Canon EOS REBEL T8i Advanced User's Manual page 294

4.
Select [
5.
Select [
Caution
If the exposure obtained in step 1 differs greatly from the standard exposure, a
correct white balance may not be obtained.
These images cannot be selected: Images captured with Picture Style set to
[Monochrome], images with a Creative filter applied before or after shooting,
cropped images, or images shot with another camera.
Images that cannot be used in the setting may be displayed.
Note
Instead of shooting a white object, you can also shoot a gray chart or standard 18%
gray reflector (commercially available).
: White balance].
].
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