diff --git a/data/extensions/aseprite-theme/sheet.png b/data/extensions/aseprite-theme/sheet.png
index bc08c417e..4e3f1630d 100644
Binary files a/data/extensions/aseprite-theme/sheet.png and b/data/extensions/aseprite-theme/sheet.png differ
diff --git a/data/extensions/aseprite-theme/theme.xml b/data/extensions/aseprite-theme/theme.xml
index f27eef9c5..c3dabae98 100644
--- a/data/extensions/aseprite-theme/theme.xml
+++ b/data/extensions/aseprite-theme/theme.xml
@@ -418,6 +418,10 @@
         <part id="outline_vertical" x="192" y="224" w="13" h="15" />
         <part id="outline_empty_pixel" x="208" y="224" w="5" h="5" />
         <part id="outline_full_pixel" x="214" y="224" w="5" h="5" />
+        <part id="tiles" x="144" y="208" w="6" h="6" />
+        <part id="tiles_manual" x="150" y="208" w="6" h="6" />
+        <part id="tiles_semi" x="156" y="208" w="6" h="6" />
+        <part id="tiles_auto" x="162" y="208" w="6" h="6" />
     </parts>
     <styles>
         <style id="box" />
diff --git a/src/app/CMakeLists.txt b/src/app/CMakeLists.txt
index e94a21ad5..b98ecb540 100644
--- a/src/app/CMakeLists.txt
+++ b/src/app/CMakeLists.txt
@@ -447,6 +447,7 @@ add_library(app-lib
   cmd/move_layer.cpp
   cmd/patch_cel.cpp
   cmd/remap_colors.cpp
+  cmd/remap_tiles.cpp
   cmd/remove_cel.cpp
   cmd/remove_frame.cpp
   cmd/remove_layer.cpp
diff --git a/src/app/cmd/add_tile.cpp b/src/app/cmd/add_tile.cpp
index 22ba04ad7..1556d637e 100644
--- a/src/app/cmd/add_tile.cpp
+++ b/src/app/cmd/add_tile.cpp
@@ -25,7 +25,7 @@ AddTile::AddTile(doc::Tileset* tileset,
   : WithTileset(tileset)
   , WithImage(image.get())
   , m_size(0)
-  , m_tileIndex(-1)
+  , m_tileIndex(doc::tile_i_notile)
   , m_imageRef(image)
 {
 }
@@ -82,7 +82,10 @@ void AddTile::onRedo()
 
 void AddTile::addTile(doc::Tileset* tileset, const doc::ImageRef& image)
 {
-  m_tileIndex = tileset->add(image);
+  if (m_tileIndex == doc::tile_i_notile)
+    m_tileIndex = tileset->add(image);
+  else
+    tileset->insert(m_tileIndex, image);
 
   tileset->sprite()->incrementVersion();
   tileset->incrementVersion();
diff --git a/src/app/cmd/remap_tiles.cpp b/src/app/cmd/remap_tiles.cpp
new file mode 100644
index 000000000..974942e4f
--- /dev/null
+++ b/src/app/cmd/remap_tiles.cpp
@@ -0,0 +1,62 @@
+// Aseprite
+// Copyright (C) 2019  Igara Studio S.A.
+//
+// This program is distributed under the terms of
+// the End-User License Agreement for Aseprite.
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "app/cmd/remap_tiles.h"
+
+#include "doc/cel.h"
+#include "doc/cels_range.h"
+#include "doc/image.h"
+#include "doc/layer.h"
+#include "doc/layer_tilemap.h"
+#include "doc/remap.h"
+#include "doc/sprite.h"
+#include "doc/tileset.h"
+
+namespace app {
+namespace cmd {
+
+using namespace doc;
+
+RemapTiles::RemapTiles(Tileset* tileset,
+                       const Remap& remap)
+  : WithTileset(tileset)
+  , m_remap(remap)
+{
+}
+
+void RemapTiles::onExecute()
+{
+  Tileset* tileset = this->tileset();
+  Sprite* spr = tileset->sprite();
+  spr->remapTilemaps(tileset, m_remap);
+  incrementVersions(tileset);
+}
+
+void RemapTiles::onUndo()
+{
+  Tileset* tileset = this->tileset();
+  Sprite* spr = tileset->sprite();
+  spr->remapTilemaps(tileset, m_remap.invert());
+  incrementVersions(tileset);
+}
+
+void RemapTiles::incrementVersions(Tileset* tileset)
+{
+  Sprite* spr = tileset->sprite();
+  for (const Cel* cel : spr->uniqueCels()) {
+    if (cel->layer()->isTilemap() &&
+        static_cast<LayerTilemap*>(cel->layer())->tileset() == tileset) {
+      cel->image()->incrementVersion();
+    }
+  }
+}
+
+} // namespace cmd
+} // namespace app
diff --git a/src/app/cmd/remap_tiles.h b/src/app/cmd/remap_tiles.h
new file mode 100644
index 000000000..4cf81108a
--- /dev/null
+++ b/src/app/cmd/remap_tiles.h
@@ -0,0 +1,41 @@
+// Aseprite
+// Copyright (C) 2019  Igara Studio S.A.
+//
+// This program is distributed under the terms of
+// the End-User License Agreement for Aseprite.
+
+#ifndef APP_CMD_REMAP_TILES_H_INCLUDED
+#define APP_CMD_REMAP_TILES_H_INCLUDED
+#pragma once
+
+#include "app/cmd.h"
+#include "app/cmd/with_tileset.h"
+#include "doc/remap.h"
+
+namespace app {
+namespace cmd {
+  using namespace doc;
+
+  class RemapTiles : public Cmd
+                   , public WithTileset {
+  public:
+    RemapTiles(Tileset* tileset,
+               const Remap& remap);
+
+  protected:
+    void onExecute() override;
+    void onUndo() override;
+    size_t onMemSize() const override {
+      return sizeof(*this) + m_remap.getMemSize();
+    }
+
+  private:
+    void incrementVersions(Tileset* tileset);
+
+    Remap m_remap;
+  };
+
+} // namespace cmd
+} // namespace app
+
+#endif
diff --git a/src/app/cmd/trim_cel.cpp b/src/app/cmd/trim_cel.cpp
index 8fe15e5b0..1382f644b 100644
--- a/src/app/cmd/trim_cel.cpp
+++ b/src/app/cmd/trim_cel.cpp
@@ -1,4 +1,5 @@
 // Aseprite
+// Copyright (C) 2019  Igara Studio S.A.
 // Copyright (C) 2016  David Capello
 //
 // This program is distributed under the terms of
@@ -29,7 +30,7 @@ TrimCel::TrimCel(Cel* cel)
                                cel->image()->maskColor(),
                                cel->layer(), newBounds)) {
     newBounds.offset(cel->position());
-    if (cel->bounds() != newBounds) {
+    if (cel->imageBounds() != newBounds) {
       add(new cmd::CropCel(cel, newBounds));
     }
   }
diff --git a/src/app/script/engine.cpp b/src/app/script/engine.cpp
index c54c47480..413697378 100644
--- a/src/app/script/engine.cpp
+++ b/src/app/script/engine.cpp
@@ -349,9 +349,9 @@ Engine::Engine()
   lua_newtable(L);
   lua_pushvalue(L, -1);
   lua_setglobal(L, "TilesetMode");
-  setfield_integer(L, "LOCKED", TilesetMode::Locked);
-  setfield_integer(L, "MODIFY_EXISTENT", TilesetMode::ModifyExistent);
-  setfield_integer(L, "GENERATE_ALL_TILES", TilesetMode::GenerateAllTiles);
+  setfield_integer(L, "MANUAL", TilesetMode::Manual);
+  setfield_integer(L, "SEMI", TilesetMode::Semi);
+  setfield_integer(L, "AUTO", TilesetMode::Auto);
   lua_pop(L, 1);
 
   // Register classes/prototypes
diff --git a/src/app/site.h b/src/app/site.h
index 9b9ebf9e0..5047f92db 100644
--- a/src/app/site.h
+++ b/src/app/site.h
@@ -52,7 +52,7 @@ namespace app {
       , m_sprite(nullptr)
       , m_layer(nullptr)
       , m_frame(0)
-      , m_tilesetMode(TilesetMode::Locked) { }
+      , m_tilesetMode(TilesetMode::Manual) { }
 
     const Focus focus() const { return m_focus; }
     bool inEditor() const { return m_focus == InEditor; }
diff --git a/src/app/tileset_mode.h b/src/app/tileset_mode.h
index 54c73882d..2d0e8867a 100644
--- a/src/app/tileset_mode.h
+++ b/src/app/tileset_mode.h
@@ -13,10 +13,9 @@ namespace app {
   // These modes are available edition modes for the tileset when an
   // tilemap is edited.
   enum class TilesetMode {
-    Locked,           // Cannot edit the tileset (don't modify or add new tiles)
-    ModifyExistent,   // Modify existent tiles (don't create new ones)
-    //GenerateNewTiles, // Auto-generate new tiles, edit existent ones
-    GenerateAllTiles, // Auto-generate new and modified tiles
+    Manual,   // Modify existent tiles (don't create new ones)
+    Semi,     // Auto-generate new tiles if needed, edit existent ones
+    Auto,     // Auto-generate new and modified tiles
   };
 
 } // namespace app
diff --git a/src/app/ui/color_bar.cpp b/src/app/ui/color_bar.cpp
index fd9e288a2..1acd03ce3 100644
--- a/src/app/ui/color_bar.cpp
+++ b/src/app/ui/color_bar.cpp
@@ -88,12 +88,6 @@ enum class PalButton {
   MAX
 };
 
-enum class TilesButton {
-  MODE,
-  AUTO,
-  MAX
-};
-
 using namespace app::skin;
 using namespace ui;
 
@@ -147,7 +141,8 @@ ColorBar* ColorBar::m_instance = NULL;
 ColorBar::ColorBar(int align, TooltipManager* tooltipManager)
   : Box(align)
   , m_buttons(int(PalButton::MAX))
-  , m_tilesButtons(int(TilesButton::MAX))
+  , m_tilesButton(1)
+  , m_tilesetModeButtons(3)
   , m_splitter(Splitter::ByPercentage, VERTICAL)
   , m_paletteView(true, PaletteView::FgBgColors, this, 16)
   , m_tilesView(true, PaletteView::FgBgTiles, this, 16)
@@ -170,7 +165,7 @@ ColorBar::ColorBar(int align, TooltipManager* tooltipManager)
   , m_lastButtons(kButtonLeft)
   , m_editMode(false)
   , m_tilesMode(false)
-  , m_autoTilesMode(true)
+  , m_tilesetMode(TilesetMode::Semi)
   , m_redrawTimer(250, this)
   , m_redrawAll(false)
   , m_implantChange(false)
@@ -185,10 +180,12 @@ ColorBar::ColorBar(int align, TooltipManager* tooltipManager)
   m_buttons.addItem(theme->parts.palPresets());
   m_buttons.addItem(theme->parts.palOptions());
 
-  m_tilesButtons.addItem("Tiles");
-  m_tilesButtons.addItem("Auto");
-  m_tilesButtons.setVisible(false);
-  m_tilesButtons.getItem((int)TilesButton::AUTO)->setHotColor(theme->colors.editPalFace());
+  m_tilesButton.addItem(theme->parts.tiles());
+
+  m_tilesetModeButtons.addItem(theme->parts.tilesManual());
+  m_tilesetModeButtons.addItem(theme->parts.tilesSemi());
+  m_tilesetModeButtons.addItem(theme->parts.tilesAuto());
+  setTilesetMode(m_tilesetMode);
 
   m_paletteView.setColumns(8);
   m_tilesView.setColumns(8);
@@ -213,8 +210,11 @@ ColorBar::ColorBar(int align, TooltipManager* tooltipManager)
   setColorSelector(
     Preferences::instance().colorBar.selector());
 
+  m_tilesHBox.addChild(&m_tilesButton);
+  m_tilesHBox.addChild(&m_tilesetModeButtons);
+
   addChild(&m_buttons);
-  addChild(&m_tilesButtons);
+  addChild(&m_tilesHBox);
   addChild(&m_splitter);
 
   HBox* fgBox = new HBox;
@@ -239,7 +239,8 @@ ColorBar::ColorBar(int align, TooltipManager* tooltipManager)
   m_bgWarningIcon->Click.connect(base::Bind<void>(&ColorBar::onFixWarningClick, this, &m_bgColor, m_bgWarningIcon));
   m_redrawTimer.Tick.connect(base::Bind<void>(&ColorBar::onTimerTick, this));
   m_buttons.ItemChange.connect(base::Bind<void>(&ColorBar::onPaletteButtonClick, this));
-  m_tilesButtons.ItemChange.connect(base::Bind<void>(&ColorBar::onTilesButtonClick, this));
+  m_tilesButton.ItemChange.connect(base::Bind<void>(&ColorBar::onTilesButtonClick, this));
+  m_tilesetModeButtons.ItemChange.connect(base::Bind<void>(&ColorBar::onTilesetModeButtonClick, this));
 
   tooltipManager->addTooltipFor(&m_fgColor, "Foreground color", LEFT);
   tooltipManager->addTooltipFor(&m_bgColor, "Background color", LEFT);
@@ -257,11 +258,14 @@ ColorBar::ColorBar(int align, TooltipManager* tooltipManager)
       m_bgColor.resetSizeHint();
       m_fgColor.setSizeHint(0, m_fgColor.sizeHint().h);
       m_bgColor.setSizeHint(0, m_bgColor.sizeHint().h);
-      m_buttons.setMinSize(gfx::Size(0, theme->dimensions.colorBarButtonsHeight()));
-      m_buttons.setMaxSize(gfx::Size(std::numeric_limits<int>::max(),
-                                     std::numeric_limits<int>::max())); // TODO add resetMaxSize
-      m_buttons.setMaxSize(gfx::Size(m_buttons.sizeHint().w,
-                                     theme->dimensions.colorBarButtonsHeight()));
+
+      for (auto w : { &m_buttons, &m_tilesButton, &m_tilesetModeButtons }) {
+        w->setMinSize(gfx::Size(0, theme->dimensions.colorBarButtonsHeight()));
+        w->setMaxSize(gfx::Size(std::numeric_limits<int>::max(),
+                                std::numeric_limits<int>::max())); // TODO add resetMaxSize
+        w->setMaxSize(gfx::Size(m_buttons.sizeHint().w,
+                                theme->dimensions.colorBarButtonsHeight()));
+      }
 
       // Change color-bar background color (not ColorBar::setBgColor)
       this->Widget::setBgColor(theme->colors.tabActiveFace());
@@ -444,8 +448,7 @@ void ColorBar::setEditMode(bool state)
   m_editMode = state;
   item->setIcon(state ? theme->parts.timelineOpenPadlockActive():
                         theme->parts.timelineClosedPadlockNormal());
-  item->setHotColor(state ? theme->colors.editPalFace():
-                            gfx::ColorNone);
+  item->setHotColor(state ? theme->colors.editPalFace(): gfx::ColorNone);
 
   // Deselect color entries when we cancel editing
   if (!state)
@@ -456,7 +459,7 @@ bool ColorBar::inTilesMode() const
 {
   return
     (m_tilesMode &&
-     m_tilesButtons.isVisible() &&
+     m_tilesHBox.isVisible() &&
      m_lastDocument &&
      m_lastDocument->sprite());
 }
@@ -467,10 +470,11 @@ void ColorBar::setTilesMode(bool state)
   const bool isTilemap = (site.layer() && site.layer()->isTilemap());
 
   SkinTheme* theme = static_cast<SkinTheme*>(this->theme());
-  ButtonSet::Item* item = m_tilesButtons.getItem((int)TilesButton::MODE);
+  ButtonSet::Item* item = m_tilesButton.getItem(0);
 
   m_tilesMode = state;
   item->setHotColor(state ? theme->colors.editPalFace(): gfx::ColorNone);
+  item->setMono(true);
 
   if (state && isTilemap) {
     manager()->freeWidget(&m_paletteView);
@@ -486,30 +490,25 @@ void ColorBar::setTilesMode(bool state)
   layout();
 }
 
-bool ColorBar::inAutoTilesMode() const
-{
-  return
-    (m_autoTilesMode &&
-     m_tilesButtons.isVisible() &&
-     m_lastDocument &&
-     m_lastDocument->sprite());
-}
-
-void ColorBar::setAutoTilesMode(bool state)
-{
-  SkinTheme* theme = static_cast<SkinTheme*>(this->theme());
-  ButtonSet::Item* item = m_tilesButtons.getItem((int)TilesButton::AUTO);
-
-  m_autoTilesMode = state;
-  item->setHotColor(state ? theme->colors.editPalFace(): gfx::ColorNone);
-}
-
 TilesetMode ColorBar::tilesetMode() const
 {
-  if (inAutoTilesMode())
-    return TilesetMode::GenerateAllTiles;
+  if (m_tilesHBox.isVisible() &&
+      m_lastDocument &&
+      m_lastDocument->sprite()) {
+    return m_tilesetMode;
+  }
   else
-    return TilesetMode::ModifyExistent;
+    return TilesetMode::Manual;
+}
+
+void ColorBar::setTilesetMode(const TilesetMode mode)
+{
+  m_tilesetMode = mode;
+
+  for (int i=0; i<3; ++i) {
+    ButtonSet::Item* item = m_tilesetModeButtons.getItem(i);
+    item->setSelected(int(mode) == i);
+  }
 }
 
 void ColorBar::onActiveSiteChange(const Site& site)
@@ -527,20 +526,20 @@ void ColorBar::onActiveSiteChange(const Site& site)
   }
 
   bool isTilemap = false;
-  if (site.layer()) {
+  if (site.layer())
     isTilemap = site.layer()->isTilemap();
-    if (m_tilesButtons.isVisible() != isTilemap) {
-      m_tilesButtons.setVisible(isTilemap);
-      layout();
-    }
 
-    if (isTilemap) {
-      doc::ObjectId newTilesetId =
-        static_cast<const doc::LayerTilemap*>(site.layer())->tileset()->id();
-      if (m_lastTilesetId != newTilesetId) {
-        m_lastTilesetId = newTilesetId;
-        m_scrollableTilesView.updateView();
-      }
+  if (m_tilesHBox.isVisible() != isTilemap) {
+    m_tilesHBox.setVisible(isTilemap);
+    layout();
+  }
+
+  if (isTilemap) {
+    doc::ObjectId newTilesetId =
+      static_cast<const doc::LayerTilemap*>(site.layer())->tileset()->id();
+    if (m_lastTilesetId != newTilesetId) {
+      m_lastTilesetId = newTilesetId;
+      m_scrollableTilesView.updateView();
     }
   }
   if (!isTilemap) {
@@ -563,7 +562,6 @@ void ColorBar::onTilesetChanged(DocEvent& ev)
   if (!ui::is_ui_thread())
     return;
 
-  m_tilesButtons.deselectItems();
   if (m_scrollableTilesView.isVisible())
     m_scrollableTilesView.updateView();
 
@@ -639,20 +637,15 @@ void ColorBar::onPaletteButtonClick()
 
 void ColorBar::onTilesButtonClick()
 {
-  int item = m_tilesButtons.selectedItem();
-  m_tilesButtons.deselectItems();
+  m_tilesButton.deselectItems();
+  setTilesMode(!inTilesMode());
+}
 
-  switch (static_cast<TilesButton>(item)) {
-
-    case TilesButton::MODE:
-      setTilesMode(!inTilesMode());
-      break;
-
-    case TilesButton::AUTO:
-      setAutoTilesMode(!inAutoTilesMode());
-      break;
-
-  }
+void ColorBar::onTilesetModeButtonClick()
+{
+  int item = m_tilesetModeButtons.selectedItem();
+  m_tilesetModeButtons.deselectItems();
+  setTilesetMode(static_cast<TilesetMode>(item));
 }
 
 void ColorBar::onRemapButtonClick()
@@ -1398,9 +1391,13 @@ void ColorBar::setupTooltips(TooltipManager* tooltipManager)
   tooltipManager->addTooltipFor(&m_remapButton, "Matches old indexes with new indexes", BOTTOM);
 
   tooltipManager->addTooltipFor(
-    m_tilesButtons.getItem((int)TilesButton::MODE), "Show Tileset", BOTTOM);
+    m_tilesButton.getItem(0), "Show/Hide Tileset", BOTTOM);
   tooltipManager->addTooltipFor(
-    m_tilesButtons.getItem((int)TilesButton::AUTO), "Generate new tiles automatically", BOTTOM);
+    m_tilesetModeButtons.getItem((int)TilesetMode::Manual), "Manual-mode: Modify existent tiles,\ndon't create new tiles automatically", BOTTOM);
+  tooltipManager->addTooltipFor(
+    m_tilesetModeButtons.getItem((int)TilesetMode::Semi), "Semi-mode: Modify and reuse existent tiles,\ncreate/delete tiles if needed/possible", BOTTOM);
+  tooltipManager->addTooltipFor(
+    m_tilesetModeButtons.getItem((int)TilesetMode::Auto), "Auto-mode: Don't modify existent tiles,\ngenerate new tiles automatically only", BOTTOM);
 }
 
 // static
diff --git a/src/app/ui/color_bar.h b/src/app/ui/color_bar.h
index 5b0f71dc9..a547f79d0 100644
--- a/src/app/ui/color_bar.h
+++ b/src/app/ui/color_bar.h
@@ -83,10 +83,8 @@ namespace app {
     bool inTilesMode() const;
     void setTilesMode(bool state);
 
-    bool inAutoTilesMode() const;
-    void setAutoTilesMode(bool state);
-
     TilesetMode tilesetMode() const;
+    void setTilesetMode(const TilesetMode mode);
 
     ColorButton* fgColorButton() { return &m_fgColor; }
     ColorButton* bgColorButton() { return &m_bgColor; }
@@ -120,6 +118,7 @@ namespace app {
     void onAfterExecuteCommand(CommandExecutionEvent& ev);
     void onPaletteButtonClick();
     void onTilesButtonClick();
+    void onTilesetModeButtonClick();
     void onRemapButtonClick();
     void onPaletteIndexChange(PaletteIndexChangeEvent& ev);
     void onFgColorChangeFromPreferences();
@@ -170,7 +169,9 @@ namespace app {
     class WarningIcon;
 
     ButtonSet m_buttons;
-    ButtonSet m_tilesButtons;
+    ui::HBox m_tilesHBox;
+    ButtonSet m_tilesButton;
+    ButtonSet m_tilesetModeButtons;
     std::unique_ptr<PalettePopup> m_palettePopup;
     ui::Splitter m_splitter;
     ui::VBox m_palettePlaceholder;
@@ -217,7 +218,7 @@ namespace app {
 
     // True if we should be putting/setting tiles.
     bool m_tilesMode;
-    bool m_autoTilesMode;
+    TilesetMode m_tilesetMode;
 
     // Timer to redraw editors after a palette change.
     ui::Timer m_redrawTimer;
diff --git a/src/app/ui/palette_view.cpp b/src/app/ui/palette_view.cpp
index e0e53824b..a907e102c 100644
--- a/src/app/ui/palette_view.cpp
+++ b/src/app/ui/palette_view.cpp
@@ -766,8 +766,12 @@ void PaletteView::onPaint(ui::PaintEvent& ev)
 
   const int size = m_adapter->size();
   for (int i=0; i<size; ++i) {
-    if (!m_selectedEntries[i])
+    // TODO why does this fail?
+    //ASSERT(i >= 0 && i < m_selectedEntries.size());
+    if (i >= 0 && i < m_selectedEntries.size() &&
+        !m_selectedEntries[i]) {
       continue;
+    }
 
     const int k = (dragging ? m_hot.color+j: i);
 
diff --git a/src/app/util/cel_ops.cpp b/src/app/util/cel_ops.cpp
index 6f9b5bed1..21314711e 100644
--- a/src/app/util/cel_ops.cpp
+++ b/src/app/util/cel_ops.cpp
@@ -15,6 +15,8 @@
 #include "app/cmd/clear_cel.h"
 #include "app/cmd/clear_mask.h"
 #include "app/cmd/copy_region.h"
+#include "app/cmd/remap_tiles.h"
+#include "app/cmd/remove_tile.h"
 #include "app/cmd/replace_image.h"
 #include "app/cmd/set_cel_position.h"
 #include "app/cmd_sequence.h"
@@ -40,6 +42,7 @@
 #include "render/quantization.h"
 #include "render/render.h"
 
+#include <algorithm>
 #include <cmath>
 #include <memory>
 
@@ -403,7 +406,8 @@ void modify_tilemap_cel_region(
             newTilemapBounds.x, newTilemapBounds.y, newTilemapBounds.w, newTilemapBounds.h);
 
   // Autogenerate tiles
-  if (tilesetMode == TilesetMode::GenerateAllTiles) {
+  if (tilesetMode == TilesetMode::Auto ||
+      tilesetMode == TilesetMode::Semi) {
     doc::TilesetHashTable hashImages; // TODO the hashImages should be inside the Tileset
     {
       // Add existent tiles in the hash table
@@ -434,6 +438,8 @@ void modify_tilemap_cel_region(
     regionToPatch -= gfx::Region(grid.tileToCanvas(oldTilemapBounds));
     regionToPatch |= region;
 
+    std::vector<bool> modifiedTileIndexes(tileset->size(), false);
+
     for (const gfx::Point& tilePt : grid.tilesInCanvasRegion(regionToPatch)) {
       const int u = tilePt.x-newTilemapBounds.x;
       const int v = tilePt.y-newTilemapBounds.y;
@@ -445,6 +451,9 @@ void modify_tilemap_cel_region(
       const doc::tile_index ti = doc::tile_geti(t);
       const doc::ImageRef existenTileImage = tileset->get(ti);
 
+      if (tilesetMode == TilesetMode::Semi)
+        modifiedTileIndexes[ti] = true;
+
       const gfx::Rect tileInCanvasRc(grid.tileToCanvas(tilePt), tileSize);
       ImageRef tileImage(getTileImage(existenTileImage, tileInCanvasRc));
       if (grid.hasMask())
@@ -455,6 +464,9 @@ void modify_tilemap_cel_region(
       auto it = hashImages.find(tileImage);
       if (it != hashImages.end()) {
         tileIndex = it->second; // TODO
+
+        if (tilesetMode == TilesetMode::Semi)
+          modifiedTileIndexes[tileIndex] = false;
       }
       else {
         auto addTile = new cmd::AddTile(tileset, tileImage);
@@ -464,6 +476,8 @@ void modify_tilemap_cel_region(
         hashImages[tileImage] = tileIndex;
       }
 
+      OPS_TRACE(" - tile %d -> %d\n", ti, tileIndex);
+
       const doc::tile_t tile = doc::tile(tileIndex, 0);
       if (t != tile) {
         newTilemap->putPixel(u, v, tile);
@@ -471,8 +485,6 @@ void modify_tilemap_cel_region(
       }
     }
 
-    doc->notifyTilesetChanged(tileset);
-
     if (newTilemap->width() != cel->image()->width() ||
         newTilemap->height() != cel->image()->height()) {
       gfx::Point newPos = grid.tileToCanvas(newTilemapBounds.origin());
@@ -491,9 +503,17 @@ void modify_tilemap_cel_region(
           tilePtsRgn,
           gfx::Point(0, 0)));
     }
+
+    // Remove unused tiles
+    if (tilesetMode == TilesetMode::Semi) {
+      // TODO reuse tiles that will be removed in the algorithm above
+      remove_unused_tiles_from_tileset(cmds, tileset, modifiedTileIndexes);
+    }
+
+    doc->notifyTilesetChanged(tileset);
   }
   // Modify active set of tiles manually / don't auto-generate new tiles
-  else if (tilesetMode == TilesetMode::ModifyExistent) {
+  else if (tilesetMode == TilesetMode::Manual) {
     for (const gfx::Point& tilePt : grid.tilesInCanvasRegion(region)) {
       // Ignore modifications outside the tilemap
       if (!cel->image()->bounds().contains(tilePt.x, tilePt.y))
@@ -567,4 +587,59 @@ void clear_mask_from_cel(CmdSequence* cmds,
   }
 }
 
+void remove_unused_tiles_from_tileset(
+  CmdSequence* cmds,
+  doc::Tileset* tileset,
+  std::vector<bool>& unusedTiles)
+{
+  OPS_TRACE("remove_unused_tiles_from_tileset\n");
+
+  int n = tileset->size();
+
+  for (Cel* cel : tileset->sprite()->cels()) {
+    if (!cel->layer()->isTilemap() ||
+        static_cast<LayerTilemap*>(cel->layer())->tileset() != tileset)
+      continue;
+
+    Image* tilemapImage = cel->image();
+    for_each_pixel<TilemapTraits>(
+      tilemapImage,
+      [&unusedTiles, &n](const doc::tile_t t) {
+        const doc::tile_index ti = doc::tile_geti(t);
+        n = std::max<int>(n, ti+1);
+        if (ti >= 0 &&
+            ti < int(unusedTiles.size()) &&
+            unusedTiles[ti]) {
+          unusedTiles[ti] = false;
+        }
+      });
+  }
+
+  doc::Remap remap(n);
+  doc::tile_index ti, tj;
+  ti = tj = 0;
+  for (; ti<remap.size(); ++ti) {
+    OPS_TRACE(" - ti=%d tj=%d unusedTiles[%d]=%d\n",
+              ti, tj, ti, (ti < unusedTiles.size() && unusedTiles[ti] ? 1: 0));
+    if (ti < unusedTiles.size() &&
+        unusedTiles[ti]) {
+      cmds->executeAndAdd(new cmd::RemoveTile(tileset, tj));
+      // Map to nothing, so the map can be invertible
+      remap.map(ti, doc::Remap::kNoMap);
+    }
+    else {
+      remap.map(ti, tj++);
+    }
+  }
+
+  if (!remap.isIdentity()) {
+#ifdef _DEBUG
+    for (ti=0; ti<remap.size(); ++ti) {
+      OPS_TRACE(" - remap tile[%d] -> %d\n", ti, remap[ti]);
+    }
+#endif
+    cmds->executeAndAdd(new cmd::RemapTiles(tileset, remap));
+  }
+}
+
 } // namespace app
diff --git a/src/app/util/cel_ops.h b/src/app/util/cel_ops.h
index e4568c1fe..d6d6e0993 100644
--- a/src/app/util/cel_ops.h
+++ b/src/app/util/cel_ops.h
@@ -17,12 +17,14 @@
 #include "gfx/region.h"
 
 #include <functional>
+#include <vector>
 
 namespace doc {
   class Cel;
   class Layer;
   class LayerTilemap;
   class Sprite;
+  class Tileset;
 }
 
 namespace app {
@@ -68,6 +70,13 @@ namespace app {
     doc::Cel* cel,
     const TilesetMode tilesetMode);
 
+  // unusedTiles is a set of possibles tiles to check if they are
+  // really unused by all tilemaps.
+  void remove_unused_tiles_from_tileset(
+    CmdSequence* cmds,
+    doc::Tileset* tileset,
+    std::vector<bool>& unusedTiles);
+
 } // namespace app
 
 #endif
diff --git a/src/doc/cel.h b/src/doc/cel.h
index 7fddbcc0d..6cb8b3f17 100644
--- a/src/doc/cel.h
+++ b/src/doc/cel.h
@@ -39,6 +39,8 @@ namespace doc {
     const gfx::RectF& boundsF() const { return m_data->boundsF(); }
     int opacity() const { return m_data->opacity(); }
 
+    gfx::Rect imageBounds() const { return m_data->imageBounds(); }
+
     LayerImage* layer() const { return m_layer; }
     Image* image() const { return m_data->image(); }
     ImageRef imageRef() const { return m_data->imageRef(); }
diff --git a/src/doc/cel_data.h b/src/doc/cel_data.h
index 8e535e7b4..1cb37f143 100644
--- a/src/doc/cel_data.h
+++ b/src/doc/cel_data.h
@@ -33,6 +33,17 @@ namespace doc {
     Image* image() const { return const_cast<Image*>(m_image.get()); };
     ImageRef imageRef() const { return m_image; }
 
+    // Returns a rectangle with the bounds of the image (width/height
+    // of the image) in the position of the cel (useful to compare
+    // active tilemap bounds when we have to change the tilemap cel
+    // bounds).
+    gfx::Rect imageBounds() const {
+      return gfx::Rect(m_bounds.x,
+                       m_bounds.y,
+                       m_image->width(),
+                       m_image->height());
+    }
+
     void setImage(const ImageRef& image, Layer* layer);
     void setPosition(const gfx::Point& pos);
     void setOpacity(int opacity) { m_opacity = opacity; }
diff --git a/src/doc/image_bits.h b/src/doc/image_bits.h
index 7ef714fc5..85c72801f 100644
--- a/src/doc/image_bits.h
+++ b/src/doc/image_bits.h
@@ -1,5 +1,6 @@
 // Aseprite Document Library
-// Copyright (c) 2001-2014 David Capello
+// Copyright (C) 2019  Igara Studio S.A.
+// Copyright (C) 2001-2014  David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -8,6 +9,8 @@
 #define DOC_IMAGE_BITS_H_INCLUDED
 #pragma once
 
+#include <algorithm>
+
 namespace doc {
 
   class Image;
@@ -152,6 +155,20 @@ namespace doc {
     LockImageBits();            // Undefined
   };
 
+  template<class ImageTraits,
+           class UnaryFunction>
+  inline void for_each_pixel(const Image* image, UnaryFunction f) {
+    const LockImageBits<ImageTraits> bits(image);
+    std::for_each(bits.begin(), bits.end(), f);
+  }
+
+  template<class ImageTraits,
+           class UnaryOperation>
+  inline void transform_image(Image* image, UnaryOperation f) {
+    LockImageBits<ImageTraits> bits(image);
+    std::transform(bits.begin(), bits.end(), bits.begin(), f);
+  }
+
 } // namespace doc
 
 #endif
diff --git a/src/doc/primitives.cpp b/src/doc/primitives.cpp
index cf9ce05e2..372a35f8c 100644
--- a/src/doc/primitives.cpp
+++ b/src/doc/primitives.cpp
@@ -413,17 +413,24 @@ bool is_same_image(const Image* i1, const Image* i2)
 
 void remap_image(Image* image, const Remap& remap)
 {
-  ASSERT(image->pixelFormat() == IMAGE_INDEXED);
-  if (image->pixelFormat() != IMAGE_INDEXED)
-    return;
+  ASSERT(image->pixelFormat() == IMAGE_INDEXED ||
+         image->pixelFormat() == IMAGE_TILEMAP);
 
-  LockImageBits<IndexedTraits> bits(image);
-  LockImageBits<IndexedTraits>::iterator
-    it = bits.begin(),
-    end = bits.end();
-
-  for (; it != end; ++it)
-    *it = remap[*it];
+  switch (image->pixelFormat()) {
+    case IMAGE_INDEXED:
+      transform_image<IndexedTraits>(
+        image, [&remap](color_t c) -> color_t {
+                 return remap[c];
+               });
+      break;
+    case IMAGE_TILEMAP:
+      transform_image<TilemapTraits>(
+        image, [&remap](color_t c) -> color_t {
+                 ASSERT(remap[c] != Remap::kNoMap);
+                 return remap[c];
+               });
+      break;
+  }
 }
 
 // TODO test this hash routine and find a better alternative
diff --git a/src/doc/remap.cpp b/src/doc/remap.cpp
index cbacc15d5..0857454f7 100644
--- a/src/doc/remap.cpp
+++ b/src/doc/remap.cpp
@@ -1,6 +1,6 @@
 // Aseprite Document Library
-// Copyright (c)      2020 Igara Studio S.A.
-// Copyright (c) 2001-2016 David Capello
+// Copyright (C) 2019-2020  Igara Studio S.A.
+// Copyright (C) 2001-2016  David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -135,8 +135,12 @@ void Remap::merge(const Remap& other)
 Remap Remap::invert() const
 {
   Remap inv(size());
-  for (int i=0; i<size(); ++i)
-    inv.map(operator[](i), i);
+  for (int i=0; i<size(); ++i) {
+    int j = m_map[i];
+    if (j == kNoMap)
+      continue;
+    inv.map(j, i);
+  }
   return inv;
 }
 
@@ -160,6 +164,9 @@ bool Remap::isInvertible(const PalettePicks& usedEntries) const
       continue;
 
     int j = m_map[i];
+    if (j == kNoMap)
+      continue;
+
     if (picks[j])
       return false;
 
@@ -168,4 +175,13 @@ bool Remap::isInvertible(const PalettePicks& usedEntries) const
   return true;
 }
 
+bool Remap::isIdentity() const
+{
+  for (int i=0; i<size(); ++i) {
+    if (m_map[i] != i)
+      return false;
+  }
+  return true;
+}
+
 } // namespace doc
diff --git a/src/doc/remap.h b/src/doc/remap.h
index e0f362543..1586183d0 100644
--- a/src/doc/remap.h
+++ b/src/doc/remap.h
@@ -1,5 +1,6 @@
 // Aseprite Document Library
-// Copyright (c) 2001-2017 David Capello
+// Copyright (C) 2019  Igara Studio S.A.
+// Copyright (C) 2001-2017  David Capello
 //
 // This file is released under the terms of the MIT license.
 // Read LICENSE.txt for more information.
@@ -18,6 +19,8 @@ namespace doc {
 
   class Remap {
   public:
+    static const int kNoMap = -1;
+
     Remap(int entries = 1) : m_map(entries, 0) { }
 
     int size() const {
@@ -27,7 +30,10 @@ namespace doc {
     // Maps input "fromIndex" value, to "toIndex" output.
     void map(int fromIndex, int toIndex) {
       ASSERT(fromIndex >= 0 && fromIndex < size());
-      ASSERT(toIndex >= 0 && toIndex < size());
+      // toIndex = kNoMap means (there is no remap for this value, useful
+      // to ignore this entry when we invert the map)
+      ASSERT(toIndex == kNoMap ||
+             toIndex >= 0 && toIndex < size());
 
       m_map[fromIndex] = toIndex;
     }
@@ -57,6 +63,10 @@ namespace doc {
     // undo data, without saving all images' pixels.
     bool isInvertible(const PalettePicks& usedEntries) const;
 
+    // Returns true if the remap does nothing (each map entry is
+    // matched to itself).
+    bool isIdentity() const;
+
   private:
     std::vector<int> m_map;
   };
diff --git a/src/doc/sprite.cpp b/src/doc/sprite.cpp
index c67d5823d..01f3a5f67 100644
--- a/src/doc/sprite.cpp
+++ b/src/doc/sprite.cpp
@@ -525,6 +525,17 @@ void Sprite::remapImages(const Remap& remap)
     remap_image(image.get(), remap);
 }
 
+void Sprite::remapTilemaps(const Tileset* tileset,
+                           const Remap& remap)
+{
+  for (Cel* cel : uniqueCels()) {
+    if (cel->layer()->isTilemap() &&
+        static_cast<LayerTilemap*>(cel->layer())->tileset() == tileset) {
+      remap_image(cel->image(), remap);
+    }
+  }
+}
+
 //////////////////////////////////////////////////////////////////////
 // Drawing
 
diff --git a/src/doc/sprite.h b/src/doc/sprite.h
index 97ea7bea8..3c6db2b19 100644
--- a/src/doc/sprite.h
+++ b/src/doc/sprite.h
@@ -43,6 +43,7 @@ namespace doc {
   class Remap;
   class RgbMap;
   class SelectedFrames;
+  class Tileset;
   class Tilesets;
 
   typedef std::vector<Palette*> PalettesList;
@@ -172,6 +173,8 @@ namespace doc {
     void getImages(std::vector<ImageRef>& images) const;
 
     void remapImages(const Remap& remap);
+    void remapTilemaps(const Tileset* tileset,
+                       const Remap& remap);
     void pickCels(const double x,
                   const double y,
                   const frame_t frame,
diff --git a/src/doc/tile.h b/src/doc/tile.h
index 0a128cf98..f44b64d89 100644
--- a/src/doc/tile.h
+++ b/src/doc/tile.h
@@ -20,6 +20,7 @@ namespace doc {
   const uint32_t tile_i_shift = 0;  // Tile index
   const uint32_t tile_f_shift = 28; // Flags (flip, rotation)
 
+  const uint32_t tile_i_notile = 0xffffffff;
   const uint32_t tile_i_mask  = 0x1fffffff;
   const uint32_t tile_f_mask  = 0xe0000000; // 3 flags
   const uint32_t tile_f_flipx = 0x20000000;
diff --git a/src/doc/tileset.h b/src/doc/tileset.h
index 713ed2c84..57c1267ec 100644
--- a/src/doc/tileset.h
+++ b/src/doc/tileset.h
@@ -43,16 +43,16 @@ namespace doc {
     tile_index size() const { return tile_index(m_tiles.size()); }
     void resize(const tile_index ntiles);
 
-    ImageRef get(const tile_index index) const {
-      if (index < size())
-        return m_tiles[index];
+    ImageRef get(const tile_index ti) const {
+      if (ti < size())
+        return m_tiles[ti];
       else
         return ImageRef(nullptr);
     }
 
-    void set(const tile_index index,
+    void set(const tile_index ti,
              const ImageRef& image) {
-      m_tiles[index] = image;
+      m_tiles[ti] = image;
     }
 
     tile_index add(const ImageRef& image) {
@@ -60,6 +60,12 @@ namespace doc {
       return tile_t(m_tiles.size()-1);
     }
 
+    void insert(const tile_index ti,
+                const ImageRef& image) {
+      ASSERT(ti <= size());
+      m_tiles.insert(m_tiles.begin()+ti, image);
+    }
+
     void erase(const tile_index ti) {
       ASSERT(ti >= 0 && ti < size());
       m_tiles.erase(m_tiles.begin()+ti);