local src=app.open(app.params.source)
local img=Image(src.cels[1].image)
local target_h=tonumber(app.params.height)
for pixel in img:pixels() do
  local c=pixel()
  if app.pixelColor.rgbaA(c)>=192 then
    pixel(app.pixelColor.rgba(app.pixelColor.rgbaR(c),app.pixelColor.rgbaG(c),app.pixelColor.rgbaB(c),255))
  else pixel(0) end
end
local cells=dofile(app.params.boxes)
local maxw,maxh=0,0
for _,box in ipairs(cells) do maxw,maxh=math.max(maxw,box.w),math.max(maxh,box.h) end
local factor=math.min(40/maxw,target_h/maxh)
local atlas=Image(144,64,ColorMode.RGB)
local frames={}
for index,box in ipairs(cells) do
  local crop=Image(box.w,box.h,ColorMode.RGB)
  crop:drawImage(img,Point(-box.x,-box.y))
  local tmp=Sprite(box.w,box.h,ColorMode.RGB)
  tmp.cels[1].image=crop
  local w,h=math.max(1,math.floor(box.w*factor+0.5)),math.max(1,math.floor(box.h*factor+0.5))
  app.command.SpriteSize{ui=false,width=w,height=h,method='nearest-neighbor'}
  local frame=Image(48,64,ColorMode.RGB)
  frame:drawImage(tmp.cels[1].image,Point(math.floor((48-w)/2),61-h))
  table.insert(frames,frame)
  local col,row=(index-1)%3,math.floor((index-1)/3)
  atlas:drawImage(frame,Point(col*48,row*64))
  tmp:close()
end
src:close()
local out=Sprite(144,64,ColorMode.RGB)
out.cels[1].image=atlas
out:saveAs(app.params.output)
out:close()
local gif=Sprite(48,64,ColorMode.RGB)
local seq={1,2,3,2}
for i,frame_index in ipairs(seq) do
  if i>1 then gif:newFrame() end
  gif.cels[i].image=Image(frames[frame_index])
  gif.frames[i].duration=0.16
end
app.command.SpriteSize{ui=false,width=144,height=192,method='nearest-neighbor'}
gif:saveAs(app.params.preview)
gif:close()
print('Exported '..#frames..' aligned pose frames; source max bounds '..maxw..'x'..maxh..'; uniform scale '..factor)