LRV and Vray

[carlos_caballero]

Hi all,

I've tried to search Light Reflective Value here on the forums without success. My question is how can I apply the LRV values such as what paint manufacturers use (Horizon OC-53 | Benjamin Moore) into my materials to better simulate the reflective properties of the real paint?

I would appreciate any pointers or info anyone is willing to share.

Thanks!

[DougBowker]

Just bumping this thread up as I have the same question.

[^Lele^]

Assuming it's measured orthogonally, this would be albedo.
For an opaque, reflective paint, it would be the sum of the diffuse plus reflection colors' value, expressed as a float.
Rendering with furnace lighting (a pure white domelight), you can color pick the paint in the VFB in a perfectly camera-facing area, and your LRV will be this value to the right, multiplied by 100 to rerange it to the LRV:


Done under any lighting, sum the diffuse filter and reflection filter render elements, and pick the value.

[dlparisi]

Thanks Lele. I know it's not your area of expertise but do you have any idea how the LRV relates to the RGB values of paint colors? I usually just use the RGB values plugged into a VrayColor map set to a gamma of 2.2 and they render out fine but these values don't seem to align with the published LRV values.

[^Lele^]

Eh, off the top of my head, it's hard to figure out.
Feel free to poke me privately and send me the relevant material, so we may try it out.

[dlparisi]

Sorry, I should have been more clear, the LRV values are correct (I guess as I can't really measure them) but the LRV values don't really match the HSV values picked in the frame buffer. After some further googling I think the LRV is just a different measurement than the 'V" in HSV. I used three paint colors in the image below: PPG Elemental, Benjamin Moore Spring Tulip, and PPG Corn Silk. The website EasyRGB has slightly different values for some of the RGB values but they're close enough. You could argue that the Elemental one is close with the LRV at 66 and the clicked value at .7 for the raw but the others are way off, especially the Spring Tulips (22.26 vs .8!). From what I could find online it seems that the LRV value, when computed rather than measured, is based off the CIELAB L* component from what I found here. That is the only place I found that conversion though, but the math does work out to get a number that is very close to the published LRVs (within 1 or 2 digits). It seems like the CIELAB L* lightness value is based on perceived lightness so perhaps this accounts for the discrepancy? In short, I don't think the LRV is useful in any way for our work as we can't use it in any map or measure it directly in the frame buffer. I'm going to safely ignore any LRV value I see and just focus on the RGB values. Perhaps I'm misunderstanding something though. Scene attached as well.


RGB-LRV Test.zip