Colours from uploaded Rhino models washed out

I am having trouble with models exported from Rhino (via OBJ). The models upload OK, but the colours are washed out compared to what they are in Rhino. For example a surface with material (plaster) RGB values of 127,187,142 turns up in Sketchfab with RGB values of 187,222,197 - i.e. significantly brighter and less saturated. I then have to edit each of the materials in Sketchfab to correct the colours. I have had a look at the RGB values in the .mtl files that go with each .obj file, and they match what is in Rhino (but obviously converted to decimal values - see below). Same thing happens if I export .dae files.
Definition of material from .mtl file:
newmtl Topo surface
Ka 0.0000 0.0000 0.0000
Kd 0.4980 0.7333 0.5569
Ks 1.0000 1.0000 1.0000
Tf 0.0000 0.0000 0.0000
d 1.0000
Ns 0.0000

What am I doing wrong?

What is the URL of this model?

I’ll have to upload it again bartv - I have already corrected the colours. It’s 10 pm here, but will do so in
the morning and supply two urls (one for the unchanged version and one matching the curs in Rhino.

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Good morning Bart. Two urls are below. I have uploaded a version that I have not manually corrected the colours in. Note that for the main topographic (green) surface:
The colours in Rhino are RGB are 127,187,142 (Hex code #7FBB8E) - this exports correctly to Kd 0.4980 0.7333 0.5569 in the .mtl file.

However, when uploaded to Sketchfab, the colour comes out as Hex code #BBDEC5 (RGB 187,222,197) - as I said in my original post, this is both lighter and less saturated than what it should be. Note that the same is true of the other materials in the model.
The uncorrected version can be found here
The version I have manually corrected each of the materials (so they are the same as in Rhino) can be found here.

Note that this has occurred with every model I have uploaded from Rhino. Any help or suggestions as to what I am doing wrong would be appreciated.

@james any insights? I wonder if Rhino uses color profiles?

Bart, for what it’s worth, I don’t think Rhino does. I did a test by making a hand-coded VRML file of a simple shape with the same colours as the Rhino object and then converted it to OBJ with a third party converter. The .mtl file created had the same colour vales as the one exported from Rhino, and suffered the same colour ‘conversion’ when uploaded to Sketchfab. Sketchfab seems to apply some algorithm to the colour values? Or it is something I am doing wrong!

Hi @Landy42,

Thanks for providing all these details. From what I read it seems to be a colorspace issue.
Usually, a washed out effect is visible when an original color is not interpreted using the good colorspace (~gamma value).
For a given color value, the linear version looks more saturated and constrasted than it’s sRGB counter part.

On Sketchfab, colors from RGB channels (Diffuse/Emissive/Specular) are interpreted as sRGB and we don’t do any specific operations on this. Also, I didn’t see any detail yet about how to interpet colors from OBJ files, so not sure if it’s actually on Rhino’s side or our side.

If by any chance there is a settings for colorspace in Rhino (in the project or in the export box) mentionning Linear or sRGB, it would worth an export with the setting set in sRGB.

We will investigate and see if we can improve or fix this

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Thank you for your response Waleguene. I don’t think it is at the Rhino end. There does not seem to be any options in the export dialog box in Rhino, but I am unsure what colour space Rhino operates in (will investigate). As I said in my last response, the same thing happens with hand-coded vrml. I have tried editing the mtl files, but it seems to make little difference. I think you are correct that the conversion to sRGB is the issue. It would be good to have an option in the 3D settings editor on Sketchfab to alter how the colours are translated. I will also pose this question on the Rhino forums - I have not done so to date as there is an issue with my Rhino login at the moment.

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