Rgb reference values for various materials

[stevesideas]

Hi there,

Im currently doing an arch vis scene. I often find I have problems with knowing how bright a particular texture should be for the setup I have created.

I normally start off with a vraysun/sky. Then i set the iso to 200, F-stop to 16 and then the shutter speed to something like 250. I then set a basic white material with RGB value of 157. Is this white values correct for that kind of setup ?

Then I would like to know what RGB values would be for materials such as grass, concrete wall etc so that I can stop rendering so many test scenes and have a more flowing type of process.

Is there a list out there that says, white in Vray with a vraycamera should be set to RGB 157, grass RGB should be near values.....

Any advice appreciated.

[stevesideas]

Actually, I just found this...would you say this was accurate ?

http://software.asgvis.com/index.php...v-ray-for-rino

[glorybound]

Color Theory

I think a book on color theory would help you, it helped me.

I usually set up my scenes with lights and a camera, place a box with a white material, and expose the camera until my float is around 1,1,1. I turn off clamping and I am in linear space for this.

[DanielBrew]

Steve,

I normally start off with a vraysun/sky. Then i set the iso to 200, F-stop to 16 and then the shutter speed to something like 250. I then set a basic white material with RGB value of 157. Is this white values correct for that kind of setup ?

I think you on the right lines with this. If you follow your logic through then you should set the 'RGB Level' for bitamps to about 0.61 (157/255). You should also limit the RGB values of other materials like procedurals etc. to below 157 as well.

I did a bit of reading about this a while ago. I remember reading that fresh snow is one of the most reflective diffuse materials and that reflects about 80% of light. So you're probably not far of with a value of 61% for white paint. I settled on a value of RGB 200 for white paint. I know it's not physically accurate but it makes lighting interiors easier with fewer dark corners. I suppose it depends on what your final output is for. Most clients want interior renders to be brighter that your average interior photogragh.

Hope this helps

Dan

[stevesideas]

Thanks for the advice. At least I know my process isnt too far off. I may up my white values for future scenes as Ive read a number of people using around 200rgb for white....see how that works out.

Yeah, I think a book would probably help too. Im still reading vray, the complete guide....

[stevesideas]

I think a book on color theory would help you, it helped me.

I usually set up my scenes with lights and a camera, place a box with a white material, and expose the camera until my float is around 1,1,1. I turn off clamping and I am in linear space for this.

But doesnt the float vary quite a bit between the faces that are lit directly by the sun and those that are only lit by gi or are in shadow ?

[chrisjacks21]

Interesting topic Steve. I have always made sure my white materials were not 100% white, but didnt realise the theory was to go as low as rgb200 or even rgb157!

[werticus]

rgb 125 is white for me

[lllab]

to my knowledge rgb 220 (some say around 230) is more or less the correct "white" value. / this is the physical measured white of a white sheat of paper. used very often time in realworld to get the white point.

i recommend also reading info about photography. 99% is also true for vray rendering.

cheers
stefan

[stevesideas]

Its obvious that no-one seems to use the same white value and still get satisfactory results. I think I will go with the knowledge that 80% of light is reflected from a white surface and so I guess RGB 176 will be my new white value from now on.

I wonder if that is based on a white high gloss surface or a matt white surface

[DanielBrew]

to my knowledge rgb 220 (some say around 230) is more or less the correct "white" value.

This has been discussed before, see Vlado's comments in this thread.
http://www.chaosgroup.com/forums/vbu...t=Reflectivity

I wonder if that is based on a white high gloss surface or a matt white surface

Reflectivity (or albedo) values are normally done using a totally matt surface, I think they grind the material to a very fine powder before measuring. I think you can get much higher values from a gloss surface.

[stevesideas]

I guess I will base it on a matt surface and then if anything is reflective it should be physically correct...

[pixela]

I usualy put a grey128 material on all objects and make lighting. I try to get the medium grey in render out put too. Then I put 225grey for white and increase lighting only a bit. And then try to put proportional values for all materials in between.

I am sometimes confused about physical accuracy. The reflactance value is also how much light is bounced in real life- am I wrong?
So then do we need to put reflective materials (maybe even fake reflective values) so that light bounces off more and get brighter renders?

I can never decide which approach is better. And honestly I really feel mixed up. So I always give up about physical accuracy. But I do believe that it would be a nice starting point for each scene if I can be able to understand the logic.

[stevesideas]

I usualy put a grey128 material on all objects and make lighting. I try to get the medium grey in render out put too. Then I put 225grey for white and increase lighting only a bit. And then try to put proportional values for all materials in between.

I am sometimes confused about physical accuracy. The reflactance value is also how much light is bounced in real life- am I wrong?
So then do we need to put reflective materials (maybe even fake reflective values) so that light bounces off more and get brighter renders?

I can never decide which approach is better. And honestly I really feel mixed up. So I always give up about physical accuracy. But I do believe that it would be a nice starting point for each scene if I can be able to understand the logic.

If you use your method dont you encounter problems with exposure ? If you have the exposure set so that the rgb values are around 128, isnt your sky very dark ? (If using vraycam exposure). If you have dont affect background (when I tried), the background was pure white and the building looked very gray still even if I put the sun multiplier up to 1.4)