White Balance vs Color Temperature

[Megan]

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Hi,

I have a question about the manual white balance setting on Leica Q.  On Leica Q, the higher the value,  the warmer the color while on a color temperature chart like an LED, the lower the value the warmer the color. Does anyone know why?

Leica Q white balance: from cool to warm: 2000K-11500K

Color temperature chart, from warm to cool: 1500k - 6500K+

Hope someone can shed some lights. Thanks in advance!

[Jared]

Sure.  A color temperature chart shows the color of light that is produced by a black body radiator.  Basically, what color something glows if it is heated up to that temperature.  It’s not quite that simple (since all colors are actually emitted and not all objects behave as perfect black bodies when heated), but you get the idea.  Heat up some iron in a forge and it glows red.  Heat it up more and it glows yellow. Heat it up more and it glows white.  Get it even hotter and it would glow blue.

The white balance in a camera is the exact opposite since it is showing not the color of the light, but the color adjustment that must be applied to make it look white under a given color of light.  For example, if something is lit by tungsten light (very yellow), you need to add cool blue to make it look white.  So the camera’s white balance is the adjustment to get something back to white.  If you are under warm light you need to cool it off.  If you are under cool light like shade, you need to warm it up.  So the higher the color temperature of the light, the warmer the adjustment that is made.  The lower (warmer) the color temperature of the light, the cooler the adjustment that must be made.  They cancel out somewhere around 5500 Kelvin which is the “white” of open sunlight (the sum of the yellow the Sun looks due to atmospheric scattering and the blue of the sky which is the scattered light).

So the Q cools off low Kelvin numbers and warms up high Kelvin numbers to make everything come out in the middle.

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[adan]

To complement what Jared said:

Color temperature is a measure of lighting color. In the era before LEDs, we got our man-made light from a heated wire (or flame), and the hotter the wire or flame, the bluer it was, and the colder the wire or flame, the yellower/redder it was (although still physically hot enough to burn one ).

The surface of the sun - from which we get our daylight, and under which we evolved - is about 5778°K, thus "normal daylight" is in the range 5500°-6000°K.

Generally, wires or flames as hot as the sun would be fire hazards (and generally beyond our technology until just a couple of hundred years ago), thus man-made lighting operated at the lower, yellower temperature of candles (1228°K) or bonfires (2000°K) or heated tungsten wires (2000-3000°K). Wasn't a big deal until we humans began trying to take color photographs.

Photofloods (250-500W) or flash bulbs burn at about 3200°K - and for pictures on daylight color film, came in a blue-coated version to raise their effective color temperature to "look like" the sun - 5500°K.

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White balance is the inverse of color temperature - it is the balancing of that lighting color to get rid of its excess yellow or blue and make things look "natural" - i.e. as they would under normal direct sunlight. You set your WB to 2200°K (very blue) to balance (make neutral) a lighting source of color temperature 2200°K (very yellow). Just like adding that blue coating to the flash bulb above. (And as the Q's scale shows).

Or conversely, after sunset when the light itself is very blue (say, 10000°K - no sun, just the glow of the purple sky), you move the WB to 10000°K to balance all that blue with added yellow (as the Q's scale shows).

Unless, of course, you want that excess orange/yellow or blue, to reproduce the "mood" of the time of day or location. Blue dusk, orange fire/candle light, yellow room light.

 

Edited August 22, 2019 by adan

[evikne]

What about the green/magenta tint that we can adjust in LR and other imaging applications? Is this color tint only caused by reflections from the surroundings?

Edited August 22, 2019 by evikne

[jaapv]

The light we record on our cameras is nearly always reflected light. It is rare for the light source to be the subject.

[adan]

59 minutes ago, evikne said:

What about the green/magenta tint that we can adjust in LR and other imaging applications? Is this color tint only caused by reflections from the surroundings?

Not necessarily. It is more for spectral correction outside the strictly yellow-blue color-temperature continuum (such as from fluorescent-tube lights, and these days from some wacky LED effects - I shot an LED-illuminated night event 4-5 years ago, and even with supposedly-matched RGB LED units to make "white daylight," they still came out grievously purple-white.)

You can have green-yellow and orange-yellow lights - both of, let us say, 2500°K yellowish color - and the one-dimensional color-temperature "yardstick" (or meter-stick) can't do anything to match them without the option for the "tint" correction. Think of it as a separate yardstick at 90° to the blue-yellow yardstick, so that you can sidestep the color correction more precisely.

[evikne]

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I think color temperature is interesting. I posted these two pictures here in the forum the other day. I used an ExpoDisc to sample the color temperature for each shot to achieve as natural colors as possible. Both pictures were taken within a few minutes, but in opposite directions: one in direct evening sunlight, and the other towards the sun, but in the shade behind a boathouse. It's interesting to see how different the light is in the two pictures.

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[Jared]

7 hours ago, evikne said:

What about the green/magenta tint that we can adjust in LR and other imaging applications? Is this color tint only caused by reflections from the surroundings?

The color temperature assumes the light is coming from something hot that glows,  it broadly emits like a black body (physics term for the exact ratios of electromagnetic radiation emitted by objects at different temperatures).  A tungsten lightbulb may peak in the orange/yellow part of the spectrum, but it emits some red, green, and blue as well.  The Sun may peak in the green portion of the spectrum, but there is plenty of red, yellow, blue, and violet.  

However, many light sources don’t create their light that way.  A neon light, for example, emits primarily one specific color of red.  Many astrophotographers will photograph objects in HII (ionized hydrogen), OIII (doubly ionized oxygen) and ionized sulfur.  A fluorescent lightbulb emits only specific, narrow ranges of colors.  The “tint” lets you correct for these light sources that don’t match up with a specific color temperature.

[antigallican]

Great thread!

[Megan]

Thank you everyone for chiming in, especially Jared and Adan for all wonderful details. 

After reading all the replies, I still have some confusion about the Kelvins so I went to my best friend Google  and got it clarified.  Here is my understanding, please correct me if I am wrong. Basically white balance Kelvin value is what you tell the camera the ambient color temperature is,  just like the presets.  The algorithm camera uses always assume you want neutral sunlight , i.e. ~5500K. Therefore the lower the Kelvin value on white balance, the more blue camera will add. The higher the Kelvin value is, the more yellow camera will add. That's why under neutral sunlight ~5500K the image will appear blue if you tell camera it's 2200K instead and will appear yellow if you tell camera its 9000K. 

Thanks again everyone, really appreciate it!

 

Edited August 22, 2019 by mbaocc