18% Grey Card: WB or EC?

Grey card should be used to correctly set the exposure or white balance?

My first experience with grey cards was when I was taking a b&w film photo class. My impression since then has been that it's used to correctly set the balance between light and dark areas. Since 18% grey is the most common shade, setting the camera to correctly expose it will produce a correct balance between bright and dark areas. All that makes sense.

But how does it relate to White Balance?

My understanding of WB is that the temperature of light (and not exposure) will dictate the overall white balance. So how can the gray card be used to calibrate for WB?

I was just thinking about the same thing, I'm currently taking a B&W film class as well.

I think your 5D mark II should correct everything!

bump for a response

WB can be achieved on anything that lacks saturation. Grey Card, White Paper, Black Muslin...

Doesn't matter so long as all three values of RGB are the same.
255, 255, 255
100, 100, 100
0, 0, 0

Will all give correct WB

If all 3 will work for WB, then why do cards such as WhiBal have BOTH grey & white sides to them? This has also been a source of some confusion for me. I mean, I go to shoot an indoors event, set to AWB, and snap a picture of both White & Grey sides of my card ... just so I have them both as a reference point in PP ... (shooting RAW).

Cody21 wrote in post #5523406
If all 3 will work for WB, then why do cards such as WhiBal have BOTH grey & white sides to them? This has also been a source of some confusion for me. I mean, I go to shoot an indoors event, set to AWB, and snap a picture of both White & Grey sides of my card ... just so I have them both as a reference point in PP ... (shooting RAW).

Probably because most folks just think White Balance comes from White but it doesn't have to.

The white side can be handy to double check where your clipping level is though. If your histogram looks a little shoved to the right but the white card isn't blinking, you're not blowing your highlights. I like the WhiBal because it give me a White Point, Grey Point and Black Point all on one handy little gadget.

So let me understand this. When you're shooting in bright light (full sun?) situations, you snap a shot of the White side and adjust your meter so that the white in the card is not "blown out" ? I had always been using the Grey side in bright light, the White side when indoors... hmmm...

Cody21 wrote in post #5523508
So let me understand this. When you're shooting in bright light (full sun?) situations, you snap a shot of the White side and adjust your meter so that the white in the card is not "blown out" ? I had always been using the Grey side in bright light, the White side when indoors... hmmm...

You have two finite ends of the exposure scale: 0 and 255.

There's no more shadow information available below zero and no more highlight information once you hit 255. There's no such thing as the photographic equivalent of turning the volume up to "11"

However, what's your critical element in the shot? If it's someone's face and you have to blow some highlights to get a good exposure for their skin, then you don't have much choice but to blow some highlights.

It also depends (I think) on the criticallity of your work. Some situations allow you to get away with clipping some whites or blacks and some don't. Look at the big commerical fashion or swimwear shoots. Scrims, reflectors, flags, white cards, black cards and 101 other ways to keep the light between 0 and 255 simply because the client is paying for every pixel and lost information is unacceptable.

Same with critical shoots where they rely on a GretagMacBeth "Color Checker." They don't use them because they want to make sure red is red and blue is blue. They use them because the "Red" they require has to be exactly 237, 28, 36 and not simply 255, 0, 0.

It's a matter of degrees... Most of us want to acheive photos that "look right." However there are situations where nothing short of absolutely correct is acceptable.

Cody21 wrote in post #5523406
If all 3 will work for WB, then why do cards such as WhiBal have BOTH grey & white sides to them? This has also been a source of some confusion for me. I mean, I go to shoot an indoors event, set to AWB, and snap a picture of both White & Grey sides of my card ... just so I have them both as a reference point in PP ... (shooting RAW).

The Whibal is spectrally neutral, and is grey on both sides. The White/black sticker is there because it allows you to easily detect light conditions which would mess up your reading. If you see a glare on the sticker portion, then you need to angle the card until the glare goes away.

The most important thing is that the object used for reference, when setting WB needs to be spectrally neutral. That allows you to correct for blue/yellow color in light, as well as for any green/magenta tint.

FlyingPhotog wrote in post #5523673
You have two finite ends of the exposure scale: 0 and 255.

There's no more shadow information available below zero and no more highlight information once you hit 255. There's no such thing as the photographic equivalent of turning the volume up to "11"

However, what's your critical element in the shot? If it's someone's face and you have to blow some highlights to get a good exposure for their skin, then you don't have much choice but to blow some highlights.

It also depends (I think) on the criticallity of your work. Some situations allow you to get away with clipping some whites or blacks and some don't. Look at the big commerical fashion or swimwear shoots. Scrims, reflectors, flags, white cards, black cards and 101 other ways to keep the light between 0 and 255 simply because the client is paying for every pixel and lost information is unacceptable.

It's simply a matter of degrees of "correct." Most of us simply want the photo to look right. Some situations require it to be perfect.

Same with critical shoots where they rely on a GretagMacBeth "Color Checker." They don't use them because they want to make sure red is red and blue is blue. They use them because the "Red" they require has to be exactly 237, 28, 36 and not simply 255, 0, 0.

It's a matter of degrees... Most of us want to acheive photos that "look right." However there are situations where nothing short of absolutely correct is acceptable.

Thanks FlyingPhotog,
This is a very simple and to the point explanation about getting the correct exposure. Achieving the perfect balance between shadows and highlights. This information once understood can really improve the quality of pictures as far as the correct exposure is concerned.

Now that I think about it more, I start to realize that maybe saying that the 18% gray card can be used to set white balance is not correct. White balance (at least in my XT and 40D) relates to compensating for different light temperatures. And I don't think it has anything to do with controlling the balance between shadows and highlights but rather it depends on the type of light that is available to light the subject.

The balance between shadows and highlights can be achieved by using the gray card and setting correct aperture/shutter speed - that's not White Balance.

White Balance (at least in my cameras) controls the "temperature" of light in the picture which cannot be controlled in any other way but only by using either lens filters or preset white balance (flash, tungsten etc).

So please correct me if I'm wrong but gray card and white balance don't mix.

The Whibal cards have the white and black stickers on them so that they can be used to quickly set white and black points in post processing. The gray card can be used to not only set a custom WB but also to set base exposure.

Discovery - gray card and WB absolutely DO mix.

The camera doesn't care WHAT 'color' the card is... only that it is BALANCED (ie, Red=Blue=Green). You can use anything from pure white (255,255,255) to pure black (0,0,0) and anything in between... as long as the colors are balanced.

Discov3ry wrote in post #5523854
Thanks FlyingPhotog,
This is a very simple and to the point explanation about getting the correct exposure. Achieving the perfect balance between shadows and highlights. This information once understood can really improve the quality of pictures as far as the correct exposure is concerned.

Now that I think about it more, I start to realize that maybe saying that the 18% gray card can be used to set white balance is not correct. White balance (at least in my XT and 40D) relates to compensating for different light temperatures. And I don't think it has anything to do with controlling the balance between shadows and highlights but rather it depends on the type of light that is available to light the subject.

The balance between shadows and highlights can be achieved by using the gray card and setting correct aperture/shutter speed - that's not White Balance.

White Balance (at least in my cameras) controls the "temperature" of light in the picture which cannot be controlled in any other way but only by using either lens filters or preset white balance (flash, tungsten etc).

So please correct me if I'm wrong but gray card and white balance don't mix.

No, actually, they do...

A good quality grey card is (as Brian mentioned) "spectrally neutral" and can definately be used as a white balance target.

What I was trying to get at is that there are times where you need to divorce the WB aspect of the traditional 18% grey card and its use as an exposure setting device.

There are simply times when relying on an "average" exposure value doesn't work.

I think where things start getting confusing (to me at least) is we talk about Grey Cards being used for WB. I've always believed that a White Card is needed to set a WB in the Camera's Custom WB. Apparently that is not true. And secondly, we talk about using a shot of these cards (White, Black, Grey) as the reference eyedropper for PP. Man, I really struggle trying to keep all this straight.

It took me a little while to wrap my head around it, too. Just try to remember that it is a tool to make sure that white is balanced correctly, and not a white *reference* - that may help.

mnealtx wrote in post #5524223
It took me a little while to wrap my head around it, too. Just try to remember that it is a tool to make sure that white is balanced correctly, and not a white *reference* - that may help.

Ahh..so any reference between white balance (as in balancing white light) using the gray card and White Balance function in the camera (as in getting rid of light temperature tinting) is simply accidental?

I'm not sure I quite understand what you're asking, but let me try.

There IS a connection between using some sort of aid (be it a white card, gray card, black card, expodisc, etc) and setting a white balance for the scene, obviously.

The CWB function in the camera uses one of those aids IN ORDER TO set a white balance, which is a setting to remove any sort of color cast due to the available light. For that reason, whatever aid you use HAS to be color neutral (B=G=R), or it will INTRODUCE a color cast.

Any other WB setting in the camera (AWB, Sunny, Tungsten, etc) is the Canon programmer's 'best guess' as to what a 'proper' WB should be for various scene lighting.

Clear as mud?