diff --git a/CHANGELOG.md b/CHANGELOG.md
index 991f792..7f03a9e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,11 @@ Activate / deactivate layer opacity according to prefix
 Activate / deactivate all masks using MA layers
 -->
 
+1.3.0
+
+- added: Preview with a combined alpha over of all render layer available
+- added: button to clear preview nodes
+
 1.2.3
 
 - added: autobuild set each gp objects data to single user
diff --git a/OP_merge_layers.py b/OP_merge_layers.py
index d59193c..7ed4d3e 100644
--- a/OP_merge_layers.py
+++ b/OP_merge_layers.py
@@ -1,6 +1,7 @@
 import bpy
 import re
 from math import isclose
+from itertools import groupby
 from . import fn
 from . import gen_vlayer
 
@@ -114,6 +115,126 @@ def merge_layers(rlayers, obname=None, active=None, disconnect=True, color=None)
 
     return ng, out
 
+def merge_compositor_preview(context=None, clear=False):
+    '''Merge all active render layer with alpha over.location[0]+450, ng.location[1]+50), width=600)
+    Create a dedicated node group and connect to compositor output
+    return tuple(merge nodegroup, compositor out)
+    '''
+
+    context = context or bpy.context
+    node_tree = context.scene.node_tree
+    nodes = node_tree.nodes
+    links = node_tree.links
+
+    ## identify all duplicated render layer and remove them, then recreate the preview
+    for n in reversed(nodes):
+        if n.type in ('R_LAYERS', 'GROUP') and n.get('is_preview'):
+            nodes.remove(n)
+    
+    ng_name = f'merge_NG_preview'
+    ## clear unused nodes groups duplication
+    fn.clear_nodegroup(ng_name, full_clear=True)
+
+    if clear:
+        ## Restore to jpg out ?
+        # im_settings = context.scene.render.image_settings
+        # im_settings.file_format = 'JPEG'
+        # im_settings.color_mode = 'RGB'
+        # im_settings.quality = 0
+        return
+
+    ## Get all RL node per object block (node frames), sort object by name (should a)
+    
+    all_rlayers = [n for n in nodes if n.type == 'R_LAYERS']
+    all_rlayers.sort(key=lambda x: x.label, reverse=True)
+
+    ## ! All at once doe not work, need to separate by individual object first
+    # all_rlayers.sort(key=lambda x: (x.label, -fn.real_loc(x).y))
+
+    ## Sort all render layer by object (either by start name or by frames)
+    ## sort order within by order in layer stack (check -n.location.y or associated gp object)
+    
+    grps = groupby(all_rlayers, key=lambda x : x.label.split(' /')[0])
+    
+    rlayers_groups = {k : sorted(list(grp), key=lambda x: x.location.y, reverse=True) for k, grp in grps if k}
+
+    # Debug prints
+    # for ob_key_name, rl_group in rlayers_groups.items():
+    #     print(ob_key_name)
+    #     for n in rl_group:
+    #         print(f'- {n.label}')
+    #     print()
+    # print('Done')
+
+    ## Recreate the render layer nodes duplicated at the side of the frames
+    
+    pos_x = 2400
+    pos_y = 30
+    offset_y = 180
+    comp_list = []
+    for k, rl_group in rlayers_groups.items():
+        for rl in rl_group:
+            comp = nodes.new('CompositorNodeRLayers')
+            comp['is_preview'] = 1
+            comp.label = rl.label # f'.{rl.label}'
+            comp.name = f'.{rl.name}'
+            comp.scene = rl.scene
+            comp.layer = rl.layer
+            comp.color = rl.color
+            comp.use_custom_color = True
+            comp.width = rl.width
+            comp.show_preview = False
+            comp.location = (pos_x, pos_y)
+            comp_list.append(comp)
+            pos_y -= offset_y
+
+
+    ### Create the nodegroup for clean alpha over merge
+
+    ## Need a unique nodegroup name, increment name while nodegroup exists
+    # while bpy.data.node_groups.get(ng_name): # nodes.get(ng_name)
+    #     if not re.search(r'(\d+)$', ng_name):
+    #         ng_name += '_02' # if not ending with a number add _02
+    #     ng_name = re.sub(r'(\d+)(?!.*\d)', lambda x: str(int(x.group(1))+1).zfill(len(x.group(1))), ng_name)
+
+    print(f'Create preview merge nodegroup {ng_name}')
+
+    ngroup = bpy.data.node_groups.new(ng_name, 'CompositorNodeTree')
+    ng = fn.create_node('CompositorNodeGroup', tree=node_tree, location=(3000, 0), width=400)
+    ng.node_tree = ngroup
+    ng.name = ngroup.name
+    ng['is_preview'] = 1
+    fn.create_node('NodeGroupInput', tree=ngroup, location=(-600,0))
+    fn.create_node('NodeGroupOutput', tree=ngroup, location=(1000,0))
+
+    # Create inputs and links to node_group
+    for rln in comp_list:
+        rln.outputs['Image']
+        sockin = ng.inputs.new('NodeSocketColor', rln.layer)
+        sockin = ng.inputs[-1]
+        links.new(rln.outputs['Image'], sockin)
+
+    fn.nodegroup_merge_inputs(ng.node_tree)
+    ng.update()
+    
+    # Create composite out (if needed) and connect
+    composite_out = next((n for n in nodes if n.type == 'COMPOSITE'), None)
+    if not composite_out:
+        composite_out = fn.create_node('CompositorNodeComposite', tree=node_tree, location=(ng.location[0]+450, ng.location[1]+50), width=140)
+    composite_out.use_alpha = True
+    links.new(ng.outputs[0], composite_out.inputs[0])
+    
+    im_settings = context.scene.render.image_settings
+    # im_settings.file_format = 'JPEG'
+    # im_settings.color_mode = 'RGB'
+    # im_settings.quality = 0
+    im_settings.file_format = 'OPEN_EXR'
+    im_settings.color_mode = 'RGBA'
+    im_settings.color_depth = '16'
+    im_settings.exr_codec = 'ZIP'
+
+    return ng, composite_out
+
 class GPEXP_OT_merge_viewlayers_to_active(bpy.types.Operator):
     bl_idname = "gp.merge_viewlayers_to_active"
     bl_label = "Merge selected layers view_layers"
@@ -145,6 +266,21 @@ class GPEXP_OT_merge_viewlayers_to_active(bpy.types.Operator):
             self.report(*ret)
         return {"FINISHED"}
 
+class GPEXP_OT_merge_preview_ouput(bpy.types.Operator):
+    bl_idname = "gp.merge_preview_ouput"
+    bl_label = "Merge Preview Output"
+    bl_description = "Merge all active render layers to an output"
+    bl_options = {"REGISTER"}
+
+    # @classmethod
+    # def poll(cls, context):
+    #     return True
+
+    clear : bpy.props.BoolProperty(default=False, options={'SKIP_SAVE'})
+
+    def execute(self, context):
+        merge_compositor_preview(context=context, clear=self.clear)
+        return {"FINISHED"}
 
 class GPEXP_OT_auto_merge_adjacent_prefix(bpy.types.Operator):
     bl_idname = "gpexp.auto_merge_adjacent_prefix"
@@ -285,6 +421,7 @@ GPEXP_OT_merge_viewlayers_to_active,
 GPEXP_OT_auto_merge_adjacent_prefix,
 GPEXP_OT_merge_selected_dopesheet_layers,# unused
 GPEXP_OT_merge_selected_viewlayer_nodes,
+GPEXP_OT_merge_preview_ouput,
 )
 
 def register():
diff --git a/__init__.py b/__init__.py
index aecbdf0..f21e445 100644
--- a/__init__.py
+++ b/__init__.py
@@ -2,7 +2,7 @@ bl_info = {
     "name": "GP Render",
     "description": "Organise export of gp layers through compositor output",
     "author": "Samuel Bernou",
-    "version": (1, 2, 3),
+    "version": (1, 3, 0),
     "blender": (2, 93, 0),
     "location": "View3D",
     "warning": "",
diff --git a/fn.py b/fn.py
index d051750..85514d5 100644
--- a/fn.py
+++ b/fn.py
@@ -182,9 +182,16 @@ def set_settings(scene=None, aa=True):
 
     # output (fast write settings since this is just to delete afterwards...)
     scene.render.filepath = f'//render/preview/{scene.name}/preview_'
-    scene.render.image_settings.file_format = 'JPEG'
-    scene.render.image_settings.color_mode = 'RGB'
-    scene.render.image_settings.quality = 0
+    im_settings = scene.render.image_settings
+    # im_settings.file_format = 'JPEG'
+    # im_settings.color_mode = 'RGB'
+    # im_settings.quality = 0
+
+    ## Same as output nodes
+    im_settings.file_format = 'OPEN_EXR'
+    im_settings.color_mode = 'RGBA'
+    im_settings.color_depth = '16'
+    im_settings.exr_codec = 'ZIP'
 
 def scene_aa(scene=None, toggle=True):
     '''Change scene AA settings and commute AA nodes according to toggle'''
@@ -1702,4 +1709,4 @@ def clean_mats_duplication(ob, skip_different_materials=True):
 
     if diff_ct:
         print(f'{diff_ct} mat skipped >> same name but different color settings!')
-        # return ('INFO', f'{diff_ct} mat skipped >> same name but different color settings!')
\ No newline at end of file
+        # return ('INFO', f'{diff_ct} mat skipped >> same name but different color settings!')
diff --git a/ui.py b/ui.py
index c7945f2..10ec309 100644
--- a/ui.py
+++ b/ui.py
@@ -117,6 +117,10 @@ class GPEXP_PT_gp_node_ui(Panel):
         subcol = col.column()
         subcol.enabled = bool(ct)
         subcol.operator('gp.number_outputs', icon='LINENUMBERS_ON', text=txt).mode = 'SELECTED'
+        
+        row=layout.row(align=True)
+        row.operator('gp.merge_preview_ouput', icon='NODETREE', text='Set Preview')
+        row.operator('gp.merge_preview_ouput', icon='X', text='').clear = True
         # subcol.operator('gp.normalize_outnames', icon='SYNTAX_OFF', text=f'Normalize Paths {ct} Selected Ouptut') # not ready
         # col.operator('gp.number_outputs', icon='LINENUMBERS_ON', text='Renumber all outputs').mode = 'ALL'