softer layers (or if recording to a 4:2:2 or 4:2:0 / 4:1:1 video format). So some people will shoot a scene like that under magenta (red + blue) lighting instead of red so that there is some information in the blue channel as well as the red channel, providing a bit more detail and sharpness in post to play with.

Now if you want an "incorrect" color-balance for the final image, like a blue dusk or day-for-night scene, or an orange firelight or sunset scene, or a greenish fluorescent-lit scene, then go ahead and shoot the scene that way under that kind of light, there's no law saying that you always have to start with a neutral image in the final color-correction when you want a strong colored tint in the final image. Just keep in mind that it's harder to change your mind if you go too far in terms of baking-in a strong color cast. But I say, be bold with color, it's the only way you really learn to use it as an artist.

 

[Sam Eilertsen]

While we're on the topic, I might as well ask: Is it an acceptable practice to use an “incorrect” white balance as an artistic tool while grading under certain (rare) circumstances? (Or is it always better to use conventional grading tools?)

You mentioned candle-light. Candle-light and other forms of fire light are typically not white-balanced "correctly" (eg to white). We do not generally see fire as white, we see it as yellow or orange, so it is typical to let fire-light be orange.

 

[Matthew Cernohorsky]

You mentioned candle-light. Candle-light and other forms of fire light are typically not white-balanced "correctly" (eg to white). We do not generally see fire as white, we see it as yellow or orange, so it is typical to let fire-light be orange.

When I say white balanced correctly, I mean white balanced to a grey card so that neutral objects are rendered neutral, not so that the lighting source (in this case candle-light) is rendered neutral. It is possible to white balance a candle-lit scene. Not that you don't know what you're talking about. Just possibly a misunderstanding. But that's a good example of a scenario where I may want to offset the colour temperature slightly to give a warm look. I was just wondering if that is ever done in feature films. (Thanks David)

These forums are great. Everyone is very helpful.

 

[peteb]

What a great thread, I've found the info here really informative.

Thanks for posting.

Pete B