BL [n1],n2 n1: Image plane of bitplane <last image plane> n2: Logical expression of bitplanes <>n1 is the image plane onto which an O-map (created with BBT) has been loaded. The data in this image plane are organized in bitplanes.
n2 is a logical expression consisting of any syntactically correct combination of logical operators, bitplane numbers, and parentheses. The simple logical operators are as follows:
Operator Type Example +-------------------------+ AND binary 1 AND 2 OR binary 3 OR 4 XOR binary 1 XOR 4 SUB binary 5 SUB 3 NOT unary NOT (6)These simple operators can be combined into more complex forms such as:
DCP>BL1, (1 AND 2) XOR (3 OR 4) XOR NOT (6)The simple logical operators have the following truth tables:
i | j | i AND j i | j | i OR j i | j | i XOR j +--+---+-------- ---+---+------- ---+---+-------- 0 | 0 | 0 0 | 0 | 0 0 | 0 | 0 0 | 1 | 0 0 | 1 | 1 0 | 1 | 1 1 | 0 | 0 1 | 0 | 1 1 | 0 | 1 1 | 1 | 1 1 | 1 | 1 1 | 1 | 0 i | j | i SUB j = i AND NOT j i | NOT i +--+---+-------- ---+------ 0 | 0 | 0 0 | 1 0 | 1 | 0 1 | 0 1 | 0 | 1 1 | 1 | 0The logical operation is a non-destructive operation (does not change the data), that is performed using the display pseudocolour table. Each logical expression causes the colour table to be manipulated such that only the results of the logical expression are visible. The colour in which the results are shown can be modified with the BR (Bitplane Result) command.
See the task OLO (Overlay Logical Operation) for database logical operations using a pseudocolour table saved from the display.