Clear up white, gray and black cards for me

tonylong wrote in post #13428242
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.

So, does the WB have more of an effect on the RGB values than exposure? If your white balance is off, then your RGB values will be off and if you've exposed to the right in the luminance histogram but the right spike is overflowing the right hand side, that will in turn clip one (or more) of the RGB values?

I know you also said that one of the RGB values can be clipped even with a good exposure, but is the above scenario the most common?

tonylong wrote in post #13428242
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.

Setting aperture and shutter speed to be optimal for the scene, is that a trial and error thing for you? I.e., switch to manual, allow white card to fill the frame, adjust exposure until meter needle is in the middle, snap a shot, review histograms, re-adjust aperture and shutter speed to get right spike near the right-side on luminance histogram? Or, do you use live mode (as someone else suggested here) or other?

tonylong wrote in post #13428242
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!

Thanks for the detailed explanation of all of this. I'm going to re-read it tomorrow to let it sink in more but it makes sense, I think.

deronsizemore wrote in post #13428900
So, does the WB have more of an effect on the RGB values than exposure? If your white balance is off, then your RGB values will be off and if you've exposed to the right in the luminance histogram but the right spike is overflowing the right hand side, that will in turn clip one (or more) of the RGB values?

To me, the first sentence is kind of the long way 'round way to think about it. On the T2i (not sure if the T1i has this) you can display an RGB histogram. With this, it's clear that in actual scenes the three individual color histograms do not match the luminance/white histogram (which is a composite of the three). Often the red goes farther to the right than the white does. So you can have a non-clipped white histogram, but when you look closer at it with RGB values, the red IS clipped. And if you're using that supposedly unclipped white spike for your WB, the calculations will be skewed by the hidden clipped color.

True white, black and gray are all devoid of color. IF they are true white, black, or gray. If so, any of them can be used to achieve a true white balance.
Use the gray card for exposure. Never use a white or black card for exposure.
All a white balance does is tell the camera what ‘no color’ is. If you WB on a slightly red card you will get a ‘cold’ WB since the camera will attempt to remove the red. If you WB on a slightly blue card you will get a ‘warm’ WB because the camera will try to remove the blue.
Never try to set a WB with a clipped white.

AntonLargiader wrote in post #13429875
To me, the first sentence is kind of the long way 'round way to think about it. On the T2i (not sure if the T1i has this) you can display an RGB histogram. With this, it's clear that in actual scenes the three individual color histograms do not match the luminance/white histogram (which is a composite of the three). Often the red goes farther to the right than the white does. So you can have a non-clipped white histogram, but when you look closer at it with RGB values, the red IS clipped. And if you're using that supposedly unclipped white spike for your WB, the calculations will be skewed by the hidden clipped color.

On the T1i, I can display the RGB and luminance histograms side by side when reviewing a shot. To better understand this, what do I have to do in a test shot to ensure my luminance histogram has a spike on the right (but not clipped) but one of the RBG values is clipped? Maybe if I could setup a shot and get a nice spike on the right in the luminance histogram but blow out a red channel, I could see why it happened and understand better. Right now, I keep thinking the luminance histogram is an indication of black, gray and white in the photo. So, given a perfect luminance histogram, I can't in my mind figure out how you could blow an RGB value with a perfect luminance histogram.

You mentioned:

So, I've set WB using a shot of a gray/white card. I then set exposure using the white/gray card and adjust exposure until the spike is on the right but not clipped. How then could that translate into a hidden clipped RGB value?

1shot wrote in post #13430885
True white, black and gray are all devoid of color. IF they are true white, black, or gray. If so, any of them can be used to achieve a true white balance.
Use the gray card for exposure. Never use a white or black card for exposure.
All a white balance does is tell the camera what ‘no color’ is. If you WB on a slightly red card you will get a ‘cold’ WB since the camera will attempt to remove the red. If you WB on a slightly blue card you will get a ‘warm’ WB because the camera will try to remove the blue.
Never try to set a WB with a clipped white.

Thanks. Seems that there's many different techniques and thoughts on this. A lot of said to only use a gray card while others say to use a white card exclusively. I guess I'll just have to test some myself and see the outcomes.

You CAN use a white card for white balance, but it's much easier to accidentally overexpose one (or more) of the color channels without realizing it. If you're shooting your test shots on a white card, your natural inclination is to try to get a "proper" exposure of that white, which puts the histogram spike right next to the white edge. And if the combined spike is right next to the edge, it's possible that one of the channels is falling off the edge, and your WB corrections will be wrong, as discussed above.

For white balance purposes, if you underexpose your white card so that the histogram spike is NOT right next to the right edge, then it's safe to use it.

if you have a gray card, your natural inclination is going to be to put that spike right in the center, so it's much less likely that any of the three channels will be clipped off the right or left.

deronsizemore wrote in post #13431306
So, given a perfect luminance histogram, I can't in my mind figure out how you could blow an RGB value with a perfect luminance histogram.

Your post makes it sound like you're trying to create that condition as a test. It's not hard; you just need a scene with excess red such as a typical indoor, tungsten-lit environment. Dimmed incandescents should do it. I just shot a white sheet of paper using my desk lamp with a 60W bulb. I exposed so as to put the luminance spike to the far right without any blinkies. Here are the four relevant histograms from Photoshop:

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PhotosGuy wrote in post #13420575
White paper exposed on the meter will come out gray in density in the LCD image & the peak should be in the middle of the histogram. That's the "it".
The actual color may be off as you haven't set the custom WB yet, but that doesn't matter. What matters is that the RGB values aren't blown out.

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?

The question has been well answered, so just a point of interest: Usually, first set the f-stop OR shutter speed you need for the effect you want. Then the other parameter: shutter speed or f-stop. Then adjust the ISO. BUT, sometimes I'll set the ISO first, depending on the situation. There ain't no rule that can't be broken.

1shot wrote in post #13430885
True white, black and gray are all devoid of color. IF they are true white, black, or gray. If so, any of them can be used to achieve a true white balance.
Use the gray card for exposure. Never use a white or black card for exposure.
All a white balance does is tell the camera what ‘no color’ is. If you WB on a slightly red card you will get a ‘cold’ WB since the camera will attempt to remove the red. If you WB on a slightly blue card you will get a ‘warm’ WB because the camera will try to remove the blue.
Never try to set a WB with a clipped white.

Never say never! In fact, Kodak recommends using the white side in low light in the .doc that came with the gray card.

And unless you're shooting something like products on several days where the balance needs to match, then WB is a matter of taste, anyway. I usually prefer to push portraits just a touch to the warm side. And would you want to make a sunset neutral?

PhotosGuy wrote in post #13435135
Never say never! In fact, Kodak recommends using the white side in low light in the .doc that came with the gray card.

And unless you're shooting something like products on several days where the balance needs to match, then WB is a matter of taste, anyway. I usually prefer to push portraits just a touch to the warm side. And would you want to make a sunset neutral?

I would never use any card for exposure, be it white, black or gray. The only time I ever use a white card is for video when there are two or more cameras that must match each other.

Warning: the following is an opinion only and only holds weight with me.

Far too many people get into the technical side of photography and forget that is an artistic venture. I understand light and Kelvin temperatures so I usually dial in my white balance manually. I always shoot RAW (except when shooting something that will not be PPed) so I set my white balance and adjust to taste later in PS. My exposure is always set by eye or the histogram. If anything I will underexpose, and try to never over expose.
I would NEVER adjust a beautiful sunset to neutral. NEVER! Generally speaking, I always WB to the warm side anyway unless I have a specific reason to make it cooler.

p.s. I won a gray card and several white and black cards and have never used any of them for either exposure setting or WBing. YMMV

nathancarter wrote in post #13432001
You CAN use a white card for white balance, but it's much easier to accidentally overexpose one (or more) of the color channels without realizing it. If you're shooting your test shots on a white card, your natural inclination is to try to get a "proper" exposure of that white, which puts the histogram spike right next to the white edge. And if the combined spike is right next to the edge, it's possible that one of the channels is falling off the edge, and your WB corrections will be wrong, as discussed above.

For white balance purposes, if you underexpose your white card so that the histogram spike is NOT right next to the right edge, then it's safe to use it.

if you have a gray card, your natural inclination is going to be to put that spike right in the center, so it's much less likely that any of the three channels will be clipped off the right or left.

Thank you. Makes sense.

AntonLargiader wrote in post #13434815
Your post makes it sound like you're trying to create that condition as a test. It's not hard; you just need a scene with excess red such as a typical indoor, tungsten-lit environment. Dimmed incandescents should do it. I just shot a white sheet of paper using my desk lamp with a 60W bulb. I exposed so as to put the luminance spike to the far right without any blinkies. Here are the four relevant histograms from Photoshop:

Hosted photo: posted by AntonLargiader in
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forum: General Photography Talk

As you can see, the red is actually farther to the right than the luminance is. In fact, it is visibly clipped. And this is with a supposedly 'daylight' bulb!

The consequence of this when setting WB is that red is now underrepresented in the color mix. In this case it's not clipped by very much, and the resulting WB (when I set that frame as custom WB and shoot a properly exposed one) looks pretty good. But hopefully this illustrates the principle.

Ah! After all these posts, now it FINALLY sinks in. As a completely noob with all of this, I was thinking that to clip a red channel, the shot had to have something red in it. Maybe a picture of Santa Claus? His suit is bright red thus making it easy to clip a red channel. I wasn't getting that it was the LIGHT in the room/shot that clips a channel rather than what might be in the shot. I did a test just today (before reading your reply) where I took two artificial limes my wife had laying around, put them on the counter and took a picture. The luminosity histogram was good with a spike on the right, but the red channel was clipped just a bit and I was getting some blinking letting me know highlights were blown out. The shot had some brown tones from the counter and the limes were green. So, I kept thinking to myself: "how in the hell can the red channel be clipped!?"

After your explanation, it's obvious. It was the lighting in the kitchen. So, if you have your typical indoor, tungsten-lit environment and you expose to the right, chances are you could have a clipped red channel? In which case, you'd have to expose not so far right to get the red channel within the boundaries of the histogram? Is that assessment accurate?

Thanks for your help!

PhotosGuy wrote in post #13435135
The question has been well answered, so just a point of interest: Usually, first set the f-stop OR shutter speed you need for the effect you want. Then the other parameter: shutter speed or f-stop. Then adjust the ISO. BUT, sometimes I'll set the ISO first, depending on the situation. There ain't no rule that can't be broken.

Never say never! In fact, Kodak recommends using the white side in low light in the .doc that came with the gray card.

Gotcha! Thanks for hanging in there with me on this thread.

deronsizemore wrote in post #13447840
After your explanation, it's obvious. It was the lighting in the kitchen. So, if you have your typical indoor, tungsten-lit environment and you expose to the right, chances are you could have a clipped red channel? In which case, you'd have to expose not so far right to get the red channel within the boundaries of the histogram? Is that assessment accurate?

Right, it's the red component of the 'white' light; no need for a red object. In fact, having a properly exposed red object shouldn't blow out the red channel because it'll be represented on the histogram as magnitude, not brightness. The camera can deal with an all-red scene; it just records a lot of red.

And yes, you'd have to expose not-so-far-to-the-right. And that is why people are advocating using gray card; you won't be anywhere near the right.

I am by no means an expert in this but I can occasionally explain something well. Glad it worked for you!