I'd like to tell you about a discovery I made yesterday. It won't be of much use to most members or for most photos, but it may be interesting for those who are interested in the more esoteric aspects of Raw processing.
First, a bit of background. When shooting landscapes and nature, including flowers, (in the Middle East it is already the beginning of Spring and the wild flowers are starting to bloom) I shoot with the camera set to the Uni-WB custom white balance. [For anyone not familiar with the term, the Uni-WB is a sort of anti-WB, a trick to prevent the camera from doing WB to the LCD jpg or the Live View display.]
Because the native, unbalanced color of a digital image has a strong green cast to it, the first step in my Lightroom workflow is to apply a WB in order to turn it into a more normal looking image. For this reason I have set up LR with an import preset that does nothing other than change WB from the default "As Shot" to "Auto", so on the computer I never see that green image and starting from "Auto" I tweak the WB to taste. But yesterday, while trying something unrelated to WB in DPP, I opened a shot of a red flower, shot with my 100 f/2.8L macro lens, in which the flower filled the entire frame - no other color there except various shades of red. And, of course, DPP opened it with the "As Shot" settings. The photo looked great, although in LR I had been having the problems that any shooter of red objects knows, WB often causes the red channel to clip in what seems at the time of shooting to be a properly exposed photo.
To confirm what I thought was happening, I opened the file in Raw Digger to see the Raw histogram. Normally, in a photo that contains a wide spectrum of colors, because the sensor is most sensitive to green, the green channel will be more exposed, i.e. more to the right, than the other two channels and one of the functions of white balancing is to beef up the relatively weak red channel. But in this case all the light reaching the camera was mostly red. There were still green and blue components in the light, but it was the red channel that was most exposed. I wasn't dealing with normal sunlight or any other "normal" lighting, and, therefore, WB not only wasn't needed, I was better off without it. I went back to LR and changed the WB to "As Shot" and was much more pleased with the rendering.
Of course this was a special case and few people will want to use the Uni-WB in their cameras. But I have noticed that in LR when it is set to "As Shot" the two WB sliders go over to the extreme left, 2000 and -150. I don't know if that really represents a null WB or the sliders just can't go any further left, but it does create a display that is quite close to what I see in a camera-created jpg with Uni-WB. So I'd advise that if you are in a similar situation, light that is strongly biased to one channel, almost mono-chromatic, try 2000/-150, you might like it.
