1. A method comprising: obtaining a first frame of color pixel data; checking whether a reset flag is cleared or set at a first time; generating a trimap for the first frame, wherein: if the reset flag is cleared at the first time, then generating the trimap for the first frame comprises: obtaining a user-extraction contour that is based on an immediately preceding frame; and generating the trimap for the first frame based on the obtained user-extraction contour; if the reset flag is set at the first time, then generating the trimap for the first frame comprises: detecting at least one persona feature in the first frame; generating an alpha mask at least in part by aligning an intermediate persona contour with the detected at least one persona feature, wherein the intermediate persona contour is based on a result of a color-based flood-fill operation having been performed on a previous frame of color pixel data that had been segmented by a machine-learning-segmentation (MLS) process; and generating the trimap for the first frame based on the generated alpha mask; and outputting the generated trimap for use in extracting a user persona from the first frame.