Canon EOS Rebel XT - Manual (Page 58)

3 Custom White BalanceN
58
5 Select the custom white balance.
¡ Press the <
S> key to select <
O >,
then press <
0>.
¡ When you press the shutter button
halfway, the <
O > icon will be
displayed on the LCD panel.
¡ If the exposure obtained in step 1 is underexposed or overexposed, a
correct white balance might not be obtained.
¡ If an image was captured while the processing parameter was set to [B/
W] (p.65), it cannot be selected in step 3.
Instead of a white object, an 18% gray card (commercially available) can
produce a more accurate white balance.