How to display and use Vertex Color from OBJ model

Question

Recently, I found this funny site, that allows you to generate a 3D model from a 2D image.

It works very well and you can download an OBJ file. Vertex are colored and when I import it using Blender, I can't see any Vertex color.

Using Cycle (I prefer a internal solution if it exists) according to some answers I've found on Blender Stack Exchange, I patched some nodes : Attribute -> Diffuse BDSF -> Material Output.

Unfortunately, I can't get it works, the model stills black.

When I open the OBJ file, I see that color per vertex are there :

v 43.747554 107.000000 69.000000 0.470588 0.380392 0.309804
v 43.780163 115.000000 64.500000 0.427451 0.337255 0.266667
v 43.782527 107.000000 68.500000 0.470588 0.380392 0.309804
v 43.801902 115.000000 65.000000 0.427451 0.337255 0.266667
v 43.806461 107.000000 69.500000 0.470588 0.380392 0.309804
v 43.821703 115.000000 64.000000 0.427451 0.337255 0.266667
v 43.838352 108.000000 68.500000 0.466667 0.376471 0.305882
v 43.854670 106.000000 69.000000 0.482353 0.392157 0.321569
v 43.856176 108.000000 69.000000 0.466667 0.376471 0.305882
v 43.873876 106.000000 69.500000 0.482353 0.392157 0.321569
v 43.888855 110.000000 68.000000 0.466667 0.376471 0.305882
v 43.891471 109.000000 68.000000 0.466667 0.376471 0.305882
v 43.892733 110.000000 67.500000 0.466667 0.376471 0.305882
v 43.895170 108.000000 68.000000 0.466667 0.376471 0.305882
v 43.900904 109.000000 68.500000 0.466667 0.376471 0.305882
v 43.907584 107.000000 68.000000 0.470588 0.380392 0.309804
v 43.917898 115.000000 65.500000 0.427451 0.337255 0.266667
v 43.925000 111.000000 67.500000 0.454902 0.364706 0.294118

According to some answers here, Blender import more easily the vertex color of a PLY file so I tried to convert to PLY with two different sites :

1. meshconvert .com : Give me a 3.5 Mo file

2. greentoken.de/onlineconv : Give me a 2.3 Mo file

(Of course, if you know some other sites I could try, it interest me)

I guess that color data are lost with greentoken (not sure).

When I import the 3.5 Mo PLY file in blender, I need to be in textured display mode, then I think I see my vertex color value but in black & white instead of RGB, that is weird. Anyway, I can't get it work

EDIT 1 : I opened PLY files and color vertex aren't there... I need to find a better converter

EDIT 2 : I tried www.ofoct.com/3d-model-file-for-3d-printer-converter it doens't take vertex color into account. In fact, in each PLY files I converted with the various sites here, there is a common line :

comment Created by Open Asset Import Library - http://assimp.sf.net (v3.2.0)

(the version varies)

EDIT 3 : In fact it seems that model converted by Green token, keep the vertex color. That is weird because that's the smallest file :

ply
format ascii 1.0
comment Created by Open Asset Import Library - http://assimp.sf.net (v3.1.187496374)
element vertex 29793
property float x
property float y
property float z
property float nx
property float ny
property float nz
element face 59582
property list uint uint vertex_index
end_header
82 103 6.37528 0.40963 0.0331735 0.911648
82 102 6.57043 0.272087 0.235193 0.933088
82.6603 103 6.5 -0.14071 0.043367 0.9891
82 103.935 6.5 0.201161 -0.136681 0.969976
81.5475 103 7 0.825371 0.0489484 0.562465
83 102 6.62244 -0.248588 0.147929 0.957247
83 103 6.56417 -0.411487 -0.0867124 0.907281
81.5819 104 7 0.787841 -0.0338904 0.614946
82 105 6.63886 0.0715144 -0.131383 0.988749
83 104 6.77321 -0.431167 -0.171652 0.885794
83.6781 102 7 -0.470137 0.061235 0.880467
83.6327 103 7 -0.543939 -0.0905203 0.834228
83 105 6.96709 -0.445324 -0.163091 0.880391
84 103 7.23724 -0.520118 -0.141377 0.842313
84 104 7.47775 -0.546517 -0.195833 0.814229
84 102 7.16782 -0.416323 -0.021798 0.908955
83.3508 101 7 -0.314426 0.156435 0.936304
84 101 7.22581 -0.280388 0.0301462 0.959413
84.9009 101 7.5 -0.339848 -0.0219793 0.940223
84.6939 102 7.5 -0.435242 -0.0925323 0.895546

As you can see, nx, ny and nz correspond to RGB values..

Answer 1

As others stated, the OBJ format specification officially does not have the ability to contain any vertex color information, but some apps extend the format to support this feature (RGB values are appended after vertex position values).

I managed to modify the Blender's OBJ importer to import & assign vertex colors as well.

Caution - the current implementation is really dirty at this moment (I am going to dig into the code more in the future), also I have not tested it properly so some bugs can occur.

DOWNLOAD / HOW TO USE

To try the modified importer, download the latest version of the import_obj.py script from my GitHub repo and replace the original one located in blender\2.x\scripts\addons\io_scene_obj (make a backup of the previous one, of course).

Then just cross all your fingers and try importing an OBJ model. To see vertex colors clearly, create & assign a new material to the object, set it Shadeless and enable Vertex Color Paint in Options. Then just set the 3D view shading to Material (as in the gif below).

This is an example of an OBJ model exported from http://www.cs.nott.ac.uk/~psxasj/3dme/index.php and imported using the modified importer:

Please let me know whether it works for you!

Answer 2

Thanks to Carlo's comment. Meshlab did it ! I just had to import the OBJ mesh and export it as PLY. Then, I import the mesh in Blender, add a material and just check Vertex Color Paint in option for blender internal rendering. Works like a charm :)

EDIT 2021 (Blender 2.92)

I also had to convert the mesh using Meshlab into a PLY format. Then with Eevee or Cycle, I had to use the node Vertex Color like this: