Clean up the mesh:
In edit mode:
Top view
Circle wanted object (C key, then roll mouse wheel) → R click (get out of selection)
Inverse (Ctrl I)
Delete surrounding wanted object (delete face)
Export as obj
Open Instant Mehes (to reduce ploygon as a lower resolution mesh)
Reduce Target Vertex count to about 10k
Put the object run form top to bottom and left to right
Use the 1st comb tool, draw lines in the middle of the each part of mesh (after drwaing, will show the cross)
Click on Solve
Click Export mesh, set as follow (click Extrach mesh to check how the output look, set iteration to 0 if too little ploygon left to export)
Click save
Reimport low rev mesh in blender:
Open the original blender project (with original mesh on), import the obj mesh newly created
(should overlapping both the old (high rev) and new (low rev) meshes together
Rename the high and low rev layers
Open low rev mesh in Edit mode, select Edge mode, see if any blue lines on mesh
If yes, select all → R click → Clear Sharp
R click on low rev mesh in Object mode → Shade Smooth
Repair holes:
In edit mode of the low rev mesh, select those holes area (to make them all hollow)
(C key, L click select, middle click diselect, R click go out select C key mode)
Delete Faces
To fix small holes, use Edge selection, select the surrounding, hit F key
Then use knife tool to create the geometry lines
Unwrap the low rev mesh to create a UV map
Haven’t continue as it takes long time, but basically the remained steps are:
Add shader (image texture node for diffuse and normal map) (in Shader Editor node graph)
Bake the high rev mesh onto the low rev mesh (by baking the diffuse map and normal map)
In Sculpting menu to repair the holes after connect baked texture to low rev mesh (high rev mesh is no longer needed)
in Texture Paint menu , Use Clone and stamp tool to fix the texture color on the holes:
Smoothen outer boundary (only if the object outside has such problem)