18% Gray / Custom White Balance ...

[Digital Prophet]

Ok, I'm just a moron. But frankly I am not entirely sure which to use on my Digital Rebel.

Some places I read people saying to take a picture of a white surface and use it as the "Custom White Balance". Other places have people saying to "... find something that is 18% gray to set the in camera meter". But that is kind of misleading to a newbie like me b/c we don't know that "18% gray" doesn't refer to an object that is "18% gray" but rather a "gray surface that reflects 18% of the light hitting it". That is kind of an important distinction.

So I went and got a "gray" card and I got a piece of 108 white paper and taped it to a board. I have been trying them both out inside and out but I just don't quite seem to be getting it right. It just seems to me that one method should work better than the other. But I seem to be gettting varied results.

The reason I have been so hot on this is that I have a semi-formal opportunity to have a shoot with a large group of people and several jets. And since this setup will take a bit of work I want to do everything I can to make sure that I get a good exposure. But it seems to me that the varying tones of "white" on the jets always seems to be tossing my exposure off. They almost always come out over exposed. I have even considered used a graduated nuetral density filter to help with this issue since the people will be in foreground of the jets.

Any ideas, thoughts or mystical encantations on this matter would be very educational to a newbie like me.

Digital Prophet

[hmhm]

Custom white balance requires a "subject" of neutral reflectivity with respect to color. This means that the amount of visible light reflected by the object doesn't differ significantly for different colors. Either a grey object or a white object can have this property, the white object will simply reflect a greater amount of light than the grey one. From the camera's perspective, a grey card in bright light and a white card in dimmer light are indistinguishable.

Now, this all assumes that the white card and grey card are both equally neutral. If your "white card" is really a white sheet of paper, well, different types of white paper do have different "tints".

From a white balance perspective, it doesn't matter that the grey card is "18% reflective", this calibration has value for exposure metering.

In-camera "reflective" metering requires subjects of 'average reflectivity'. If your subject is very bright (i.e. white planes), it's easy for the camera to be fooled into underexposing the shot. If there's a bright background (i.e. white planes) and a darker foreground (i.e. people in tuxedos), then the camera might easily choose an exposure that either "blows out" the white background or else underexposes the black foreground, losing detail in either case.

You can "fix" the problem of fooling the camera's metering by using a handheld incident meter, or else by using an 18% grey card and in-camera metering to measure the exposure, record the values, and apply them to M mode exposures. For digital, though, and some "set-up" shots, your best bet is probably to just do some trial and error until you get an exposure that works right. You can do some of this experimentation before your real subjects get in front of the camera so you're not wasting their time.

There's not much you can do to increase the range of bright and dark values that your digital camera can capture (though a film camera with negative film will do better in this case). The best you can do is to expose carefully, monitor the histogram and preview images, and reduce the exposure using exposure compensation (or adjusting shutter speed or aperture in M mode) until you stop blowing out the highlights. Shoot in RAW, and post-process the images to try to draw out as much detail as you can in the shadows.
-harry

[CanonUser]

You are confusing 2 separate subjects here. The first is to set the white balance, or telling the camera what the correct white color of an object for the given lighting situation. For example, you take a photo of a white photo paper in the light of a sunset. Next you set the custom WB using this photo. The camera will substract the extra yellow cast off this photo to render the paper a neutral white. Then it applies this setting to all subsequent photo that you'll take.
The next issue is to set the proper exposure. In the old day, the gray card is used to meter a lighting situation. With digital camera, learn to use the histogram in conjunction with the various metering mode available. Underexpose a little bit to protect the hilights. You have a better chance of getting a great picture than using the gray card.
For the best result, shoot RAW. Meter the scene as best as you can with the histogram. Include the photo paper and the gray card in the frame of the first few shots. Then set up the group abd shoot away. Open the RAW files in Capture1 software, use the eye dropper tool to get the perfect WB and exposure, along with a few other settings.

Regrads,
Alan

[scottbergerphoto]

It doesn't matter whether you use an 18% Grey card or a White card. Both will work. It is important that the card be properly exposed to get an accurate white balance. Using an 18 % Grey card makes this easier because if it's properly exposed you will get a peak in the center of the histogram. If the shot is overexposed or underexposed you may not get a proper White Balance. This is straight out of the Canon Manual (1D Mark II). So you actually have to do 2 things in setting a Custom White Balance. You need a proper exposure and an 18%Grey Card or something White.
Regards,
Scott

[hmhm]

It is important that the card be properly exposed to get an accurate white balance. Using an 18 % Grey card makes this easier because if it's properly exposed you will get a peak in the center of the histogram.

Well, if you use in-camera metering, and don't try to influence it with exposure compensation, the camera should render either a white card or a grey card as equally grey.
-harry

[scottbergerphoto]

It is important that the card be properly exposed to get an accurate white balance. Using an 18 % Grey card makes this easier because if it's properly exposed you will get a peak in the center of the histogram.

Well, if you use in-camera metering, and don't try to influence it with exposure compensation, the camera should render either a white card or a grey card as equally grey.
-harry
That's true, but the White Card would not be properly exposed.It would be underexposed. For the white card to be properly exposed you would have to add 1-2 stops exposure so it looks white. That's anonther reason it's easier with a grey card.
Scott

[skimmel]

I recently went to purchase a neutral grey card to custom WB my 10D. They had at Calumet a "digital grey card" that is apparently 11% neutral grey (or somewhere around that). Does anyone no if this is any better than a standard 18% grey? The rationale was that there was something unique about digital and WB that makes the digital grey card better. Is this just hype? Thanks.

[Roger_Cavanagh]

I recently went to purchase a neutral grey card to custom WB my 10D. They had at Calumet a "digital grey card" that is apparently 11% neutral grey (or somewhere around that). Does anyone no if this is any better than a standard 18% grey? The rationale was that there was something unique about digital and WB that makes the digital grey card better. Is this just hype? Thanks.

11% gray is closer to real life scene reflectance. Kodak currently advise that you should open up half a stop after taking a 18% gray card reading.

More info here (http://www.rogercavanagh.com/helpinfo/29_graycard.htm).

Regards,

[hmhm]

That's true, but the White Card would not be properly exposed.It would be underexposed. For the white card to be properly exposed you would have to add 1-2 stops exposure so it looks white. That's anonther reason it's easier with a grey card.
Scott

This is important if your goal is to take a nice portrait of the white card, which the white card could frame and give to his grandparents. If your goal is to use the card for white-balance, then you certainly do not need an image that looks like the white card does in real life, you just need an image that captures the light that reflects off the white card, to sample the color of this light is our only goal.
-harry

[hmhm]

I recently went to purchase a neutral grey card to custom WB my 10D. They had at Calumet a "digital grey card" that is apparently 11% neutral grey (or somewhere around that). Does anyone no if this is any better than a standard 18% grey? The rationale was that there was something unique about digital and WB that makes the digital grey card better. Is this just hype? Thanks.

The standard grey card is 18% grey, but most in-camera meters actually assume that the standard "scene" has about 12% (or so) reflectivity. When using a grey card for doing exposure metering, you want the card's reflectivity to match that of the expected reflectivity built-in to the camera's metering system. If you use a standard 18% grey-card, you have to take the in-camera meter's reading and add about a half-stop of exposure to that to compensate for the difference. This adjustment shouldn't be necessary with an 11% grey card, which is about the reflectivity that the camera's metering assumes.

I think the "designed for digital" claim is really a "we're really, really neutral, so we're really, really good for white balance", though technically any grey card should have this property, and white-balance is an issue in film photography as well.
-harry

[scottbergerphoto]

Error

[scottbergerphoto]

That's true, but the White Card would not be properly exposed.It would be underexposed. For the white card to be properly exposed you would have to add 1-2 stops exposure so it looks white. That's anonther reason it's easier with a grey card.
Scott

This is important if your goal is to take a nice portrait of the white card, which the white card could frame and give to his grandparents. If your goal is to use the card for white-balance, then you certainly do not need an image that looks like the white card does in real life, you just need an image that captures the light that reflects off the white card, to sample the color of this light is our only goal.
-harry
I can only tell you what I've read in the Canon Manual and this Tutorial at : http://www.luminous-landscape.com/tutorials/dig-exp.shtml
The author seems to feel making that white card suitable for framing is important to an accurate white balance. If you notice, the histogram and the picture, show the white card as white, not grey and not in the middle of the histogram.
Scott

[dn7elson]

Has anyone used the Perfect Picture Card?

There would seem to be some advantage in having a white reference point, grey as well as black in the image, particularly for post processing setup.

http://www.imageguy.com/PPC_1.php

Being small and plastic it would be easily useable in the field.

Am I missing something? (Another topic that I am trying to learn :) )

[skimmel]

The standard grey card is 18% grey, but most in-camera meters actually assume that the standard "scene" has about 12% (or so) reflectivity. When using a grey card for doing exposure metering, you want the card's reflectivity to match that of the expected reflectivity built-in to the camera's metering system. If you use a standard 18% grey-card, you have to take the in-camera meter's reading and add about a half-stop of exposure to that to compensate for the difference. This adjustment shouldn't be necessary with an 11% grey card, which is about the reflectivity that the camera's metering assumes.

Thanks Harry. So, this seems that 11% grey may be most beneficial for setting exposure (ie. not having to add 1/2 stop of exposure) but no better for setting custom WB than a white card or 18% grey. Am I understanding correctly?

[caldgrp]

That's true, but the White Card would not be properly exposed.It would be underexposed. For the white card to be properly exposed you would have to add 1-2 stops exposure so it looks white. That's anonther reason it's easier with a grey card.
Scott

This is important if your goal is to take a nice portrait of the white card, which the white card could frame and give to his grandparents. If your goal is to use the card for white-balance, then you certainly do not need an image that looks like the white card does in real life, you just need an image that captures the light that reflects off the white card, to sample the color of this light is our only goal.
-harry
I can only tell you what I've read in the Canon Manual and this Tutorial at : http://www.luminous-landscape.com/tutorials/dig-exp.shtml
The author seems to feel making that white card suitable for framing is important to an accurate white balance. If you notice, the histogram and the picture, show the white card as white, not grey and not in the middle of the histogram.
Scott

The 10D Manual, p 52, says "shoot the white object so that a standard exposure is obtained" I interperted that statement to mean the histogram peak of the white object should be in the middle, not that the image in the LCD monitor should be white. It seems to work. While the reference white object will show, say, an orange cast, that orange hue is gone in the picture taken using that custom white balance. Yet Scott, who is invariably right-on, suggests while I have improved my picture it could be better.

Maybe Canon should define "standard exposure" for a white object.

[scottbergerphoto]

Yet Scott, who is invariably right-on, suggests while I have improved my picture it could be better.


:lol: :lol: :lol: :lol:
Often wrong, Never in doubt,
Scott

[robertwgross]

I don't like to use a gray card for setting white balance. If I use a white card, I can see with my own eyes that it is pure white, or else I could see that it has some color tint to it. With a gray card, I can't tell if it has a tint.

I do use a homemade three-tone target for checking my exposure by histogram.

---Bob Gross---

[maderito]

Without knowing Canon’s logic (and associated algorithm) for custom white balance, all comments are speculative. The manual explanation is certainly open to several interpretations. I’ve not seen a persuasive argument for one point of view vs. another. We’re all left to read between the lines of imprecise manual instructions.

In principle, you need only one neutral value (R=G=B) between black and white to get an accurate white balance – assuming there is only one source of illumination in the image and that its properties are constant across all levels of illumination. Many images have different color temperatures in the shadows vs. the midtones vs. the highlights. That would require a more sophisticated white balance correction than possible using a simple white or gray card.

My guess is that the Canon 10D manual directions for CWB means something like this: expose a neutral flat object to the average illumination of your light source under camera exposure settings representative of your final image. Thus a gray card exposed to appear mid-gray would be my choice. However, if the light were uniform (in temperature) across the image, it wouldn’t matter whether I used a white or gray card. For the white card, I could expose it to appear white or gray, as long as I stayed within the dynamic range of the scene.

For critical work, it is obviously better to do the temperature, white point, and other more refined color corrections in post-processing, preferably using RAW. For situations when you can’t shoot RAW, custom white balance gets you very close to what you want without a lot of post-processing hassle – no mater how you interpret the manual. :)

[Peter_Photo_Guy]

You may want to check out Perfect-Pixs 3 Card Kit. I got it on EBay and use it instead of my gray card. The kit included a gray zone card, a white card and a colour patches card.
Pete

[Jon]

Please note that this is about a 2 year old thread. This has been hashed over repeatedly in the intervening years.

[DavidEB]

an old thread, but nobody has pointed out that the 11% gray card is designed for digital because of the 1.6x crop factor, which makes it the equivalent of an 18% card on full-frame.

let's see if that gets the flames started. Should at least smoke out CDS.

[Mr. Clean]

LOL - It's still really useful information though!

[nadtz]

an old thread, but nobody has pointed out that the 11% gray card is designed for digital because of the 1.6x crop factor, which makes it the equivalent of an 18% card on full-frame.

let's see if that gets the flames started. Should at least smoke out CDS.

Keke. that just made my day.

[Hal Holt]

The idea of using an 11, 12 or 13 percent card in lieu of 18% reflectance was discredited many years ago. Exposure meter equations provide no variable for reflectance. For the purposes of this thread one is really most interested in neutrality.

[NickSimcheck]

My, my, how much more advanced we are now some 2 years later. I wonder, in another 2 years will we be joking about "18% Grey" when we're using our halogram white balance cards.

[corinto]

Some places I read people saying to take a picture of a white surface and use it as the "Custom White Balance". Other places have people saying to "... find something that is 18% gray to set the in camera meter".

There are two issues here: WB and Exposure.

For WB you can use anything that will give a neutral color: white or whatever grade of gray you may find. All that is needed is that it is neutral, meaning equal amounts of Red, Green and Blue. While the advantage of using a 18% gray card is that it is 'calibrated', it does need better light for the camera to 'see' it well. On the other hand, white may be provided by any stationary paper and it is easier for you (provided good enough light) to see if it is pure white (or off-white) without a trace of color. This is rather difficult to observe in gray material.

Be careful that which ever card you use does not pick up color from surrounding surfaces (walls, vegetation, etc.)

For exposure, the gray card is a good thing but it may be replaced by a long list of other resources: histogram, palm of your hand, sky set to +2, etc.

[FlashZebra]

So I went and got a "gray" card and I got a piece of 108 white paper and taped it to a board.
Many (most?) 18% gray cards are white on the flip side.

Enjoy! Lon