Reflection colour and IOR

[Guest]

This is always something that I have never fully grasped. The reflection colour determines the strength of the reflection but how do we know what RGB value to put in there? From experience I use certain RGB values but I never know of its actually correct. In combination with fresnel it gets even more complicated and into the unknown. I know there are fresnel IOR values out there for certain materials so I tend to stick with these. There is also a difference between gamma 1 and gamma 2.2. Reflections appear much stronger if the same RGB value is used, so I usually reduce this, but again never sure how much to reduce it by or if it was correct in the first place.

I tend to stick in the IOR value I know and start at RGB 128, 128, 128 as a mid point for the reflection and either increase or decrease it depending on the results.

Typically for a super high glossy plastic type material I set the fresnel to 2 and set the RGB reflection to 120,120,120. It looks OK, but I never know if its actually correct. Just wondered how others go about this issue? Is it all just guess work or is there a table somewhere that has rough guides on RGB values against fresnel? I know that each plastic material would be different but I would have thought that there was sort of common starting point for the most common materials.

Thanks,

[joconnell]

If it's a pure material and totally clean, put in pure white and let the fresnel curve do the rest. Most pure materials tend to go to 100% reflective at the very edge (90 degrees) and the fresnel curve will take care of the rest of the values. This is only for perfect / pure materials though which few are, so if you know what a material is, do as you are and put in the correct ior to start with and then play with the whiteness of your reflection colour. If you had a sample of the material you're trying to recreate, you could probably put a flat coloured object beside it, photograph it and compare the original vs the reflected version to get a sense of what percent the reflection is at.

The problem is the material and the lighting affect each other so much, you really have to have one locked down as "correct" to confidently tweak the other.

[Guest]

Thanks for your response