diff --git a/src/brush.c b/src/brush.c
index 29cc7f4c..ca7fff7a 100644
--- a/src/brush.c
+++ b/src/brush.c
@@ -124,7 +124,7 @@ void Display_paintbrush(short x,short y,byte color)
   if (Mouse_K) // pas de curseur si on est en preview et 
     return;                  // en train de cliquer
     
-  if (Constraint_mode && Main_current_layer < 4)
+  if (Main_backups->Pages->Image_mode == IMAGE_MODE_MODE5 && Main_current_layer < 4)
   {
     goto single_pixel;
   }
@@ -292,7 +292,7 @@ void Draw_paintbrush(short x,short y,byte color)
   int position;
   byte old_color;
 
-  if (Constraint_mode && Main_current_layer < 4)
+  if (Main_backups->Pages->Image_mode == IMAGE_MODE_MODE5 && Main_current_layer < 4)
   {
     // Flood-fill the enclosing area
     if (x<Main_image_width && y<Main_image_height && x>= 0 && y >= 0
diff --git a/src/buttons.c b/src/buttons.c
index 65181850..dee3eb25 100644
--- a/src/buttons.c
+++ b/src/buttons.c
@@ -4514,7 +4514,7 @@ void Display_effect_states(void)
   Display_effect_state(C2+23, 81, "Grid"   ,Snap_mode);
   Display_effect_state(C2+23,100, "Tiling" ,Tiling_mode);
 
-  Display_effect_state(177+23,24, "8 bit"  ,Constraint_mode);
+  Display_effect_state(177+23,24, "8 bit"  ,Main_backups->Pages->Image_mode > IMAGE_MODE_ANIMATION);
   Display_effect_state(177+23,43, "Tilemap",Main_tilemap_mode);
 }
 
@@ -4800,7 +4800,7 @@ void Button_Effects(void)
         {
           Button_Constraint_mode();
           Hide_cursor();
-          Display_effect_state(177+23,24, "8 bit" ,Constraint_mode);
+          Display_effect_state(177+23,24, "8 bit" ,Main_backups->Pages->Image_mode > IMAGE_MODE_ANIMATION);
           Display_cursor();
         } else {
           Close_window();
@@ -4834,7 +4834,7 @@ void Button_Effects(void)
   else
     Hide_cursor();
 
-  if (!(Shade_mode||Quick_shade_mode||Colorize_mode||Smooth_mode||Tiling_mode||Smear_mode||Stencil_mode||Mask_mode||Sieve_mode||Snap_mode||Constraint_mode||Main_tilemap_mode))
+  if (!(Shade_mode||Quick_shade_mode||Colorize_mode||Smooth_mode||Tiling_mode||Smear_mode||Stencil_mode||Mask_mode||Sieve_mode||Snap_mode||Main_tilemap_mode))
     Unselect_button(BUTTON_EFFECTS);
 
   Display_cursor();
diff --git a/src/buttons_effects.c b/src/buttons_effects.c
index 3a74f984..3186253c 100644
--- a/src/buttons_effects.c
+++ b/src/buttons_effects.c
@@ -167,10 +167,9 @@ void Menu_tag_colors(char * window_title, byte * table, byte * mode, byte can_ca
 // Constaint enforcer/checker ------------------------------------------------
 void Button_Constraint_mode(void)
 {
-  Constraint_mode=!Constraint_mode;
-  
-  if (Constraint_mode)
+  if (Main_backups->Pages->Image_mode == IMAGE_MODE_LAYERED)
   {
+    Main_backups->Pages->Image_mode = IMAGE_MODE_MODE5;
   	// TODO backup
   	// CPC Mode 5 - ensure there are at least 5 layers
   	while(Main_backups->Pages->Nb_layers < 5)
@@ -182,6 +181,11 @@ void Button_Constraint_mode(void)
   	
   	// TODO set the palette to a CPC one ?
   }
+  else if (Main_backups->Pages->Image_mode == IMAGE_MODE_MODE5)
+  {
+    // Disable
+    Main_backups->Pages->Image_mode = IMAGE_MODE_LAYERED;
+  }
 }
 
 
@@ -906,7 +910,6 @@ void Effects_off(void)
   Mask_mode=0;
   Sieve_mode=0;
   Snap_mode=0;
-  Constraint_mode=0;
   Main_tilemap_mode=0;
 }
 
diff --git a/src/const.h b/src/const.h
index adb9a730..9a68caf1 100644
--- a/src/const.h
+++ b/src/const.h
@@ -564,4 +564,11 @@ enum OPERATIONS
   NB_OPERATIONS                ///< Number of operations handled by the engine
 };
 
+enum IMAGE_MODES
+{
+  IMAGE_MODE_LAYERED=0, ///< Layered image
+  IMAGE_MODE_ANIMATION, ///< Animation
+  IMAGE_MODE_MODE5,     ///< CPC mode 5
+};
+
 #endif
diff --git a/src/global.h b/src/global.h
index 86b9952f..54583d67 100644
--- a/src/global.h
+++ b/src/global.h
@@ -726,11 +726,6 @@ GFX2_GLOBAL byte Mask_mode;
 /// Array of booleans. True if the indexed color is protected by the mask.
 GFX2_GLOBAL byte Mask_table[256];
 
-// -- Constraint mode
-
-/// Constraint enforcer
-GFX2_GLOBAL byte Constraint_mode;
-
 // -- Tilemap mode
 
 /// Tilemap mode for main page
diff --git a/src/graph.c b/src/graph.c
index e62451dc..119cf8a2 100644
--- a/src/graph.c
+++ b/src/graph.c
@@ -3009,7 +3009,7 @@ byte Read_pixel_from_current_screen  (word x,word y)
   byte depth;
   byte color;
 
-  if (Constraint_mode)  
+  if (Main_backups->Pages->Image_mode == IMAGE_MODE_MODE5)  
     if (Main_current_layer==4)
       return *(Main_backups->Pages->Image[Main_current_layer].Pixels + x+y*Main_image_width);
     
@@ -3163,12 +3163,13 @@ byte Read_pixel_from_current_layer(word x,word y)
 void Update_pixel_renderer(void)
 {
   #ifndef NOLAYERS
-  if (!Constraint_mode)
+  if (Main_backups->Pages->Image_mode == IMAGE_MODE_LAYERED)
   {
     // layered
     Pixel_in_current_screen = Pixel_in_screen_layered;
     Pixel_in_current_screen_with_preview = Pixel_in_screen_layered_with_preview;
   }
+  // Implicit else : Image_mode must be IMAGE_MODE_MODE5
   else if ( Main_current_layer == 4)
   {
     // overlay
diff --git a/src/miscfileformats.c b/src/miscfileformats.c
index bc82be6b..8c4a6c2f 100644
--- a/src/miscfileformats.c
+++ b/src/miscfileformats.c
@@ -3021,8 +3021,8 @@ void Load_CM5(T_IO_Context* context)
   // Now select layer 0 again
   Set_loading_layer(context, 0);
 
-  if (Constraint_mode != 1)
-    Constraint_mode = 1;
+  if (context->Type == CONTEXT_MAIN_IMAGE)
+    Main_backups->Pages->Image_mode = IMAGE_MODE_MODE5;
 
   for(ty=0; ty<context->Height; ty++)
   for(tx=0; tx<context->Width; tx++)
diff --git a/src/pages.c b/src/pages.c
index 73ba7bf3..e51f5881 100644
--- a/src/pages.c
+++ b/src/pages.c
@@ -73,6 +73,7 @@ T_Page * New_page(int nb_layers)
     }
     page->Width=0;
     page->Height=0;
+    page->Image_mode = IMAGE_MODE_LAYERED;
     memset(page->Palette,0,sizeof(T_Palette));
     page->Comment[0]='\0';
     page->File_directory[0]='\0';
@@ -203,7 +204,7 @@ void Redraw_layered_image(void)
   // Re-construct the image with the visible layers
   byte layer=0;  
   // First layer
-  if (Constraint_mode && Main_layers_visible & (1<<4))
+  if (Main_backups->Pages->Image_mode == IMAGE_MODE_MODE5 && Main_layers_visible & (1<<4))
   {
     // The raster result layer is visible: start there
     // Copy it in Main_visible_image
@@ -484,7 +485,7 @@ int Allocate_list_of_pages(T_List_of_pages * list)
   T_Page * page;
 
   // On initialise chacune des nouvelles pages
-  page=New_page(NB_LAYERS);
+  page=New_page(1);
   if (!page)
     return 0;
   
@@ -911,6 +912,7 @@ int Backup_with_new_dimensions(int width,int height)
   Main_backups->Pages->Gradients=Dup_gradient(Main_backups->Pages->Next);
   Main_backups->Pages->Background_transparent=Main_backups->Pages->Next->Background_transparent;
   Main_backups->Pages->Transparent_color=Main_backups->Pages->Next->Transparent_color;
+  Main_backups->Pages->Image_mode=Main_backups->Pages->Next->Image_mode;
   
   // Fill with transparent color
   for (i=0; i<Main_backups->Pages->Nb_layers;i++)
diff --git a/src/struct.h b/src/struct.h
index 627b9c60..1271c187 100644
--- a/src/struct.h
+++ b/src/struct.h
@@ -401,6 +401,8 @@ typedef struct T_Page
   int       Height;  ///< Image height in pixels.
   T_Palette Palette; ///< Image palette.
 
+  byte      Image_mode; ///< 0= layered image, 1=animation,
+
   char      Comment[COMMENT_SIZE+1]; ///< Comment to store in the image file.
 
   char      File_directory[MAX_PATH_CHARACTERS];///< Directory that contains the file.