In darker environments, face detection using the rear camera can be unclear due to the focusing mechanism in Xiaomi smartphones. They rely on phase detection autofocus, which requires sufficient light to accurately detect phase differences for proper focusing. When the lighting is insufficient, the autofocus system will struggle to detect the correct phase difference for faces and instead focus on other brighter points in the scene.
This is a common issue with mainstream smartphones in low-light conditions. To improve focus accuracy, try adjusting your angle or adding some light to illuminate the face when taking photos in very dim environments. This will help ensure that the focus is accurately locked onto the subject’s face.