function math.round(x) return math.floor(x+0.5) end

newwidth=math.round(width*zoom)
newheight=math.round(height*zoom)
newpixels = {}

for y=0,newheight-1 do
  for x=0,newwidth-1 do
    newpixels[y*newwidth+x+1] = pixels[math.floor(x/zoom)+math.floor(y/zoom)*width+1]
  end
end

width=newwidth
height=newheight
pixels=newpixels
newpixels=nil