Almost there

demo.lua

@@ -1,3 +1,4 @@
+local cairo = require'cairo' --used to open the file
 local bitmap = require'bitmap' --used to read its content
 
 function int_hex(nb)
@@ -9,34 +10,38 @@ end
 io.write([[from draw import *
 ]])
 
-do --open image
-  local cairo = require'cairo' --used to open the file
-  local image = cairo.load_png(arg[1])
-  image_infos = {width = image:width(), height = image:height()}
-  image_bitmap = image:bitmap()
-end
-local getpixel, setpixel = bitmap.pixel_interface(image_bitmap)
-
-pallet = {} --will store colors
-pallet_last = 0
-
-io.write("width=", image_infos.width, "\n", [[data=b"]])
-
-for j = 1, image_infos.height, 1 do
-  for i = 1, image_infos.width, 1 do
-    r, g, b = getpixel(i, j)
-    if not pallet[r..","..g..","..b] then
-      pallet[r..","..g..","..b] = pallet_last
-      pallet_last = pallet_last + 1
-    end
-    io.write(int_hex(pallet[r..","..g..","..b]))
+for i = 1, 12, 1 do
+  do --open image
+    path = "spongebob/out-"
+    if i < 10 then path = path.."0" end
+    path = path..i.."0.png"
+    local image = cairo.load_png(path)
+    image_infos = {width = image:width(), height = image:height()}
+    image_bitmap = image:bitmap()
   end
-end
+  local getpixel, setpixel = bitmap.pixel_interface(image_bitmap)
 
---let's write the pallet
-io.write("\"\npallet={")
-for i, v in pairs(pallet) do
-  io.write(v, ":(", i, "),")
-end
+  pallet = {} --will store colors
+  pallet_last = 0
 
-io.write("}\ndraw(data,pallet,", image_infos.width, ")")
+  io.write("width=", image_infos.width, "\n", [[data=b"]])
+
+  for j = 1, image_infos.height, 1 do
+    for i = 1, image_infos.width, 1 do
+      r, g, b = getpixel(i, j)
+      if not pallet[r..","..g..","..b] then
+        pallet[r..","..g..","..b] = pallet_last
+        pallet_last = pallet_last + 1
+      end
+      io.write(int_hex(pallet[r..","..g..","..b]))
+    end
+  end
+
+  --let's write the pallet
+  io.write("\"\npallet={")
+  for i, v in pairs(pallet) do
+    io.write(v, ":(", i, "),")
+  end
+
+  io.write("}\ndraw(data,pallet,", image_infos.width, ")")
+end