Rhino 6: Decal changes material colour

Hi, I noticed this, but not sure why.

Adding a decal changes the colour of the surface in Raytraced view. As seen in Fig1, the surface with decal is turns darker than the usual (the small rectangle, split from the surface is the original). This could be replicated with an empty .png file.

Fig2 shows the effect when decal is removed. Fig3 is just for information.

Material has not been changed throughout (plastic in this case). Using SR14.

With empty PNG do you mean one that is fully transparent?

edit ps: moved to Rendering category.

Yes, one that is fully transparent.

@thecheongjh I am unable to replicate the behaviour. Applying a decal that has alpha channel does not darken the material:

decal_with_alpha_basematerial_tester.3dm (304.8 KB)

I see it happens with i.e. plastic material.

The problem here is that currently the decal gets baked into a texture that is mapped to the entire object. Unfortunately that combined with how decals are to be interpreted in v6 slightly changes the action on the surface when the BSDFs are calculated. This will be fixed in v7 when Raytraced doesn’t bake decals anymore.

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