  We address an essential problem in computer vision, that of unsupervised
object segmentation in video, where a main object of interest in a video
sequence should be automatically separated from its background. An efficient
solution to this task would enable large-scale video interpretation at a high
semantic level in the absence of the costly manually labeled ground truth. We
propose an efficient unsupervised method for generating foreground object
soft-segmentation masks based on automatic selection and learning from highly
probable positive features. We show that such features can be selected
efficiently by taking into consideration the spatio-temporal, appearance and
motion consistency of the object during the whole observed sequence. We also
emphasize the role of the contrasting properties between the foreground object
and its background. Our model is created in two stages: we start from pixel
level analysis, on top of which we add a regression model trained on a
descriptor that considers information over groups of pixels and is both
discriminative and invariant to many changes that the object undergoes
throughout the video. We also present theoretical properties of our
unsupervised learning method, that under some mild constraints is guaranteed to
learn a correct discriminative classifier even in the unsupervised case. Our
method achieves competitive and even state of the art results on the
challenging Youtube-Objects and SegTrack datasets, while being at least one
order of magnitude faster than the competition. We believe that the competitive
performance of our method in practice, along with its theoretical properties,
constitute an important step towards solving unsupervised discovery in video.
