You should read Jue Wang's 2007 survey paper which groups and puts all the techniques in context, then a handful of the top performing papers from recent years

You should read Jue Wang's 2007 survey paper which groups and puts all the techniques in context, then a handful of the top performing papers from recent years on alphamatting.com http://www.juew.org/publication/mattingSurvey.pdf http://www.juew.org/publication/mattingSurvey.pdf