local source=app.open(app.params.source)
local src=Image(source.cels[1].image)
local count=tonumber(app.params.grid or '4')
local atlas=Image(count*32,count*32,ColorMode.RGB)
for row=0,count-1 do
  for col=0,count-1 do
    local x0,y0=math.floor(col*src.width/count)+4,math.floor(row*src.height/count)+4
    local side=math.min(math.floor((col+1)*src.width/count)-x0-4,math.floor((row+1)*src.height/count)-y0-4)
    local image=Image(side,side,ColorMode.RGB)
    image:drawImage(src,Point(-x0,-y0))
    local tmp=Sprite(side,side,ColorMode.RGB)
    tmp.cels[1].image=image
    app.command.SpriteSize{ui=false,width=32,height=32,method='nearest-neighbor'}
    atlas:drawImage(tmp.cels[1].image,Point(col*32,row*32))
    tmp:close()
  end
end
source:close()
local out=Sprite(count*32,count*32,ColorMode.RGB)
out.cels[1].image=atlas
out:saveAs(app.params.output)
out:close()