HTC One M8 User Manual page 117

Lighting
Use Duo Camera in an environment where there is a good light
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source. Post-processing effects for Duo Camera do not work for
low light photography or when you're using the camera flash.
If lighting is uneven, like when the background is a little bit under or
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overexposed, tap
Hold HTC One so that you don't block the second camera lens.
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Composition
Match your subject with an interesting background. Positioning
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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 ™
to adjust the exposure settings.
feature in Gallery.
Camera 117