diff --git a/init.lua b/init.lua
index 89abffe..86db4c9 100644
--- a/init.lua
+++ b/init.lua
@@ -13,7 +13,7 @@ local function get_palette_of_image_data (data)
     --
     for x = 0, data:getWidth() - 1 do
         for y = 0, data:getHeight() - 1 do
-            local r, g, b  =  data:getPixel(x, y)
+            local r, g, b, a  =  data:getPixel(x, y)
             if not has_seen[r]       then  has_seen[r]    = {}  end
             if not has_seen[r][g]    then  has_seen[r][g] = {}  end
             if not has_seen[r][g][b] then
@@ -52,7 +52,7 @@ local function apply_change_palette (data, change_palette)
     assert(change_palette)
     --
     local change_tree  =  change_palette_to_dim_tree(change_palette)
-    local function map (x, y, r, g, b, a)
+    local function map (_x, _y, r, g, b, a)
         local c  =  change_tree[r][g][b]
         return c[1], c[2], c[3], a
     end