diff --git a/lib/alpha_util.lua b/lib/alpha_util.lua
index 9105f06..6a0228b 100644
--- a/lib/alpha_util.lua
+++ b/lib/alpha_util.lua
@@ -5,15 +5,15 @@ local iproc = require 'iproc'
 local gm = require 'graphicsmagick'
 
 alpha_util = {}
-alpha_util.sum2d = nn.SpatialConvolutionMM(1, 1, 3, 3, 1, 1, 1, 1):cuda()
-alpha_util.sum2d.weight:fill(1)
-alpha_util.sum2d.bias:zero()
 
 function alpha_util.make_border(rgb, alpha, offset)
    if not alpha then
       return rgb
    end
-   
+   local sum2d = nn.SpatialConvolutionMM(1, 1, 3, 3, 1, 1, 1, 1):cuda()
+   sum2d.weight:fill(1)
+   sum2d.bias:zero()
+
    local mask = alpha:clone()
    mask[torch.gt(mask, 0.0)] = 1
    mask[torch.eq(mask, 0.0)] = 0
@@ -26,10 +26,10 @@ function alpha_util.make_border(rgb, alpha, offset)
    rgb[3][mask_nega] = 0
 
    for i = 1, offset do
-      local mask_weight = alpha_util.sum2d:forward(mask:cuda()):float()
+      local mask_weight = sum2d:forward(mask:cuda()):float()
       local border = rgb:clone()
       for j = 1, 3 do
-	 border[j]:copy(alpha_util.sum2d:forward(rgb[j]:reshape(1, rgb:size(2), rgb:size(3)):cuda()))
+	 border[j]:copy(sum2d:forward(rgb[j]:reshape(1, rgb:size(2), rgb:size(3)):cuda()))
 	 border[j]:cdiv((mask_weight + eps))
 	 rgb[j][mask_nega] = border[j][mask_nega]
       end