functions in graph.i - b

    bytscl(z)  
 or bytscl(z, top=max_byte, cmin=lower_cutoff, cmax=upper_cutoff)  


returns a char array of the same shape as Z, with values linearly  
scaled to the range 0 to one less than the current palette size.  
If MAX_BYTE is specified, the scaled values will run from 0 to  
MAX_BYTE instead.  
If LOWER_CUTOFF and/or UPPER_CUTOFF are specified, Z values outside  
this range are mapped to the cutoff value; otherwise the linear  
scaling maps the extreme values of Z to 0 and MAX_BYTE.  
Builtin function, documented at i0/graph.i   line 1339