diff --git a/pipi/filter/convolution.c b/pipi/filter/convolution.c
index 9657a70..b427e33 100644
--- a/pipi/filter/convolution.c
+++ b/pipi/filter/convolution.c
@@ -134,7 +134,7 @@ static pipi_image_t *T(conv)(pipi_image_t *src, int m, int n, double mat[])
     {
         for(x = 0; x < w; x++)
         {
-            double R = 0., G = 0., B = 0.;
+            double R = 0., G = 0., B = 0., A = 0.;
             double Y = 0.;
             int x2, y2, off = 4 * (y * w + x);
 
@@ -159,6 +159,7 @@ static pipi_image_t *T(conv)(pipi_image_t *src, int m, int n, double mat[])
                         R += f * srcdata[(y2 * w + x2) * 4];
                         G += f * srcdata[(y2 * w + x2) * 4 + 1];
                         B += f * srcdata[(y2 * w + x2) * 4 + 2];
+                        A += f * srcdata[(y2 * w + x2) * 4 + 3];
                     }
                 }
             }
@@ -170,6 +171,7 @@ static pipi_image_t *T(conv)(pipi_image_t *src, int m, int n, double mat[])
                 dstdata[off] = R < 0.0 ? 0.0 : R > 1.0 ? 1.0 : R;
                 dstdata[off + 1] = G < 0.0 ? 0.0 : G > 1.0 ? 1.0 : G;
                 dstdata[off + 2] = B < 0.0 ? 0.0 : B > 1.0 ? 1.0 : B;
+                dstdata[off + 3] = A < 0.0 ? 0.0 : A > 1.0 ? 1.0 : A;
             }
         }
     }
@@ -204,7 +206,7 @@ static pipi_image_t *T(sepconv)(pipi_image_t *src,
     {
         for(x = 0; x < w; x++)
         {
-            double R = 0., G = 0., B = 0.;
+            double R = 0., G = 0., B = 0., A = 0.;
             double Y = 0.;
             int x2, off = 4 * (y * w + x);
 
@@ -223,6 +225,7 @@ static pipi_image_t *T(sepconv)(pipi_image_t *src,
                     R += f * srcdata[(y * w + x2) * 4];
                     G += f * srcdata[(y * w + x2) * 4 + 1];
                     B += f * srcdata[(y * w + x2) * 4 + 2];
+                    A += f * srcdata[(y * w + x2) * 4 + 3];
                 }
             }
 
@@ -233,6 +236,7 @@ static pipi_image_t *T(sepconv)(pipi_image_t *src,
                 buffer[off] = R;
                 buffer[off + 1] = G;
                 buffer[off + 2] = B;
+                buffer[off + 3] = A;
             }
         }
     }
@@ -241,7 +245,7 @@ static pipi_image_t *T(sepconv)(pipi_image_t *src,
     {
         for(x = 0; x < w; x++)
         {
-            double R = 0., G = 0., B = 0.;
+            double R = 0., G = 0., B = 0., A = 0.;
             double Y = 0.;
             int y2, off = 4 * (y * w + x);
 
@@ -260,6 +264,7 @@ static pipi_image_t *T(sepconv)(pipi_image_t *src,
                     R += f * buffer[(y2 * w + x) * 4];
                     G += f * buffer[(y2 * w + x) * 4 + 1];
                     B += f * buffer[(y2 * w + x) * 4 + 2];
+                    A += f * buffer[(y2 * w + x) * 4 + 3];
                 }
             }
 
@@ -270,6 +275,7 @@ static pipi_image_t *T(sepconv)(pipi_image_t *src,
                 dstdata[off] = R < 0.0 ? 0.0 : R > 1.0 ? 1.0 : R;
                 dstdata[off + 1] = G < 0.0 ? 0.0 : G > 1.0 ? 1.0 : G;
                 dstdata[off + 2] = B < 0.0 ? 0.0 : B > 1.0 ? 1.0 : B;
+                dstdata[off + 3] = A < 0.0 ? 0.0 : A > 1.0 ? 1.0 : A;
             }
         }
     }