diff --git a/src/buttons.c b/src/buttons.c
index d1cce56a..74f939b7 100644
--- a/src/buttons.c
+++ b/src/buttons.c
@@ -506,9 +506,8 @@ void Button_Toggle_toolbar(void)
 
   Window_dropdown_add_item(&dropdown, 0, menu_name_tools);
   
-  if (Main_backups->Pages->Image_mode == IMAGE_MODE_LAYERED ||
-      Main_backups->Pages->Image_mode == IMAGE_MODE_MODE5 ||
-    (Main_backups->Pages->Image_mode == IMAGE_MODE_ANIMATION && Main_backups->Pages->Nb_layers==1))
+  if (Main_backups->Pages->Image_mode != IMAGE_MODE_ANIMATION ||
+      Main_backups->Pages->Nb_layers==1)
     Window_dropdown_add_item(&dropdown, 1, menu_name_layers);
   
   if (Main_backups->Pages->Image_mode == IMAGE_MODE_ANIMATION ||
@@ -544,7 +543,7 @@ void Button_Toggle_toolbar(void)
         }
         Set_bar_visibility(MENUBAR_ANIMATION, !Menu_bars[MENUBAR_ANIMATION].Visible, 0);
 
-        if (Main_backups->Pages->Image_mode == IMAGE_MODE_LAYERED)
+        if (Main_backups->Pages->Image_mode != IMAGE_MODE_ANIMATION)
           Switch_layer_mode(IMAGE_MODE_ANIMATION);
         
         break;
@@ -4860,10 +4859,10 @@ void Button_Effects(void)
           Display_effect_state(C2,L4, "8 bit" ,Main_backups->Pages->Image_mode > IMAGE_MODE_ANIMATION);
           Display_cursor();
         } else {
-          //Close_window();
-          //Display_cursor();
-          // Contraint checker/enforcer menu
-          //clicked_button = 11;
+          Close_window();
+          Display_cursor();
+          Button_Constraint_menu();
+          clicked_button = 11;
         }
         break;
       case 15: // Tilemap
diff --git a/src/buttons_effects.c b/src/buttons_effects.c
index b9d6fab4..bcd6d873 100644
--- a/src/buttons_effects.c
+++ b/src/buttons_effects.c
@@ -3,7 +3,7 @@
 /*  Grafx2 - The Ultimate 256-color bitmap paint program
 
     Copyright 2008 Yves Rizoud
-    Copyright 2007 Adrien Destugues
+    Copyright 2007-2017 Adrien Destugues
     Copyright 1996-2001 Sunset Design (Guillaume Dorme & Karl Maritaud)
 
     Grafx2 is free software; you can redistribute it and/or
@@ -163,41 +163,84 @@ void Menu_tag_colors(char * window_title, byte * table, byte * mode, byte can_ca
   Display_cursor();
 }
 
+byte Selected_Constraint_Mode = 0;
 
 // Constaint enforcer/checker ------------------------------------------------
-void Button_Constraint_mode(void)
+void Button_Constraint_mode()
 {
   int pixel;
   
-  if (Main_backups->Pages->Image_mode == IMAGE_MODE_MODE5)
+  if (Main_backups->Pages->Image_mode >= IMAGE_MODE_MODE5)
   {
     // Disable
     Switch_layer_mode(IMAGE_MODE_LAYERED);
     return;
   }
-  if (Main_backups->Pages->Image_mode != IMAGE_MODE_LAYERED ||
-    Main_backups->Pages->Nb_layers!=5 || (Main_image_width%48))
+
+  if (Selected_Constraint_Mode < IMAGE_MODE_MODE5)
+    Selected_Constraint_Mode = IMAGE_MODE_EGX;
+
+  if (Selected_Constraint_Mode == IMAGE_MODE_MODE5)
   {
-    Verbose_message("Error!", "This emulation of Amstrad CPC's Mode5 can only be used on a 5-layer image whose width is a multiple of 48.");
-    return;
-  }
-  for (pixel=0; pixel < Main_image_width*Main_image_height; pixel++)
-  {
-    if (Main_backups->Pages->Image[4].Pixels[pixel]>3)
+    if (Main_backups->Pages->Image_mode != IMAGE_MODE_LAYERED ||
+        Main_backups->Pages->Nb_layers!=5 || (Main_image_width%48))
     {
-      Verbose_message("Error!", "This emulation of Amstrad CPC's Mode5 needs all pixels of layer 5 to use colors 0-3.");
+      Verbose_message("Error!", "This emulation of Amstrad CPC's Mode5 can only be used on a 5-layer image whose width is a multiple of 48.");
       return;
     }
+    for (pixel=0; pixel < Main_image_width*Main_image_height; pixel++)
+    {
+      if (Main_backups->Pages->Image[4].Pixels[pixel]>3)
+      {
+        Verbose_message("Error!", "This emulation of Amstrad CPC's Mode5 needs all pixels of layer 5 to use colors 0-3.");
+        return;
+      }
+    }
+    // TODO set the palette to a CPC one ?
   }
-	// TODO backup
-	Switch_layer_mode(IMAGE_MODE_MODE5);
-	// TODO set the palette to a CPC one ?
+
+  // TODO backup
+  Switch_layer_mode(Selected_Constraint_Mode);
 }
 
 
 void Button_Constraint_menu(void)
 {
+  short clicked_button;
+  T_Dropdown_button* dropdown;
 
+  Open_window(154,79,"8-bit constraints");
+
+  Window_set_normal_button(21,55,51,14,"Cancel",0,1,KEY_ESC);  // 1
+  Window_set_normal_button(82,55,51,14,"OK"    ,0,1,SDLK_RETURN); // 2
+
+  dropdown = Window_set_dropdown_button(17, 21, 120, 14, 120, "Constraints", 1, 0, 1, RIGHT_SIDE|LEFT_SIDE, 0); // 3
+  //Window_dropdown_add_item(dropdown, IMAGE_MODE_ZX, "ZX Spectrum");
+  //Window_dropdown_add_item(dropdown, IMAGE_MODE_GBC, "Game Boy Color");
+  Window_dropdown_add_item(dropdown, IMAGE_MODE_EGX, "EGX (CPC)");
+  //Window_dropdown_add_item(dropdown, IMAGE_MODE_EGX2, "EGX2 (CPC)");
+  Window_dropdown_add_item(dropdown, IMAGE_MODE_MODE5, "Mode 5 (CPC)");
+
+  Update_window_area(0,0,Window_width, Window_height);
+  Display_cursor();
+
+  do
+  {
+    clicked_button=Window_clicked_button();
+
+    if (clicked_button == 3)
+      Selected_Constraint_Mode = Window_attribute2;
+  }
+  while ( (clicked_button!=1) && (clicked_button!=2) );
+
+  Close_window();
+
+  if (clicked_button==2) // OK
+  {
+    Button_Constraint_mode();
+  }
+
+  Display_cursor();
 }
 
 // Tilemap mode
diff --git a/src/const.h b/src/const.h
index 54eb5c7f..acab391f 100644
--- a/src/const.h
+++ b/src/const.h
@@ -4,7 +4,7 @@
 
     Copyright 2014 Sergii Pylypenko
     Copyright 2008 Yves Rizoud
-    Copyright 2007 Adrien Destugues
+    Copyright 2007-2017 Adrien Destugues
     Copyright 1996-2001 Sunset Design (Guillaume Dorme & Karl Maritaud)
 
     Grafx2 is free software; you can redistribute it and/or
@@ -589,6 +589,10 @@ enum IMAGE_MODES
 {
   IMAGE_MODE_LAYERED=0, ///< Layered image
   IMAGE_MODE_ANIMATION, ///< Animation
+  IMAGE_MODE_ZX,        ///< ZX Spectrum (note "SPECTRUM" is kept for later... Spectrum 512 anyone?)
+  IMAGE_MODE_GBC,       ///< Game Boy Color
+  IMAGE_MODE_EGX,       ///< CPC EGX
+  IMAGE_MODE_EGX2,      ///< CPC EGX2
   IMAGE_MODE_MODE5,     ///< CPC mode 5
 };
 
diff --git a/src/graph.c b/src/graph.c
index c6cd016c..0947a156 100644
--- a/src/graph.c
+++ b/src/graph.c
@@ -3003,6 +3003,28 @@ void Pixel_in_screen_layered_with_preview(word x,word y,byte color)
   }
 }
 
+void Pixel_in_screen_egx(word x,word y,byte color)
+{
+  if (y & 1)
+  {
+    Pixel_in_screen_layered(x & ~1,y,color);
+    Pixel_in_screen_layered(x |  1,y,color);
+  }
+  else
+    Pixel_in_screen_layered(x,y,color & 0xF3);
+}
+
+void Pixel_in_screen_egx_with_preview(word x,word y,byte color)
+{
+  if (y & 1)
+  {
+    Pixel_in_screen_layered_with_preview(x & ~1,y,color);
+    Pixel_in_screen_layered_with_preview(x |  1,y,color);
+  }
+  else
+    Pixel_in_screen_layered_with_preview(x,y,color & 0xF3);
+}
+
 /// Paint a a single pixel in image only : in a layer under one that acts as a layer-selector (mode 5).
 void Pixel_in_screen_underlay(word x,word y,byte color)
 {
@@ -3108,6 +3130,13 @@ void Update_pixel_renderer(void)
     Pixel_in_current_screen = Pixel_in_screen_layered;
     Pixel_in_current_screen_with_preview = Pixel_in_screen_layered_with_preview;
   }
+  else
+  if (Main_backups->Pages->Image_mode == IMAGE_MODE_EGX)
+  {
+    // layered
+    Pixel_in_current_screen = Pixel_in_screen_egx;
+    Pixel_in_current_screen_with_preview = Pixel_in_screen_egx_with_preview;
+  }
   // Implicit else : Image_mode must be IMAGE_MODE_MODE5
   else if ( Main_current_layer == 4)
   {
@@ -3123,7 +3152,7 @@ void Update_pixel_renderer(void)
   }
   else
   {
-    // layered (again)
+    // layered (again, for layers > 4 in MODE5)
     Pixel_in_current_screen = Pixel_in_screen_layered;
     Pixel_in_current_screen_with_preview = Pixel_in_screen_layered_with_preview;
   }
diff --git a/src/pages.c b/src/pages.c
index ba24f9ff..f9f46b73 100644
--- a/src/pages.c
+++ b/src/pages.c
@@ -3,7 +3,7 @@
 /*  Grafx2 - The Ultimate 256-color bitmap paint program
 
     Copyright 2008 Franck Charlet
-    Copyright 2007 Adrien Destugues
+    Copyright 2007-2017 Adrien Destugues
     Copyright 1996-2001 Sunset Design (Guillaume Dorme & Karl Maritaud)
 
     Grafx2 is free software; you can redistribute it and/or
@@ -1531,6 +1531,7 @@ void Switch_layer_mode(enum IMAGE_MODES new_mode)
   {
     case IMAGE_MODE_MODE5:
     case IMAGE_MODE_LAYERED:
+    default:
       Update_buffers(Main_image_width, Main_image_height);
       Redraw_layered_image();
       break;
diff --git a/src/palette.c b/src/palette.c
index 8fbfd8c4..53c36201 100644
--- a/src/palette.c
+++ b/src/palette.c
@@ -2,7 +2,7 @@
 */
 /*  Grafx2 - The Ultimate 256-color bitmap paint program
 
-    Copyright 2007 Adrien Destugues
+    Copyright 2007-2017 Adrien Destugues
     Copyright 1996-2001 Sunset Design (Guillaume Dorme & Karl Maritaud)
 
     Grafx2 is free software; you can redistribute it and/or
@@ -344,7 +344,8 @@ void Remap_image_highlevel(byte * conversion_table)
   int layer;
 
   // Remap the flatenned image view
-  if (Main_backups->Pages->Image_mode == IMAGE_MODE_LAYERED)
+  if (Main_backups->Pages->Image_mode != IMAGE_MODE_ANIMATION
+      && Main_backups->Pages->Image_mode != IMAGE_MODE_MODE5)
   {
     Remap_general_lowlevel(conversion_table,Main_visible_image.Image,Main_visible_image.Image,
                          Main_image_width,Main_image_height,Main_image_width);