WHAT IT’S ABOUT This “American Masters” portrait was produced by Amy Berg, an Oscar nominee for the 2006 documentary “Deliver Us From Evil” about a convicted pedophile, who interviews members of Janis Joplin’s first band, Big Brother and the Holding Company; Kris Kristofferson, whose hit “Me and Bobby McGee” was spectacularly covered by Joplin; record mogul Clive Davis; and famed filmmaker D.A. Pennebaker, whose “Monterey Pop” from 1968 established Joplin.

MY SAY Just to begin at the end, Joplin died at age 27 of a heroin overdose on Oct. 4, 1970. The film certainly doesn’t wrap at that point, because a coda’s needed, or one of those “what did she mean to music” endnotes that tie everything up with a nice (if predictable) bow. But in a smart and surprisingly emotional key change, “Little Girl Blue” does something entirely different: It propels that short life and career across the years, to a moment right now where other lives — and great careers — are still inspired by Joplin’s considerable vitality.

This coda is entirely given over to women — the preceding two hours is almost entirely filtered through the memories of men Joplin had worked with — and it’s quickly apparent they heard something else in those chords, that voice and even her written words. Melissa Etheridge and Pink talk about Joplin’s influence, and so does indie artist Cat Power (Chan Marshall) who covers “A Woman Left Lonely.” Power also plays a part in another effective element in this film as the reader of Joplin’s letters. Joplin often used that quaint, ancient form of human communication as an olive branch extended to disapproving parents back in her hometown of Port Arthur, Texas. “Dear Family, I’m awfully sorry to be such a disappointment to you.”

Power reads passages from these letters that bridge parts of the narrative. They’re oases of quiet, and reflection, which also offer a new perspective on this life. Once a blur, Joplin comes into focus during these private moments, and down to earth, too. Power locates something else in these letters. That (of course) would be the blues.

“Little Girl Blue” is weakest on Joplin’s musical apprenticeship, strongest on finding her humanity. (An abundance of concert clips nearly makes up for the former). But maybe the best bit of all: Dick Cavett reveals that he and Joplin had a long ago love affair. Imagine that.

BOTTOM LINE Fine, judicious, generous portrait of a lady who sang the blues.