HTC One M8 for Windows - Manual (Page 128)

Composition
§ Match your subject with an interesting background. Positioning
your subject with some lights or a garden in the background will
add color and distinction to your photo, especially if you'll use the
UFocus
™ feature in HTC Photo Edit.
§ Post-processing effects for Duo Camera may not work if your
subject and background are too close or when you're taking a
close-up shot. So, mind the distance between your subject and your
background, as well as the distance between the camera and your
subject.
1 m ~ 2 m
128 Camera