qb q's:

how big an aray  to  hold a screen of graphics (screen 12, i.e.  640 * 480)
?
how to declare it
?

is the following code optimum ?
does it squander ram ?

                ------------
DECLARE SUB GTPT ()
DECLARE SUB ini ()
'---- test graphics get put  bsave dsave
DEFINT A-Z
X = 2: Y = 32000: DIM SHARED ARAY(X, Y)
'X = 1: Y = 32000: DIM SHARED ARAY(X, -Y TO Y)
ini
GTPT

SUB GTPT
GET (0, 0)-(639, 479), ARAY
LOCATE 4, 44: INPUT "pRESS A KEY"; A$
'PRINT ARAY(0, 0); ARAY(1, 0)
'       ARAY(0, 0) * ARAY(1, 0)
BSAVE "VGA.IMG", 0 + VARPTR(ARAY(0, 0)), 64000
LOCATE 5, 44: INPUT "pRESS A KEY"; A$
CLS
LOCATE 6, 44: INPUT "pRESS A KEY"; A$
BLOAD "VGA.IMG", 0
END SUB

SUB ini
CLS : SCREEN 12
DEF SEG = &HA000
LINE (0, 0)-(639, 479), , B
CIRCLE STEP(0, 0), 33
END SUB
                ------------

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Screen 12 requires more than 64k so you'll have to take it in 2 files.
BSAVE/BLOAD only accepts (AFAIK) 64k.

The formula for computing array size is something like...

Cols%         = ((X2%-X1%) + 6 ) \ 8
Rows%         = (Y2%-Y1%)+1
Pixels%       = ( Cols% * Rows% )
BitsPerPlane% = 4  ' screen 12
Bytes%        = ( ( Pixels% * BitsPerPlane% ) \ 8 ) + 4
Elements%     = ( Bytes% \ 2 ) - 1

DIM Array%(Elements%)