Canon imageCLASS MF4690 Operation Manual page 185

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Press [ ] or [
USB Memory (B&W): <200X200dpi>, <300X300dpi>, <400X400dpi>, <600X600dpi>, <150X150dpi>,
<200X100dpi>
USB Memory (Color): <200X200dpi>, <300X300dpi>, <100X100dpi>, <150X150dpi>
If you have selected <PDF (COMPACT)> as the file format in step 5, only <300X300dpi> can be selected
for sending color images attached to an e-mail message.
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] to select the resolution, then press [OK].