A Short Primer on Color Balance for Digital Photography

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How to Use Your DigitalGreyKard: 

     The auto white balance (AWB) feature on most digital cameras works reasonably well in many conditions, but it works very poorly in others - especially under artificial light sources such as incandescent and fluorescent light. Most  digital SLRs have various pre-programmed white balance modes (such as flash, sun, shade ...), but they are just approximations of the actual color of the light. You will find that your photos will have strong color casts under certain conditions.   For example, on AWB my Canon DSLR's render indoor tungsten lighting with a noticeable orange cast, and if the tungsten lights are stage or convention hall flood lamps, the problem is even worse.  These are the best times to use a DigitalGreyKard. 
   
The DigitalGreyKard takes reflected light into consideration. The camera and the computer can be "told" that the light reflected from the card is spectrally neutral.  Once the camera or software have such a reference, they -  make adjustments to all the colors in the scene using a custom white balance . I find my white balance results to be excellent when using the DigitalGreyKard.  
   
To use a DigitalGreyKard, simply take a picture of it in the same lighting your subject is (or was) in. Use auto white balance and P (Program) mode for the picture. You can either use the resulting picture as the basis for a custom white balance setting, or you can use the DigitalGreyKard picture during post processing for a custom white balance. The glossy surface of the DigitalGreyKard will instantly reveal any reflections that may lead to incorrect white balance.  If reflections are seen on the DigitalGreyKard surface during a white balance operation, reposition the DigitalGreyKard so that reflections are eliminated. 

How to Use Your DigitalGreyKard for In-Camera Custom White Balance: 

To use the DigitalGreyKard as the basis for an in-camera custom white balance, make sure enough of the center of the frame is covered by the card in your picture to be properly read for white balance. This works for JPEG shooters.  If I'm using my DigitalGreyKard, I fill the frame with the  grey or white of the card. Next, go through the menu to select that picture for your custom white balance. Finally, set the camera to the custom white balance setting. 

Remember, you will need to shoot a new custom white balance shot each time you go into a different room, or the sun goes under a cloud, or if you are pointing your camera at a portion of the scene that is more strongly lit by one particular light source. This can get tedious, since light can be so variable.  Custom white balance works well in the studio, but in many shooting situations it will not be practical.  

How to Use Your DigitalGreyKard for Post-Processing: 

If you are using the DigitalGreyKard picture as the basis for your post processing white balance setting, the card does not have to take up much of the frame and does not need to be exactly centered. This applies to shooting RAW files. 

When shooting a wedding, for example, the idea is to walk through the location and shoot a photo of the grey card in each room of the house, each location in the church, or each place at the reception where you expect to shoot the wedding party later.  You simply hold the grey card out in front of yourself where it is lit by the same light as the area of interest and take a shot of the card and its surroundings.  Use a wide angle lens so you can see where you were when you made the shot. Once you complete the shoot, you go back to your grey card images and use the appropriate image to set white balance for each series of shots.

To use the grey card in your post-procession workflow, simply select a point in the DigitalGreyKard picture in your post processing software to be the basis for the custom white balance setting. Then select the images taken under that lighting and tell the software to set the white point for all of them.  Many pros prefer to use this technique.  This feature is built into many post-processing software such as Capture One Pro, Lightroom, Aperture, and others.  

How to Re-Use White Balance Information from Your DigitalGreyKard: 

DigitalGreyKard pictures can be saved for later use as well. If you take pictures in the same lighting at different times, you can use an old DigitalGreyKard shot for future photo sessions. For example, keep a DigitalGreyKard shot of your kitchen or living room to use each time your inlaws come over. Keep a shot of your high school gymnasium to use each time your kid's team is playing there.

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