deronsizemore wrote in post #13427913
Ok, so using the WB too, i.e., white/gray card calibrates to a full cup of RGB. RGB values will be good to go using a WB tool, correct? After that, you lost me...
When you shoot a white or gray "target" for White Balance, it's not about getting a "full cup" of RGB, but rather it's telling either the camera or your Raw processing softare that "this target is gray", meaning it has equal values of R, G and B. In fact, you don't want to have say a white target "clipped", you just want to give a good exposure to a neutral target, whether white or gray. If you use an automatic exposure mode, the camera will attempt to bring the white down to gray or a darker shade up toward the left-center of the histogram.
You can see in your Raw software what happens to your RGB values -- have a shot with a "target" and set the shot to an "off" White Balance, say tungsten when it should be daytime, or whatever. Put your mouse pointer over the neutral target so that you can see the RGB values. You should see that those values are not equal, since you have thrown your White Balance off.
Click the target with the White Balance eyedropper and you will see the values change to pretty much be equal.
I see. So you can get proper WB/exposure with either a gray card card or white card, but you recommend the white card because it's easier to get a reading because it's lighter. When you're setting exposure, you recommend to open up about 2-1/3 stops to start to chimp the exposure to the right. What if you're already wide open as an example? Do you then start bumping the ISO higher?
Well, you are talking about two things here, White Balance and exposure. The White Balance target can be white or gray, as long as it's really neutral. You don't have to fuss about exposure with it, just put your lens in MF, fill the metering circle with the target, and take the pic.
For your exposure question, that's a different topic. Yes, you want to get whites up over +2 EV if the light is good and you have the ability. You set your aperture and shutter speed to be optimal for the scene. If you still need to up the brightness, yes you can use a higher ISO -- you will bet better results than if you underexpose the scene and try to boost it in software/post-processing.
In regards to RGB values, how do you blow one/all out? Maybe if I understood that, I would start to understand this as a whole. Is it dependent upon the colors in the photograph? So if the shot is overexposed and the white spike is falling off the right side of the luminance histogram, that in turn blows out the Red value (because of the red shirt on the subject as seen in the "how not to expose to the right" from Curtis N?). If that's not it, I'm afraid I'm just not getting how you can expose to the right with the spike on the right not falling off the histogram but still blow out an RGB value. I'm not seeing the relationship.
Well, this can be more complicated, because when you are shooting a colorful subject, it's possible to "clip" one color channel but, because you aren't "blowing out" highlights, only one channel is clipped and so the Luminance histogram won't show this. The data won't overflow the right edge. But, if you switch to the RGB histogram, you will see the clipped channel. You then have to figure out how to handle this.
There are a few approaches to managing colors here. First, you use the RGB histogram!
Then, it can help you to do one or more of the following:
First, you can set your Picture Style to Neutral, and then in the Picture Style menu, set both your Contrast and Saturation all the way back to -4. This will keep the camera from giving you a "false" reading of clipped colors (as well as blown highlights).
Then, things can get more complicated!
One fact is that the sRGB color space, which is our "universal" space because most people and monitors and printers use that space, is a "narrow" color space compared to the common alternative, which is Adobe RGB (aRGB). And then, the camera sensor can actually capture an even wider range.
If you set your camera to the sRGB color space and avoid clipping a channel, you are "safe" and then would process your shots in a "normal" way. But, if you set the camera to shoot in aRGB, you will have a bit more "room" in your exposure of bright/saturated colors. You can "push" things a bit so your overall scene can get a better exposure.
This can be useful, but you need to realize that if you do push a color to the right edge of the RGB histogram using the aRGB space, then if you look at it in the sRGB space that color will be clipped.
This means that in post-processing you'll need to "tame" that color if you want it to be properly presented for, say, a Web display or other "generic" presentation.
Lastly, there is the "UniWhiBal" technique, which can be, well, interesting. I for one have only messed with this a little.
It's based on the fact that half of the sensor "wells" are actually filtered to collect green light. The other half are divided between Red and Blue. The camera then uses your White Balance and Color tone settings to render an RGB image for your Preview and histogram.
This can be fine for most scenes, but when dealing with color extremes like we've been talking about, a "normal" White Balance can throw things off, giving misleading readings. So the UniWhiBal approach has been developed, in which you set the WB to reflect the greater amount of green compared to the reds and blues. The resulting images are, well, "garish" is a word that could be used. Then, in your Raw software you can set things more in order, which can be done using a gray target or a WB preset, or of course you can do it using the controls.
The way people set the in-camera WB for this is by either using a specially developed image for the Custom WB or the "easy" approach -- take the custom WB shot with the lens cap on and use that to set the Custom WB, The result will, as I've indicated, produce "greenish" images.
Well, that's all I'm gonna say about that. As I've said, I've only messed with the UniWhiBal a bit, never in my "normal" shooting. In fact, for my normal outdoor shooting I use Auto WB -- I always shoot Raw and so can correct things easily if needed. If I'm shooting indoors without a flash, I can shoot a WB target, or even with a flash, but actually I've found that Auto WB works quite well for the flash stuff I do, but I don't do studio work that requires "perfect" color. In fact, when I do indoor shooting that needs flash, I generally open my exposure to let as much ambient light as I can, so that a "good" WB will be some sort of mix anyway and even using a target could throw things off.
Anyway, I hope I haven't bored y'all!
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