We recommend that users do a CUSTOM gray/white balance, "pre-process," in 
their camera right before taking pictures in any given scene/lighting 
condition. This is the best, most accurate and efficient way to use this 
tool. We realize that is not always possible with certain cameras or when 
time doesn't allow. If that is the case, then you can still do it in "post 
process" in the computer by photographing one frame with the Expo/Disc at 
any time in that particular lighting condition. You can set your camera to 
"auto exposure" for this, but NOT auto white balance.

To enable the post process correction later on in Photoshop, you must 
first "get it close" by using a PRESET manual color balance to match the 
dominant light source in the scene. In sunny conditions, use daylight, in 
overcast conditions, use the cloudy setting, indoors at night, use the 
"incandescent setting." Under fluorescent, use the fluorescent setting. 
Keep in mind that no device can correct a gross color error (like using 
flash on an "incandescent setting" -- the images will be way too blue). 
You can do an acceptable correction job, but it certainly will be far from 
perfect. Good color in your prints does take a little work, lots of 
practice, and the development of good habits.

For post process color correction in Photoshop with any file format (TIF, 
Jepeg, or PSD), your computer monitor should be calibrated first, so the 
colors you see on the monitor will be more accurate, but it's not the most 
important issue. Neutralizing the color cast for your prints IS the most 
important issue. The printed images will never have colors identical to 
what you see on a glowing monitor because prints are reflective and 
monitors are emissive, by nature. However, you can come very close when 
you do everything right.

1. Open the camera-generated Expo/Disc gray frame image (shot in the same 
lighting as the image you want to correct) in Photoshop.

2. Open the image you want to correct at the same time and make sure it is 
the current window.

3. Hit “CONTROL” or “ Command L” on the keyboard. This will bring up the 
Levels/histogram display in Photoshop along with 3 eyedropper buttons.

Use the medium (gray) eyedropper to click anywhere on the Expo Disc gray 
frame image to apply that gray balance to the image you want to color 
correct. You can correct the rest of the images the same way, or you can 
save the curve and re-apply as required.

You can also record an action to apply a batch process to the rest of the 
images photographed in the same light, or process one image at a time by 
pushing a function key. Since the ExpoDisc can produce perfect R128, G128, 
B128 image when gray balanced in Photoshop (provided the camera is 
designed and set up to create that exact exposure), this provides the 
basis for correcting color casts, which exist in every scene. It will even 
correct for slight color shifts with studio lighting (different aged 
flashtubes, UV coatings, aged light modifiers, etc.) in one simple reading 
and "click balance."

5. You can apply the same balanced gray frame to all images captured in 
the same lighting conditions. Shoot a new Expo/Disc gray frame whenever 
the lighting changes—they will also serve as index markers to separate 
batches according to their lighting conditions. You can change the Gray 
Balance for creative purposes by trying out different grayframes later on.

Diane Wallace
Wallace Photo Products
www.expodisc.com
1-800/446-5086