Canon PowerShot SD900 Digital Elph User Manual page 59

You are recommended to set the shooting mode to
and the exposure compensation setting to [±0]
before setting a custom white balance.
The correct white balance may not be obtained
when the exposure setting is incorrect (image
appears completely black or white).
Shoot with the same settings as when reading the
white balance data. If the settings differ, the optimal
white balance may not be set.
In particular, the following should not be changed.
- ISO Speed
- Flash
Setting the flash to on or off is recommended. If
the flash fires when reading the white balance
data with the flash set to
that you also use the flash when you shoot.
Since the white balance data cannot be read in
Stitch Assist mode, preset the white balance in
another shooting mode beforehand.
(Auto), make sure
57