Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 873)

: One-Touch Image Quality (Hold)
Pressing the button assigned to this function enables you to switch to the image size set
here. While the camera switches the image size,
icons blink in the viewfinder and
the image size blinks on the rear LCD panel. One-touch image quality setting is not
canceled after you shoot. To return to the original image size, press the button assigned to
this function again.
* 7: To set the image size for this function, press the < > button when the setting screen is
displayed.
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