Canon EOS 100D Basic Instruction Manual page 259

If the exposure obtained in step 1 differs greatly from the standard
exposure, a correct white balance may not be obtained.
In step 3, the following images cannot be selected: images captured
while the Picture Style was set to [Monochrome] (p.101), images
processed with a Crea ive filter, and cropped images.
Instead of a white object, a gray chart or 18% gray reflector
(commercially available) can produce a more accurate white balance.
The personal white balance registered with EOS Utility (provided
software, p.366) will be registered under <O>. If you perform step 3,
the data for the registered personal white balance will be erased.
Select [Custom White Balance].
2
Under the [z2] tab, select [Custom
White Balance], then press <0>.
The custom white balance selection
screen will appear.
Import the white balance data.
3
Select the image that was captured in
step 1, then press <0>.
On the dialog screen that appears,
select [OK] and the data will be
imported.
When the menu reappears, press the
<M> button to exit the menu.
Select [O (Custom)].
4
Under the [z2] tab, select [White
balance], then press <0>.
Select [O (Custom)], then press
<0>.
3 Matching the Light SourceN
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