It's not "my own idea of what improvisation is". 2 quick questions (honest questions, not intended to insult you
):
-Have you ever actually heard Autumn Leaves?
-Did you actually watch the full performance?
I don't know how much you know about jazz, so I'm going to respond as though you know nothing (and hope that doesn't offend you if that's not the case!). When you learn a jazz tune from paper, all you're going to get 99% of the time is a lead sheat...i.e. just the melody and chord symbols. When you think about it, the chord symbols, while telling you the function of each chord and basic harmony, don't really give you all that much. Sometimes you'll get a specific inversion, but even that is wide open to interpretation of the player (and FWIW, I'm pretty sure Autumn leaves doesn't have inversions written in the real book). Autumn leaves has a 32 bar form...when you consider all the different ways to reinterpret each chord, the ways to voice lead from one to the next, consider possible substitutions and reharmonizations....there are well over thousands of different ways to play the chords to that song, all based pretty closely on the basic harmony laid out on the lead sheet. When you consider all the options available, and consider that these decisions are generally made on the spot (such as in the Ted Greene video in question), then I would say that it is absolutely a form of improvisation. Now, that's just for accompaniment. What ted is doing there is improvising an entire solo arrangement of the piece. During the head...he's playing the written melody, a bassline, and the chords (and again...he is going beyond simply reproducing a bare-bones rendition of what the written harmony is). After the head...he is improvising a melody, playing a bassline, and providing himself the chordal accompaniment. What I was getting at early with the "higher level of improv" comment was that he is improvising all those things at once. Furthermore, the way ted things about these things would make it a lot harder for most others to do. He doesn't think in terms of chords, he thinks in terms of individual voices. If he's going from one 4 note chord to another.....he's thinking of 4 individual melody lines rather than one chord movement. So in his head...he's improvising a melody, improvising a bassline, and improvising a few more individual voices to fill out the harmony...all at once based on simple chord symbols. In function, it's not that much of a leap....but to go from those chord symbols on a lead sheet to actually being able to do all that and to the level and extent that Ted does is simply mindblowing. Thus, my feelings that it takes a much higher level of understanding and ability to do what he was doing there than it does to improvise just a melody based off the same base material. There is a LOT more going on there than just decorating the melody.
I would agree that some things need to be judged from a practicallity standpoint as to whether or not they are improvisations according to the more commonly used definition....but to me, and everyone I've ever encountered in the genre or while playing/learning the stuff, what is going on in that video definitely fits the criteria for "improvisation".