diff --git a/src/core/transformations/convolution.cpp b/src/core/transformations/convolution.cpp
index 0e3f293..30f6683 100644
--- a/src/core/transformations/convolution.cpp
+++ b/src/core/transformations/convolution.cpp
@@ -25,7 +25,7 @@ math::matrix<float> Convolution::getMask(int size, Mode mode = Normalize)
     for (int i=0; i<size; ++i) {
         for (int j=0; j<size; ++j) {
 
-            if (i / 2 == size / 2)
+            if (i / 2 == size / 2 && j / 2 == size / 2)
                 mask[i][j] = 1;
             else
                 mask[i][j] = 0;
diff --git a/src/core/transformations/edge_zero.cpp b/src/core/transformations/edge_zero.cpp
index a22e767..ff20e2d 100644
--- a/src/core/transformations/edge_zero.cpp
+++ b/src/core/transformations/edge_zero.cpp
@@ -21,23 +21,25 @@ PNM* EdgeZeroCrossing::transform()
     double sigma = getParameter("sigma").toDouble();
     int    t     = getParameter("threshold").toInt();
 
-    PNM* newImage = new PNM(width, height, QImage::Format_Grayscale8);
+    PNM* newImage = new PNM(width, height, image->format());
     EdgeLaplaceOfGauss log(newImage);
+    log.setParameter("size", getParameter("size"));
+    log.setParameter("sigma", getParameter("sigma"));
+
+    Transformation laplasjan(log.transform());
 
     int v0 = 128;
+    int half = size/2;
 
     for (int x=0;x<width;++x) {
         for (int y=0;y<height;++y) {
-            float lapsjan = EdgeLaplaceOfGauss::getLoG(x,y, sigma) * v0;
-            math::matrix<float> mask = log.getMask(size, sigma, RepeatEdge);
+            math::matrix<float> mask = laplasjan.getWindow(x, y, size, LChannel, RepeatEdge);
 
             float max = mask.max();
             float min = mask.min();
+            int gray = (min < (v0 - t) && max > (v0 + t)) ? mask(half, half) : 0;
 
-            if (min < v0 - t && max > v0 + t)
-                newImage->setPixel(x,y, QColor(255, 255, 255).rgb());
-            else
-                newImage->setPixel(x,y, QColor(0, 0, 0).rgb());
+            newImage->setPixel(x,y, QColor(gray, gray, gray).rgb());
         }
     }