diff --git a/convert_data.lua b/convert_data.lua
index 4cebfbd..181b292 100644
--- a/convert_data.lua
+++ b/convert_data.lua
@@ -1,12 +1,13 @@
+require 'pl'
 local __FILE__ = (function() return string.gsub(debug.getinfo(2, 'S').source, "^@", "") end)()
 package.path = path.join(path.dirname(__FILE__), "lib", "?.lua;") .. package.path
 
-require 'pl'
 require 'image'
 local compression = require 'compression'
 local settings = require 'settings'
 local image_loader = require 'image_loader'
 local iproc = require 'iproc'
+local alpha_util = require 'alpha_util'
 
 local function crop_if_large(src, max_size)
    local tries = 4
@@ -35,25 +36,24 @@ local function load_images(list)
       local line = lines[i]
       local im, meta = image_loader.load_byte(line)
       if meta and meta.alpha then
-	 io.stderr:write(string.format("\n%s: skip: image has alpha channel.\n", line))
-      else
-	 if settings.max_training_image_size > 0 then
-	    im = crop_if_large(im, settings.max_training_image_size)
-	 end
-	 im = iproc.crop_mod4(im)
-	 local scale = 1.0
-	 if settings.random_half_rate > 0.0 then
-	    scale = 2.0
-	 end
-	 if im then
-	    if im:size(2) > (settings.crop_size * scale + MARGIN) and im:size(3) > (settings.crop_size * scale + MARGIN) then
-	       table.insert(x, compression.compress(im))
-	    else
-	       io.stderr:write(string.format("\n%s: skip: image is too small (%d > size).\n", line, settings.crop_size * scale + MARGIN))
-	    end
+	 im = alpha_util.fill(im, meta.alpha, torch.random(0, 1))
+      end
+      if settings.max_training_image_size > 0 then
+	 im = crop_if_large(im, settings.max_training_image_size)
+      end
+      im = iproc.crop_mod4(im)
+      local scale = 1.0
+      if settings.random_half_rate > 0.0 then
+	 scale = 2.0
+      end
+      if im then
+	 if im:size(2) > (settings.crop_size * scale + MARGIN) and im:size(3) > (settings.crop_size * scale + MARGIN) then
+	    table.insert(x, compression.compress(im))
 	 else
-	    io.stderr:write(string.format("\n%s: skip: load error.\n", line))
+	    io.stderr:write(string.format("\n%s: skip: image is too small (%d > size).\n", line, settings.crop_size * scale + MARGIN))
 	 end
+      else
+	 io.stderr:write(string.format("\n%s: skip: load error.\n", line))
       end
       xlua.progress(i, #lines)
       if i % 10 == 0 then
diff --git a/lib/alpha_util.lua b/lib/alpha_util.lua
index 82305eb..ad8266f 100644
--- a/lib/alpha_util.lua
+++ b/lib/alpha_util.lua
@@ -63,6 +63,26 @@ function alpha_util.composite(rgb, alpha, model2x)
    out[4]:copy(alpha)
    return out
 end
+function alpha_util.fill(fg, alpha, val)
+   assert(fg:size(2) == alpha:size(2) and fg:size(3) == alpha:size(3))
+   local conversion = false
+   fg, conversion = iproc.byte2float(fg)
+   val = val or 0
+   fg = fg:clone()
+   bg = fg:clone():fill(val)
+   bg[1]:cmul(1-alpha)
+   bg[2]:cmul(1-alpha)
+   bg[3]:cmul(1-alpha)
+   fg[1]:cmul(alpha)
+   fg[2]:cmul(alpha)
+   fg[3]:cmul(alpha)
+
+   local ret = bg:add(fg)
+   if conversion then
+      ret = iproc.float2byte(ret)
+   end
+   return ret
+end
 
 local function test()
    require 'sys'