Johan, you said earlier that "If you want to get the 'colorimetric correct' white balance, you have to click on a point that must be neutral after you've set the white balance." I am still not clear about what you mean because it seems that I can read it in different ways. You use the work after, but how was the white balance set first? Are you saying you need to include a neutral grey card in the picture first and then use the eyedropper on it? If so, then w/o a grey card, our only choice would be to adjust the Temp and Tint sliders?
Yes. Think about the following situation. You work in a studio, and you need to be sure that your final photo has an exactly correct white balance. No room for personal taste, because the products your are shooting need to have the exact same color in your photos as they have in real life. What you do then is the following: In your first photo you include a special grey card. So you know that this card should be exactly grey in your photo. So you use the white balance eye dropper and click on this card. That will set the white balance to such a value that a card you
know is perfectly grey in real life, is now also grey in your photo. Then you use this white balance for the whole series.
Just posted the questions above before receiving Anjikun's message. When you click on that neutral card included in your shot, do you always get the same RGB values no matter the lighting was like?
Correct. You don't know the
shade of grey (that depends on the exposure), but that is not important. What is important is that you will always get grey; meaning the same values for R, G and B.
So if I can't find a spot (in non-studio shots) that's neutral, then the only resort is to play with the Temp and Tint sliders and guess at the correct balance?
Correct again. If you really cannot find any spot in the photo you think should be pretty much neutral grey, then the only thing you can do is use the sliders until you get something you like. In reality, there are more grey spots in a photo than you would think. Concrete or tarmac, for example. The lower part of a cloud. Those are spots you can try and often give you a pretty good starting point. Of course you can always use the eyedropper first, and then change the sliders if you don't like the result.
If I do find a spot in my image that give me the same RGB values, then click on it with the eyedropper will get me the correct overall WB
NO! Forget about looking for the same RGB values. That is senseless. I said before; a spot that has the same RGB number
right now, is not necessarily a spot that
ought to be grey. I gave you the example of a light blue shirt in yellow light. That shirt is really blue, but because of the yellow light
it looks grey right now. If you click on that shirt, nothing happens with the current white balance setting, because clicking on a spot will neutralize it, and this spot is already neutral.
You must not click on a spot that is neutral right now, you must click on a spot that should be neutral.
I always thought that was correct and it's what you do with the grey card.
The point is that the grey card is not grey if the white balance of your photo is not correct yet. You click on it to make it grey, by setting the correct white balance.