AWB, Kelvins - How do I properly use them in manual mode to get a good light setting

[Colin Southern]

Wonderful stuff Richard

Just the tiniest of nit-picks ... I'm told that we're supposed to say "kelvin", not "degrees kelvin" Can't say I understand why, but then again, I don't understand a lot of things!

[purplehaze]

Except for shooting under extremely mixed lighting conditions, I always shoot RAW and use AWB to get me close to the color I want and then tweak that color in Camera Raw.

Great post, Richard, especially the stuff about filters. I must say that one of the things I love about my Canon S95 is that I can fine tune any given white balance on both the b/a and the g/m axes and see the results live in the LCD monitor as I'm doing so. Instant feedback, before I press the shutter! It is a very useful feature for those mixed lighting situations when I want to be sure to get the colours of my subject just so. I wish I had it on my Nikon D90.

[purplehaze]

I'm told that we're supposed to say "kelvin", not "degrees kelvin" Can't say I understand why, but then again, I don't understand a lot of things!

Because I'm a word nut, I had to check, and you're both right. "Kelvin" is the SI unit equivalent to "degree Celsius". However, my dictionary of science states "formerly 'degree Kelvin'".

[insidescoop]

IThanks so much! Very helpful reply!

[rpcrowe]

By the way... When shooting RAW, especially, AWB does a very satisfactory job. I seldom if ever shoot any other way...

[Colin Southern]

By the way... When shooting RAW, especially, AWB does a very satisfactory job. I seldom if ever shoot any other way...

I find it seems OK for the likes of general landscape, but for closeup portraiture it's never "spot on" (it might look OK initially, but once the correct numbers are dialed it one can usually see a significant improvement).

[Peter Ryan]

My science teacher – my partner tells me there is no ‘degree’ in Kelvin. Whether there is or there isn’t I think it confuses people. I see the Kelvin scale more as a colour chart (like a paint chart) rather than a hot or cold measurement. If you can visualise the RGB colour spectrum the Kelvin scale runs from Red through Orange, Yellow and across the middle of the spectrum to White and on to Cyan and Blue. Most of the colours on the scale from Red to White are from direct light sources (man made or direct light from the sun) while the blue colours come from indirect light reflected from the sky above.

The Tint slider in WB correction covers the other axis of the colour spectrum ‘Green – Magenta’.

With landscapes Auto WB is ok, as long as you don’t have mixed light sources. If you are shooting an open scene in sunlight then the area is lit by direct light and the auto WB is generally ok.

If you are shooting in the shade (like a waterfall in a valley) then you are working with indirect light. You subject is lit by reflected light from the sky and will give a blue cast, particularly with longer exposures. Again your Auto WB should work ok if all your shot is in the shade.

If you are shooting a subject in the shade (indirect light = bluish cast) and have a background in the sun (direct light) then the auto WB tries to average the two sources of light and gives a poor result. You need to choose what is important and set the WB for that or correct in PP. ACR is your best bet but if you correct the main area you are likely to overly correct the other and you cannot mask for WB corrections in ACR so you might have to correct the main subject area and then mask the secondary area in PS for some small colour correction.

Having said Auto WB generally works OK I use a Nikon, shoot a lot of landscapes and find it shoots a little on the cool side (bluish) – around 200 on the Kelvin Scale but you need to work through this with the light in your location.

Edit: One definite adjustment is to shoot sunrise and sunset on the Cloudy setting. These are red/yellow in colour and the camera adds blue to bring it back to a neutral white light and washes out the colour. By choosing Cloudy you are telling the camera to add add a little red.

[insidescoop]

Thanks Peter!

[williamdsym]

Some great tips, I like to use Kelvin scale in live view trying to match up what is in front with the live view it seems to work for me

[xpatUSA]

My science teacher – my partner tells me there is no ‘degree’ in Kelvin. Whether there is or there isn’t I think it confuses people.

I don't understand why your Science teacher would tell you that!

https://en.wikipedia.org/wiki/Kelvin

So hopefully the link above will reduce the amount the confusion caused.

Oops, I missed the age of this topic.

Thanks, Urban!

[Inkanyezi]

The web sometimes is a powerful time machine.

So first, welcome williamdsym!

It was really an old thread you lifted from oblivion, and it does contain some tidbits that are useful, as well as a few that maybe would be better forgotten. Such is the workings of search engines, that you can find just about anything, provided you dial in the right search profile. And it is possible that Peter Ryan already had cleared up any confusion about degrees and Kelvin. After all, that was about five years ago.

But there are a few things there, some of which are important to photographers, and should perhaps be pointed out:

• K values, so named for the Kelvin degrees of a black body that emits this type of light, are fully valid only for black body radiation.
• The nearest to true black body radiators we have are incandescent bulbs.
• So in essence, there is no real difference between the Kelvin temperature of a black body radiator and its K value for colour.
• Anyway, when using the K denomination for a light source, no degree sign (°) should be used.
• Many of our light sources are not black body radiators.
• Daylight, fluorescent light, LED or other light sources that emit light in other ways than black body radiation are not representative for black body radiators, and their spectral properties mostly are different, so they should not be evaluated with the K scale.
• With digital photography, we have means to evaluate any type of light source by measuring the light reflected from a spectrally neutral reference. This method is often used to achieve a white balance value with which to start. References are not "gray cards", and most gray cards I have seen are not spectrally neutral. Gray cards were used in the past to evaluate exposure, for a reference of 18 % reflection of light. They were not made for white balancing.
• There are also a few light sources that cannot be white balanced, mainly because their light is not white.
• White light is a mixture of wavelengths that contains sufficient amount of the three spectral bands to which our eyes are sensitive.
• Neither light emitted from a light source, nor light reflected off a surface has colour, they are only mixes of wavelengths (frequencies) in the physical world.
• Colour is not a physical property. Colour is a subjective perceptual response to light. The properties of colour reside in our brains, as an interpretation of the image captured by our eyes. Some wavelengths are seen as red, other as blue, and yet other wavelengths are seen as green.
• We can also interpret mixes of wavelengths in different bands as yellow, magenta and cyan colour, as well as lots of mixes of those colours.
• In fact, also true spectral wavelengths between the tops of our vision cells' sensitivities are interpreted just as the mixed colours, as our perception is based on mixes of red, blue and green. Hence the yellow band we see in sodium light is received as input from both our red and green receptors in the eye (as there is no yellow receptor).
• But colour itself is only in our imagination, and we can never know how other persons perceive the same mixes of those wavelengths, even though we may call the colours by the same names or even reproduce them.

One very useful item for a photographer is a reasonably neutral white reference, to be used for setting white balance, in the camera or in post production when converting the RAW file.