Is Lightroom WB tool Accurate?

[george013]

After reading some of the responses, I'm not convinced that everyone quite understands how the WB tool operates. For practical purposes, I used ACR instead of Lightroom to show what is happening. The ACR interface is less messy and I'm not sure if one can drop sample points in LR.

First up is an image I shot this morning using a halogen (tungsten) light source using a WhiBal card. The colour balance setting was tungsten:




It's not hard to see that there is a colour cast that is orange, i.e. the red and blue values are incorrect. The sample point I use is near the centre of the target.

After clicking the white balance tool on the target, this is what I get. The neutral target gives (nearly) identical values for R, G and B. This means the image has the proper white balance set.





So the "secret of success" using the WB tool in ACR or Lightroom is to pick a sample area that is neutral gray; in theory, any material that has equal values of R, G and B. If your sample area is not truly "gray" you will introduce a colour cast into the image. If one gets inconsistent results, its because the sample area being clicked on is not neutral.

The other thing I wanted to demonstrate is the relative uselessness of trying to set a colour temperature. One might be close in a studio when using studio strobes or a speedlight, but getting the colour temperature right anywhere else would be a fluke, nothing less. The only way to get a proper colour temperature reading is to buy a fairly expensive colour temperature meter from a company like Sekonic or Gossen,

I understand what you're doing and completely agree with you. But why is in photography warmer more red while it is warmer more blue.

George

[Manfred M]

I understand what you're doing and completely agree with you. But why is in photography warmer more red while it is warmer more blue.

George

It's not more blue, but rather too little blue.

If you look at the colour values of the original I have:

R = 98
G = 89
B = 69

We always have to look at the colours and their complements:

Red / Cyan, Green / Magenta and Blue / Yellow. Excessive yellow is the same as not enough blue, excessive red is the same as not enough cyan, which we see in this case. If we dial back the individual R, G and B values equally in the colour balanced image, we lighten the shot, if we increase the values equally, we darken the shot.

[Simon Garrett]

In photography, based on human emotion and experience, we tend to think of red/orange being associated with warmth - fire, sunlight etc. And we think of blue being cold - we associate blue with cold.

But white balance is usually related to so-called black-body radiation. When you heat a body - any material - it glows with a band of wavelengths with peak intensity at a characteristic colour. The colour is associated with the temperature of the body radiating heat and light, and goes from red to yellow to blue as it gets hotter. Think what happens to a tungsten light as you increase the power with a dimmer: the greater the power applied, the hotter the filament gets, and it goes from dim red-orange to yellow-white (it would probably break before getting to blue).

So in colour temperature, red is the cold end and blue the hot end - the opposite way round to normal human "feel" of colour.

Is that what you were asking?

[Nicks Pics]

In photography, based on human emotion and experience, we tend to think of red/orange being associated with warmth - fire, sunlight etc. And we think of blue being cold - we associate blue with cold.

But white balance is usually related to so-called black-body radiation. When you heat a body - any material - it glows with a band of wavelengths with peak intensity at a characteristic colour. The colour is associated with the temperature of the body radiating heat and light, and goes from red to yellow to blue as it gets hotter. Think what happens to a tungsten light as you increase the power with a dimmer: the greater the power applied, the hotter the filament gets, and it goes from dim red-orange to yellow-white (it would probably break before getting to blue).

So in colour temperature, red is the cold end and blue the hot end - the opposite way round to normal human "feel" of colour.

Is that what you were asking?

I think I've heard something along these lines. Have you ever noticed how the hottest flames in a camp fire are blue and the cooler ones are yellow? That I have heard is associated with it.

[george013]

In photography, based on human emotion and experience, we tend to think of red/orange being associated with warmth - fire, sunlight etc. And we think of blue being cold - we associate blue with cold.

But white balance is usually related to so-called black-body radiation. When you heat a body - any material - it glows with a band of wavelengths with peak intensity at a characteristic colour. The colour is associated with the temperature of the body radiating heat and light, and goes from red to yellow to blue as it gets hotter. Think what happens to a tungsten light as you increase the power with a dimmer: the greater the power applied, the hotter the filament gets, and it goes from dim red-orange to yellow-white (it would probably break before getting to blue).

So in colour temperature, red is the cold end and blue the hot end - the opposite way round to normal human "feel" of colour.

Is that what you were asking?

That was the question. Now the answer.
In Dutch there is a saying that if you are getting angry you are getting overtemperatured, hot. And if you are very angry you're wihite-hot angry. Comming from heating iron, it first gets red and white.

It's not just a feeling, there is also a temperature scale, black box hot 10000 is blue, photography 10000 is red. There must be more.

George

[DanK]

Wikipedia has a very clear explanation of this, including the fact that the relationship in physics, used in photography, is the reverse of the common psychological notion of warm and cold colors.

[xpatUSA]

And here is an in-depth article about Spanish daylight:

http://www.usna.edu/Users/oceano/ray...O_CCTpaper.pdf

From which I get that "accuracy" of WB is not real important for cameras sold world-wide?

Meanwhile let's not forget that other component "tint", the lines normal to the locus below:


[edit]
Didn't mean this post to be a thread-stopper, so I'll explain a bit more about the above. The diagram is similar to part of the traditional CIE 1931 xyY gamut diagram, which itself often used to show how "small" the sRGB gamut is and how so much "bigger" Adobe (1998) is. The above diagram serves the same purpose but u,v replace the x,y axes. These axes are more representative of how we see color differences. Now we see that "daylight" D55 lies not on the 'black body' locus but a bit above it - while still retaining the color temperature of 5,500K. This offset away from the theoretical black body can be called the "tint", if you like. Note also that the "old" CIE illuminants 'A' and 'C' are quite a bit below the locus.

A long time ago in a previous life here, I asked: "what is the correct WB setting for a light source?" - by which was meant, for example, a luminous watch in the dark or a traffic light on an unlit street. No need to answer that question here.

To my own satisfaction, I worked the correct WB out to be Illuminant 'E' above. Which you can only get if your camera provides CCT/tint as a WB option. Alternatively, you could shoot RAW and select "As Shot" in ACR and set 5500 in the temperature slider and so much on the tint slider. I used to know, but I can't remember how much the tint slider moves to get to 'E'.

Which is a pity, because no less a personage than Eric Chan (the ACR man) told me.