diff --git a/pipi/filter/blur.c b/pipi/filter/blur.c
index 47af29a..8396341 100644
--- a/pipi/filter/blur.c
+++ b/pipi/filter/blur.c
@@ -45,7 +45,7 @@ pipi_image_t *pipi_gaussian_blur_ext(pipi_image_t *src, float rx, float ry,
     float *srcdata, *dstdata;
     double *kernel, *buffer;
     double K;
-    int x, y, i, w, h, kr, kw;
+    int x, y, i, w, h, kr, kw, gray;
 
     if(rx < BLUR_EPSILON) rx = BLUR_EPSILON;
     if(ry < BLUR_EPSILON) ry = BLUR_EPSILON;
@@ -53,14 +53,18 @@ pipi_image_t *pipi_gaussian_blur_ext(pipi_image_t *src, float rx, float ry,
     w = src->w;
     h = src->h;
 
-    srcp = pipi_getpixels(src, PIPI_PIXELS_RGBA_F);
+    gray = (src->last_modified == PIPI_PIXELS_Y_F);
+
+    srcp = gray ? pipi_getpixels(src, PIPI_PIXELS_Y_F)
+                : pipi_getpixels(src, PIPI_PIXELS_RGBA_F);
     srcdata = (float *)srcp->pixels;
 
     dst = pipi_new(w, h);
-    dstp = pipi_getpixels(dst, PIPI_PIXELS_RGBA_F);
+    dstp = gray ? pipi_getpixels(dst, PIPI_PIXELS_Y_F)
+                : pipi_getpixels(dst, PIPI_PIXELS_RGBA_F);
     dstdata = (float *)dstp->pixels;
 
-    buffer = malloc(w * h * 4 * sizeof(double));
+    buffer = malloc(w * h * (gray ? 1 : 4) * sizeof(double));
 
     kr = (int)(3. * rx + 1.99999);
     kw = 2 * kr + 1;
@@ -74,26 +78,48 @@ pipi_image_t *pipi_gaussian_blur_ext(pipi_image_t *src, float rx, float ry,
     {
         for(x = 0; x < w; x++)
         {
-            double R = 0., G = 0., B = 0., t = 0.;
-            int x2, off = 4 * (y * w + x);
-
-            for(i = -kr; i <= kr; i++)
+            if(gray)
             {
-                double f = kernel[i + kr];
+                double Y = 0., t = 0.;
+                int x2;
 
-                x2 = x + i;
-                if(x2 < 0) x2 = 0;
-                else if(x2 >= w) x2 = w - 1;
+                for(i = -kr; i <= kr; i++)
+                {
+                    double f = kernel[i + kr];
 
-                R += f * srcdata[(y * w + x2) * 4];
-                G += f * srcdata[(y * w + x2) * 4 + 1];
-                B += f * srcdata[(y * w + x2) * 4 + 2];
-                t += f;
-            }
+                    x2 = x + i;
+                    if(x2 < 0) x2 = 0;
+                    else if(x2 >= w) x2 = w - 1;
+
+                    Y += f * srcdata[y * w + x2];
+                    t += f;
+                }
 
-            buffer[off] = R / t;
-            buffer[off + 1] = G / t;
-            buffer[off + 2] = B / t;
+                buffer[y * w + x] = Y / t;
+            }
+            else
+            {
+                double R = 0., G = 0., B = 0., t = 0.;
+                int x2, off = 4 * (y * w + x);
+
+                for(i = -kr; i <= kr; i++)
+                {
+                    double f = kernel[i + kr];
+
+                    x2 = x + i;
+                    if(x2 < 0) x2 = 0;
+                    else if(x2 >= w) x2 = w - 1;
+
+                    R += f * srcdata[(y * w + x2) * 4];
+                    G += f * srcdata[(y * w + x2) * 4 + 1];
+                    B += f * srcdata[(y * w + x2) * 4 + 2];
+                    t += f;
+                }
+
+                buffer[off] = R / t;
+                buffer[off + 1] = G / t;
+                buffer[off + 2] = B / t;
+            }
         }
     }
 
@@ -111,26 +137,48 @@ pipi_image_t *pipi_gaussian_blur_ext(pipi_image_t *src, float rx, float ry,
     {
         for(x = 0; x < w; x++)
         {
-            double R = 0., G = 0., B = 0., t = 0.;
-            int y2, off = 4 * (y * w + x);
-
-            for(i = -kr; i <= kr; i++)
+            if(gray)
             {
-                double f = kernel[i + kr];
+                double Y = 0., t = 0.;
+                int y2;
 
-                y2 = y + i;
-                if(y2 < 0) y2 = 0;
-                else if(y2 >= h) y2 = h - 1;
+                for(i = -kr; i <= kr; i++)
+                {
+                    double f = kernel[i + kr];
 
-                R += f * buffer[(y2 * w + x) * 4];
-                G += f * buffer[(y2 * w + x) * 4 + 1];
-                B += f * buffer[(y2 * w + x) * 4 + 2];
-                t += f;
-            }
+                    y2 = y + i;
+                    if(y2 < 0) y2 = 0;
+                    else if(y2 >= h) y2 = h - 1;
+
+                    Y += f * buffer[y2 * w + x];
+                    t += f;
+                }
 
-            dstdata[off] = R / t;
-            dstdata[off + 1] = G / t;
-            dstdata[off + 2] = B / t;
+                dstdata[y * w + x] = Y / t;
+            }
+            else
+            {
+                double R = 0., G = 0., B = 0., t = 0.;
+                int y2, off = 4 * (y * w + x);
+
+                for(i = -kr; i <= kr; i++)
+                {
+                    double f = kernel[i + kr];
+
+                    y2 = y + i;
+                    if(y2 < 0) y2 = 0;
+                    else if(y2 >= h) y2 = h - 1;
+
+                    R += f * buffer[(y2 * w + x) * 4];
+                    G += f * buffer[(y2 * w + x) * 4 + 1];
+                    B += f * buffer[(y2 * w + x) * 4 + 2];
+                    t += f;
+                }
+
+                dstdata[off] = R / t;
+                dstdata[off + 1] = G / t;
+                dstdata[off + 2] = B / t;
+            }
         }
     }