At a New York gallery in 1980, the artist Alice Neel unveiled a portrait of herself holding a paintbrush and sitting in front of a canvas while completely nude. Neel’s brave and unflinching self-portrait as a 80-year-old woman stripped to her essence reflects the direct and unsentimental way she painted the scores of people who sat before her easel over the decades: unvarnished, sometimes raw, yet always fully human. The painting is one of more than 100 works spanning the arc of Neel’s career in “Alice Neel: People Come First,” a major retrospective on view through July 10 at the de Young Museum in San Francisco.