diff --git a/src/interface/desktop/WidgetPreviewCanvas.cpp b/src/interface/desktop/WidgetPreviewCanvas.cpp
index e1463f9..36ade57 100644
--- a/src/interface/desktop/WidgetPreviewCanvas.cpp
+++ b/src/interface/desktop/WidgetPreviewCanvas.cpp
@@ -25,7 +25,7 @@ void WidgetPreviewCanvas::setCanvas(const Canvas *canvas)
     this->canvas = canvas;
 }
 
-void WidgetPreviewCanvas::paintEvent(QPaintEvent *event)
+void WidgetPreviewCanvas::paintEvent(QPaintEvent *)
 {
     QPainter painter(this);
     painter.drawImage(0, 0, *pixbuf);
diff --git a/src/render/software/Canvas.cpp b/src/render/software/Canvas.cpp
index 4e4e746..7cf1439 100644
--- a/src/render/software/Canvas.cpp
+++ b/src/render/software/Canvas.cpp
@@ -70,7 +70,7 @@ void Canvas::setSize(int width, int height)
     this->height = height;
 
     // Smaller preview
-    while (width > 800 and height > 800)
+    while (width > 1000 or height > 700)
     {
         width = width / 2;
         height = height / 2;
diff --git a/src/render/software/CanvasPreview.cpp b/src/render/software/CanvasPreview.cpp
index f7cf1fc..5012911 100644
--- a/src/render/software/CanvasPreview.cpp
+++ b/src/render/software/CanvasPreview.cpp
@@ -7,6 +7,12 @@
 
 #include <cassert>
 
+#define CHECK_COORDINATES(_x_, _y_) \
+    assert(_x_ >= 0); \
+    assert(_y_ >= 0); \
+    assert(_x_ < this->width); \
+    assert(_y_ < this->height) \
+
 CanvasPreview::CanvasPreview()
 {
     width = 1;
@@ -34,6 +40,13 @@ CanvasPreview::~CanvasPreview()
     delete profile;
 }
 
+const Color &CanvasPreview::getFinalPixel(int x, int y) const
+{
+    CHECK_COORDINATES(x, y);
+
+    return pixels[y * width + x];
+}
+
 void CanvasPreview::setSize(int real_width, int real_height, int preview_width, int preview_height)
 {
     lock->acquire();
@@ -110,8 +123,11 @@ void CanvasPreview::pushPixel(int real_x, int real_y, const Color &old_color, co
 
     if (scaled)
     {
-        x = round(real_x / factor_x);
-        y = round(real_y / factor_y);
+        x = int(real_x / factor_x);
+        y = int(real_y / factor_y);
+
+        x = (x >= width) ? width - 1 : x;
+        y = (y >= height) ? height - 1 : y;
     }
     else
     {
@@ -119,7 +135,7 @@ void CanvasPreview::pushPixel(int real_x, int real_y, const Color &old_color, co
         y = real_y;
     }
 
-    // TODO Assert-check on x and y
+    CHECK_COORDINATES(x, y);
 
     Color* pixel = pixels + (y * width + x);
     pixel->r = pixel->r - old_color.r / factor + new_color.r / factor;
diff --git a/src/render/software/CanvasPreview.h b/src/render/software/CanvasPreview.h
index f67cc39..dbcc0e4 100644
--- a/src/render/software/CanvasPreview.h
+++ b/src/render/software/CanvasPreview.h
@@ -18,6 +18,8 @@ public:
     inline int getWidth() const {return width;}
     inline int getHeight() const {return height;}
 
+    const Color &getFinalPixel(int x, int y) const;
+
     void setSize(int real_width, int real_height, int preview_width, int preview_height);
     void reset();
 
diff --git a/src/tests/CanvasPortion_Test.cpp b/src/tests/CanvasPortion_Test.cpp
index b88137c..c3e8cd2 100644
--- a/src/tests/CanvasPortion_Test.cpp
+++ b/src/tests/CanvasPortion_Test.cpp
@@ -21,6 +21,8 @@ TEST(CanvasPortion, pushFragment)
     int count;
 
     portion.setSize(50, 50);
+    portion.preparePixels();
+
     portion.pushFragment(10, 15, pushed);
 
     count = portion.getFragmentCount(10, 14);
@@ -40,6 +42,7 @@ TEST(CanvasPortion, pushFragment_opaque)
     CanvasFragment pushed;
 
     portion.setSize(10, 10);
+    portion.preparePixels();
 
     pushed = CanvasFragment(2.0, VECTOR_ZERO, 0);
     portion.pushFragment(2, 2, pushed);
@@ -66,6 +69,7 @@ TEST(CanvasPortion, pushFragment_transparent)
     CanvasFragment pushed;
 
     portion.setSize(10, 10);
+    portion.preparePixels();
 
     pushed = CanvasFragment(2.0, VECTOR_ZERO, 0, false);
     portion.pushFragment(2, 2, pushed);
@@ -92,6 +96,8 @@ TEST(CanvasPortion, clear)
     CanvasFragment fragment;
 
     portion.setSize(10, 10);
+    portion.preparePixels();
+
     portion.pushFragment(5, 5, fragment);
 
     EXPECT_EQ(0, portion.getFragmentCount(4, 5));
diff --git a/src/tests/CanvasPreview_Test.cpp b/src/tests/CanvasPreview_Test.cpp
new file mode 100644
index 0000000..e754267
--- /dev/null
+++ b/src/tests/CanvasPreview_Test.cpp
@@ -0,0 +1,50 @@
+#include "BaseTestCase.h"
+
+#include "CanvasPreview.h"
+#include "Color.h"
+
+TEST(CanvasPreview, setSize)
+{
+    CanvasPreview preview;
+
+    preview.setSize(800, 600, 400, 300);
+
+    EXPECT_EQ(400, preview.getWidth());
+    EXPECT_EQ(300, preview.getHeight());
+}
+
+TEST(CanvasPreview, pushPixel_accumulate)
+{
+    CanvasPreview preview;
+    Color col;
+    preview.setSize(800, 600, 400, 300);
+
+    col = preview.getFinalPixel(0, 0);
+    EXPECT_COLOR_RGBA(col, 0.0, 0.0, 0.0, 1.0);
+
+    preview.pushPixel(0, 0, COLOR_BLACK, COLOR_RED);
+    col = preview.getFinalPixel(0, 0);
+    EXPECT_COLOR_RGBA(col, 0.25, 0.0, 0.0, 1.0);
+
+    preview.pushPixel(0, 1, COLOR_BLACK, COLOR_BLUE);
+    col = preview.getFinalPixel(0, 0);
+    EXPECT_COLOR_RGBA(col, 0.25, 0.0, 0.25, 1.0);
+
+    preview.pushPixel(0, 2, COLOR_BLACK, COLOR_BLUE);
+    col = preview.getFinalPixel(0, 0);
+    EXPECT_COLOR_RGBA(col, 0.25, 0.0, 0.25, 1.0);
+    col = preview.getFinalPixel(0, 1);
+    EXPECT_COLOR_RGBA(col, 0.0, 0.0, 0.25, 1.0);
+
+    preview.pushPixel(0, 1, COLOR_BLUE, COLOR_GREEN);
+    col = preview.getFinalPixel(0, 0);
+    EXPECT_COLOR_RGBA(col, 0.25, 0.25, 0.0, 1.0);
+}
+
+TEST(CanvasPreview, pushPixel_border)
+{
+    CanvasPreview preview;
+    preview.setSize(759, 237, 9, 14);
+
+    preview.pushPixel(759, 237, COLOR_BLACK, COLOR_RED);
+}
diff --git a/src/tests/tests.pro b/src/tests/tests.pro
index 2efe000..481b17a 100644
--- a/src/tests/tests.pro
+++ b/src/tests/tests.pro
@@ -21,7 +21,8 @@ SOURCES += main.cpp \
     VertexArray_Test.cpp \
     FractalNoise_Test.cpp \
     Canvas_Test.cpp \
-    CanvasPortion_Test.cpp
+    CanvasPortion_Test.cpp \
+    CanvasPreview_Test.cpp
 
 HEADERS += \
     BaseTestCase.h