Custom White Balance: White or Gray Card

[photos4fun]

Excuse the simple question, but it seems from my manual (Nikon D7000) I can use either a white card or a gray card (18%?) as a source for a custom while balance. Three questions:
1. How is it that I can use either color?

2. Is there an advanatage to one over the other?

3. I have an ExpoDisc but when I use it, the colors seem fairly warm. Is there a way to "coll" that down?

Thanks!!

[Narsuitus]

I cannot explain how the camera is able to obtain the proper white balance from either a gray card or white card. All I can say is that it works.

In fact, I have tried the following white balancing tools and all have been acceptable.

1.Gray card
2.White card
3.White paper plate
4.White notebook paper
5.White coffee filter
6.White tracing paper
7.White balance lens cap
8.Expodisc

Some have just been more acceptable than others. For example, my Expodisc produces accurate results more consistently than any of the others. My gray card produces inaccurate results more than any of the others.

Unless you are using a Warming Expodisc instead of the regular Expodisc, I am surprised you are getting images that are too warm.

http://www.flickr.com/photos/11336821@N00/7375697286/

[kgphoto]

It is important to not overexpose the target past white, or there will be no info for the camera's algorithm to work with. So a Gray card provides a bit of margin for error. The real important aspect is that the target be totally neutral. Most gray cards aren't made to tight color specifications, just reflective specifications.

If the target or device isn't totally neutral it can create a color cast rather than a neutral result. So try a Whi-Bal for a true neutral. Some people find it too cool since they are used to seeing warm results from the bluing in the white objects they use.

[Sailor Blue]

White Balance Filters Product Comparison: (Professional Photographer Magazine Web Exclusives)

Personally, I use two methods.

First and foremost I use a Datacolor ColorChecker Passport to not only set a white balance but to correct any color casts caused by lighting and/or my camera sensor and lenses. I know that this will give me a color correction I can apply to all the shots taken in the same lighting so that I will get absolutely neutral color images. I can then apply any tinting I want to achieve a more pleasing result.

For quick and dirty WB I use a sheet of white acrylic plastic I bought at an art store. I sanded it down to make the surface dull so that direct reflections are minimized. It is practically indestructible and if it gets dirty I can just wash it or sand it down again. From one $3 12" square sheet I made one 8.25"x12" sheets for studio use and two 3.75"x6" sheets for travel.

Whether you use a white or a gray card makes no difference to WB, the camera will see it as gray whether it is black, gray , or white. All that is important is that it is neutral in color - I checked by white plastic sheet against my Passport before deciding it was acceptable.

[kgphoto]

The whole idea is for a target to return equal values in RGB. As long as you don't go to 255,255,255 so there is no info to work with, anything will work. The problem is finding something that is truly neutral. The other thing is to insure it won't floresce with ultra violet or UV light.





The other advantage of the WhipBal is the black and white points provided. The contrast target makes the auto focus on your camera work while setting a custom white balance. While it is also matte to avoid reflections, its black patch is highly reflective to help you see when you have glare on the card. Glare can change your white balance reading.



Finally, reasonable cost so you don't have to go out find and test targets, spend time sanding it and so forth.

It is also available in many sizes to make it convenient to have on hand and to use.

[photos4fun]

Thank you all for the responses. I have a Lostolite collapsable 18% gray card with a bullseye on it. I "sometimes" remember to take a test shot with it to help with color correction in post, but now I suppose I can use it to set a custom white balance as well. I "think" the other side of the card is white. I'll make some test to see how they may be different.

I guess the eternal challenge is when there are many different color temperatures in the same shot.

Thanks again.

[kgphoto]

I tried that device and found it wasn't neutral, at least the one I had. Also as a fabric device it can get dirty or stained and tear. I have another model and the spring steel is ripping out of the seam. So for $60-$100 I prefer something that lasts longer and can be cleaned. You can drop the plexi or the Whi-Bal in the mud and just wipe it off, or wash it later and it is good as new.

[kgphoto]

I should also mention that dead neutral may not be necessary for many people and many shots. It is easier to start with dead neutral before you add your taste adjustments to speed up the process and increase the consistency of your look.

If you are shooting advertising it then becomes critical that the colors are accurate.

[deluco]

With my camera system, white gives truer colors. Some camera's may vary. Also, in some circumstances you may want a warmer or cooler tone.

[kgphoto]

And of course all of this is a moot point of you don't regularly calibrate your monitor.