16. A method of optimizing a program for creating of an image, the program being defined in a graphical programming language having a plurality of operators, said method being performed by a computer and comprising the steps of: (a) constructing at least one expression tree describing operations required to create the image; (b) transforming at least one portion of the expression tree in accordance with algebraic properties of the operators so as to reduce a corresponding execution time of a series of instructions derived from the expression tree without substantially altering an image created by the execution of the series of instructions; and (c) generating a corresponding series of instructions from the altered expression tree for creating the image; wherein said one portion is transformed in accordance with any one or more of the transformations selected from the group consisting of: (a over b) over c.fwdarw.a over (b over c), (a in b) in c.fwdarw.a in (b in c), (a plusC b) plusC c.fwdarw.a PlusC (b plusC c), (a plusW b) plusW c.fwdarw.a plusW (b plusW c), a xor b.fwdarw.xor a, a plusC b.fwdarw.plusC a, a plusW b.fwdarw.plusW a, a over b.fwdarw.b rover a, a rover b.fwdarw.over a, a in b.fwdarw.rin a, a rin b.fwdarw.b in a, a out b.fwdarw.b rout a, a rout b.fwdarw.b out a, a atop b.fwdarw.b ratop a, and a ratop b.fwdarw.b atop a.
16. A method of optimizing a program for creating of an image, the program being defined in a graphical programming language having a plurality of operators, said method being performed by a computer and comprising the steps of: (a) constructing at least one expression tree describing operations required to create the image; (b) transforming at least one portion of the expression tree in accordance with algebraic properties of the operators so as to reduce a corresponding execution time of a series of instructions derived from the expression tree without substantially altering an image created by the execution of the series of instructions; and (c) generating a corresponding series of instructions from the altered expression tree for creating the image; wherein said one portion is transformed in accordance with any one or more of the transformations selected from the group consisting of: (a over b) over c.fwdarw.a over (b over c), (a in b) in c.fwdarw.a in (b in c), (a plusC b) plusC c.fwdarw.a PlusC (b plusC c), (a plusW b) plusW c.fwdarw.a plusW (b plusW c), a xor b.fwdarw.xor a, a plusC b.fwdarw.plusC a, a plusW b.fwdarw.plusW a, a over b.fwdarw.b rover a, a rover b.fwdarw.over a, a in b.fwdarw.rin a, a rin b.fwdarw.b in a, a out b.fwdarw.b rout a, a rout b.fwdarw.b out a, a atop b.fwdarw.b ratop a, and a ratop b.fwdarw.b atop a. 17. A method according to claim 16, wherein said transformation step (b) further includes the steps of: determining an alternative form of expression of portions of said at least one expression tree; estimating a cost of execution of a corresponding series of instructions of said alternative form of expression, and altering the portion to said alternative form of expression when the cost of execution of said alternative form of the portion is lower than the cost of execution of a present form of the portion.