diff --git a/scenePyramid.py b/scenePyramid.py
index e21f9adbdd21badfa1441e41ec7cdfa66739810a..3828c118848a78348dac9ea22fece7761487a69f 100644
--- a/scenePyramid.py
+++ b/scenePyramid.py
@@ -155,17 +155,18 @@ class ScenePyramid:
         if slice_changed:
             self.resetScene()
 
-        # map viewport to scene
-        view_origin = self.view.mapToScene(0, 0)
-        view_max_x_y = self.view.mapToScene(self.view.width(), self.view.height())
-
         # get scene origin (given in microscope coords) in pixel coords
         scene_origin_x, scene_origin_y = (0, 0)  # self.dataset.mapToPixel(p, self.microscopeMode, force=True)
 
+        # map viewport to scene
+        view_origin = self.view.mapToScene(scene_origin_x, scene_origin_y)
+        view_max_x_y = self.view.mapToScene(self.view.width(), self.view.height())
+
         # default width, height of view tiles
         view_tile_height, view_tile_width = self.tileDim
 
         inv_scaling = (1 / self.scalingFactor) ** self.currentSlice
+        assert inv_scaling >= 1
 
         if self.currentSlice in self.tileWorkingSets:
             for i in self.tileWorkingSets[self.currentSlice]:
@@ -178,9 +179,15 @@ class ScenePyramid:
                         tile_origin_x = max(0, i * view_tile_width) + scene_origin_x
                         tile_origin_y = max(0, j * view_tile_height) + scene_origin_y
 
-                        # view tile is of constant size, but will be scaled according to slice number (scaling)
-                        # so its appearent size in the scene will be bigger
-                        # and it will appear at a different position
+                        '''
+                        on higher slice numbers we use fewer lower res tiles to save memory
+                        as all tiles on all slices are equal of size, for keeping the same apparent size of the scene,
+                        we need to scale up the used tiles and shift there origin/position
+                        view tiles are of constant size, but with higher scale (showing lower resolution) they will need
+                        to be scaled up according to slice number
+                        tiles will be rendered scale times bigger so its (apparent) size in the scene will be bigger
+                        and we have to alter position
+                        '''
                         t_o_x = max(0, i * inv_scaling * view_tile_width) + scene_origin_x
                         t_o_y = max(0, j * inv_scaling * view_tile_height) + scene_origin_y
 
@@ -402,6 +409,7 @@ class ScenePyramid:
 
             # scale lower resolution tiles up (on slice > 0)
             inv_scale_factor = (1 / self.scalingFactor) ** self.currentSlice
+            assert inv_scale_factor >= 1
             item.setScale(inv_scale_factor)
 
             # and adjust position of tile accordingly
@@ -409,6 +417,7 @@ class ScenePyramid:
             y += j * (inv_scale_factor - 1) * int(self.tileDim[self.npHeightIdx])
 
             item.setPos(x, y)
+            item.setZValue(-1)
 
             item.setAcceptedMouseButtons(QtCore.Qt.NoButton)
             height, width, channel = img.shape
@@ -460,6 +469,7 @@ class ScenePyramid:
                     if i in pyramid_params:
                         setattr(self, i, pyramid_params[i])
 
+                self.fixTileDimensions()
                 self.tileWorkingSets = copy.deepcopy(self.tileSets)
                 self.fixMissingTiles()
 
@@ -717,7 +727,7 @@ class ScenePyramid:
         warnings.simplefilter('always', Image.DecompressionBombError)
         warnings.simplefilter('always', Image.DecompressionBombWarning)
 
-        p['preScanModeComplete'] = True
+        p['scanModeComplete'] = True
         p['fullImageWidth'] = img.width
         p['fullImageHeight'] = img.height
 
@@ -929,6 +939,27 @@ class ScenePyramid:
 
             scaling *= self.scalingFactor
 
+
+    def fixTileDimensions(self):
+        for s in self.tileSets:
+            for i in self.tileSets[s]:
+                for j in self.tileSets[s][i]:
+                    # as full image size might not be divisible by tile dimensions, we have to determine correct tile size
+                    # tile numbering is 0 based
+                    scaling = self.scalingFactor ** s
+                    max_y, max_x = self.tileDim
+                    fiw = scaling * self.fullImageWidth
+                    fih = scaling * self.fullImageHeight
+
+                    tile_w = int(math.ceil(max(min(max_x, fiw - i * max_x), 0)))
+                    tile_h = int(math.ceil(max(min(max_y, fih - j * max_y), 0)))
+
+                    is_dim = self.tileSets[s][i][j]['dimensions']
+                    should_dim = (tile_w, tile_h)
+                    if is_dim != should_dim:
+                        self.tileSets[s][i][j]['dimensions'] = should_dim
+
+
     def destruct(self):
         """
         removes all graphics items from scene