Canon POWERSHOT S100 User Manual page 94

You can change the AF (Auto Focus) frame mode to match the scene you
want to shoot.
Choose'0'.
After pressing the @ button, press the
,_v buttons to choose ,_,.
Choose an option.
Press the _t I_ buttons or turn the _ dial to
choose an option, then press the @
button.
The option you set will appear on the
screen.
_ Face AiAF
Detects people's faces and sets the focus, exposure (evaluative metering
only) and white balance (AWBonly).
When the camera is pointed at subjects, a white frame appears on the face
the camera judges to be the main subject, and gray frames (max. 2) will
appear on other faces.
A frame will follow a moving subject within a certain range.
When the shutter button is pressed halfway, up to 9 green frames will
appear on faces that the camera focuses on.
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