Antialiasing in QB64

I made an antialiasing program - it scans the screen for pixels which need to be antialiased(edge pixels) and then blurs them accordingly. The problem is, it doesn't do anything. This is my source code :

SUB antialias (screenx, screeny)
FOR dx = 1 TO screenx - 1
FOR dy = 1 TO screeny - 1
op = POINT(dx, dy)
ra = 0
ba = 0
ga = 0
FOR cx = -1 TO 1
FOR cy = -1 TO 1
cp = POINT(dx + cx, dy + cy)
comparison = ABS(_RED32(op) - _RED32(cp)) + ABS(_BLUE32(op) - _BLUE32(cp)) + ABS(_GREEN32(cp) - _GREEN32(op))
IF comparison > 100 THEN
difpix = difpix + 1
END IF
ra = ra + (_RED32(cp) / 9)
ba = ba + (_BLUE32(cp) / 9)
ga = ga + (_GREEN32(cp) / 9)
NEXT cy
NEXT cx
IF difpix >= 1 AND difpix <= 4 THEN
difpix = 0
PSET (dx, dy), _RGB(ra, ga, ba)
END IF
NEXT dy
NEXT dx
END SUB