White card/gray card WHAT???

I have not used a * card in my photography experiences.
What is the benifit? In what situation should I use this procedure?
How is it done?

There are two general ways to use a card for setting white balance with the in-camera metering system.
1. Place the card in a shot somewhere. Later, in PhotoShop, you can select this with the gray eyedropper tool to let it know this should be neutral gray.
2. When you want to adjust WB in-camera for specific lighting conditions, you can take a shot of the gray card (or white card) under those lighting conditions. Make sure the card takes up at least the center 1/3 of the image. Go to the menu on the camera, scroll down to white balance, select "Custom White Balance". You will be prompted to select the photo to use. Select the one you took of the gray card. You have now "registered" that shot, under those lighting conditions as your "custom white balance" settings. On the camera, press the white balance button, and scroll to the icon that represents "Custom" (instead of AWB).
All this does it to tell the camera that this is a gray object, so it should adjust it's color temperature to make it gray.

White and gray cards are used for two different things.

White and light gray cards are used to set your custom white balance setting on your digital camera. They are also used in reference shots so that you can tweak white balance later during image processing.

Photo Gray cards are used for exposure. 18% gray cards were once considered the stardard however with digital more and more photographers are starting to use other cards that have closer to 12% gray or have graduated gray scales.

The bottom line to all this is....if you want control over the image creation and image post processing process....both cards are useful additions to your photo kit and worth the time to learn how to use them.

If you are really into it you also want to check our the color reference cards too.

[QUOTE=SWPhotoImaging]
1. Place the card in a shot somewhere. Later, in PhotoShop, you can select this with the gray eyedropper tool to let it know this should be neutral gray.
quote]

I have several questions regarding this:
- What values do you regularly use for the neutral gray, the lights and the shadows? (the 3 eyedroppers)
- If I'm shooting several pics, how can I make them all have the same neutral gray. In the one with the card, you slect the card with tha eyedropper. What about the others?
Thank you in advance

Gray Card…White Paper. What’s best?

Need an exposure crutch?

From "Understanding Exposure"; ..."Use your palm instead of a grey card. No matter what lighitng conditions you do this under, your palm will consistently read about +2/3 to 1 stop overexposed from reading of a gray card."
Of course if you want to know more...I suggest reading the book. ; )

The "must read" for gray card use:

http://www.acecam.com/​magazine/gray-card.html

Also, RawWorkflow have good docs about the use of your gray card (WhiBal):

http://www.rawworkflow​.com/

Alex

Great links, Alex!