diff --git a/src/app/util/layer_boundaries.cpp b/src/app/util/layer_boundaries.cpp
index 4eb1c548d..5c94a907d 100644
--- a/src/app/util/layer_boundaries.cpp
+++ b/src/app/util/layer_boundaries.cpp
@@ -37,63 +37,7 @@ void select_layer_boundaries(Layer* layer,
   const Cel* cel = layer->cel(frame);
   if (cel) {
     const Image* image = cel->image();
-    if (image) {
-      newMask.replace(cel->bounds());
-      newMask.freeze();
-      {
-        LockImageBits<BitmapTraits> maskBits(newMask.bitmap());
-        auto maskIt = maskBits.begin();
-        auto maskEnd = maskBits.end();
-
-        switch (image->pixelFormat()) {
-
-          case IMAGE_RGB: {
-            LockImageBits<RgbTraits> rgbBits(image);
-            auto rgbIt = rgbBits.begin();
-#if _DEBUG
-            auto rgbEnd = rgbBits.end();
-#endif
-            for (; maskIt != maskEnd; ++maskIt, ++rgbIt) {
-              ASSERT(rgbIt != rgbEnd);
-              color_t c = *rgbIt;
-              *maskIt = (rgba_geta(c) >= 128); // TODO configurable threshold
-            }
-            break;
-          }
-
-          case IMAGE_GRAYSCALE: {
-            LockImageBits<GrayscaleTraits> grayBits(image);
-            auto grayIt = grayBits.begin();
-#if _DEBUG
-            auto grayEnd = grayBits.end();
-#endif
-            for (; maskIt != maskEnd; ++maskIt, ++grayIt) {
-              ASSERT(grayIt != grayEnd);
-              color_t c = *grayIt;
-              *maskIt = (graya_geta(c) >= 128); // TODO configurable threshold
-            }
-            break;
-          }
-
-          case IMAGE_INDEXED: {
-            const doc::color_t maskColor = image->maskColor();
-            LockImageBits<IndexedTraits> idxBits(image);
-            auto idxIt = idxBits.begin();
-#if _DEBUG
-            auto idxEnd = idxBits.end();
-#endif
-            for (; maskIt != maskEnd; ++maskIt, ++idxIt) {
-              ASSERT(idxIt != idxEnd);
-              color_t c = *idxIt;
-              *maskIt = (c != maskColor);
-            }
-            break;
-          }
-
-        }
-      }
-      newMask.unfreeze();
-    }
+    newMask.fromImage(image, cel->bounds().origin());
   }
 
   try {
diff --git a/src/doc/mask.cpp b/src/doc/mask.cpp
index baadd491a..140257fa0 100644
--- a/src/doc/mask.cpp
+++ b/src/doc/mask.cpp
@@ -10,9 +10,8 @@
 #endif
 
 #include "doc/mask.h"
-
-#include "base/memory.h"
 #include "doc/image_impl.h"
+#include "gfx/point.h"
 
 #include <cstdlib>
 #include <cstring>
@@ -129,6 +128,67 @@ void Mask::copyFrom(const Mask* sourceMask)
   }
 }
 
+void Mask::fromImage(const Image* image, const gfx::Point& maskOrigin)
+{
+  if (image) {
+    replace(image->bounds().setOrigin(maskOrigin));
+    freeze();
+    {
+      LockImageBits<BitmapTraits> maskBits(bitmap());
+      auto maskIt = maskBits.begin();
+      auto maskEnd = maskBits.end();
+
+      switch (image->pixelFormat()) {
+
+        case IMAGE_RGB: {
+          LockImageBits<RgbTraits> rgbBits(image);
+          auto rgbIt = rgbBits.begin();
+#if _DEBUG
+          auto rgbEnd = rgbBits.end();
+#endif
+          for (; maskIt != maskEnd; ++maskIt, ++rgbIt) {
+            ASSERT(rgbIt != rgbEnd);
+            color_t c = *rgbIt;
+            *maskIt = (rgba_geta(c) >= 128); // TODO configurable threshold
+          }
+          break;
+        }
+
+        case IMAGE_GRAYSCALE: {
+          LockImageBits<GrayscaleTraits> grayBits(image);
+          auto grayIt = grayBits.begin();
+#if _DEBUG
+          auto grayEnd = grayBits.end();
+#endif
+          for (; maskIt != maskEnd; ++maskIt, ++grayIt) {
+            ASSERT(grayIt != grayEnd);
+            color_t c = *grayIt;
+            *maskIt = (graya_geta(c) >= 128); // TODO configurable threshold
+          }
+          break;
+        }
+
+        case IMAGE_INDEXED: {
+          const doc::color_t maskColor = image->maskColor();
+          LockImageBits<IndexedTraits> idxBits(image);
+          auto idxIt = idxBits.begin();
+#if _DEBUG
+          auto idxEnd = idxBits.end();
+#endif
+          for (; maskIt != maskEnd; ++maskIt, ++idxIt) {
+            ASSERT(idxIt != idxEnd);
+            color_t c = *idxIt;
+            *maskIt = (c != maskColor);
+          }
+          break;
+        }
+
+      }
+    }
+    unfreeze();
+  }
+}
+
 void Mask::offsetOrigin(int dx, int dy)
 {
   m_bounds.offset(dx, dy);
diff --git a/src/doc/mask.h b/src/doc/mask.h
index be6f0b8ee..e02465904 100644
--- a/src/doc/mask.h
+++ b/src/doc/mask.h
@@ -76,6 +76,7 @@ namespace doc {
 
     // Copies the data from the given mask.
     void copyFrom(const Mask* sourceMask);
+    void fromImage(const Image* image, const gfx::Point& maskOrigin);
 
     // Replace the whole mask with the given region.
     void replace(const gfx::Rect& bounds);