AT the Sundance Film Festival earlier this year, I wheedled a ticket to “Becoming Chaz,” a documentary about the sex change of Chastity Bono. Having long admired the Fenton Bailey and Randy Barbato World of Wonder productions — slyly edu-taining films like “The Eyes of Tammy Faye” and oodles of just-louche-enough-for-reality-TV shows like “RuPaul’s Drag Race” — I anticipated their usual mix of human interest, alternative lifestyle and salacious tabloid.

This unflinchingly personal film, which will have its premiere on Oprah Winfrey’s network on Tuesday, details Chastity Bono’s journey from her spangled childhood in rhinestone pantsuits on “The Sonny and Cher Comedy Hour” to a more recent two years in her televised life: Chastity, now Chaz, invited cameras to witness the searingly intimate experience of his gender transition.

Chaz, 42, and Jennifer Elia, his longtime girlfriend, must navigate his hormone injections, mood swings and personality changes, and live through a medical procedure that is part of the process of making Chaz a legal male in the State of California: he undergoes “top surgery” and has his breasts removed.

The operation is so graphic, and such a commitment — physically, emotionally and financially — that as a wincing viewer you come away with a palpable understanding of how unendurably he must be suffering in his body to want to have his own sex characteristics amputated.