Fantasia Barrino doesn't do anything half-ass, evident in the fact that she was singing her heart out during a table read for her new film ... just imagine how the real thing sounds.

The "American Idol" alum is part of the star-studded cast for "The Color Purple" -- which just got released into theaters today ... and which is stirring up a lot of Oscar buzz, not to mention a ton of praise for the musical performances -- including one from Fantasia.

She handles one big number in there, in particular, called "I'm Here" ... and on Sunday, her costar Colman Domingo posted a video from their final table read as a cast last year.

Check it out ... it's pretty incredible to see. Fantasia is fully in character as Celie, and she's belting out this song with everything she's got -- which makes for an awesome showcasing of her talent. You can tell the other actors were impressed, encouraging her along the way.

Fantasia has sung this song before ... as she played this exact role for the Broadway version of 'TCP' -- and now, she'll be doing it for the big screen -- which is pretty exciting to see.

The reviews for this film are pretty stellar, and it should make a splash at the box office.

Mind you, this version of "The Color Purple" is a full-blown musical ... so we're sure to see/hear a lot more performances like this one -- and the early word is, 'TCP' is a frontrunner for Best Picture at next year's Oscars ceremony since it's so freaking good.