Diana Krall: Live at the Montreal Jazz Festival is a portrait of an already-accomplished musician in the process of evolving into a great artist. Always a fine jazz pianist, an expressive singer, and a capable interpreter (mostly of the Great American Songbook), Krall spent little time developing an original voice prior to her marriage to Elvis Costello and her CDThe Girl in the Other Room, which features multiple songwriting collaborations with Costello as well as more adventurous choices in cover material (Joni Mitchell's "Black Crow," Tom Waits's "Temptation"). That 2004 recording is the centerpiece of this concert; fully nine of the 13 selections here, including the Waits and Mitchell songs as well as five Costello-Krall compositions, were drawn from it. Purists may lament the lessening of the straight-ahead jazz element in Krall's music (indeed, with its simple major chords and countryish lilt, the original "Narrow Daylight" will inevitably invite comparisons to Norah Jones). But Krall and her excellent band still swing mightily (cf. an extended version of the standard "All or Nothing at All") and improvise like the seasoned jazz pros they are. It's a heady combination: Krall is at least as good an instrumentalist as her contemporaries; add to that her singing and now an interest in songwriting that reflects the influence of pop music as well as jazz, and you have a genuinely unique talent.