Neutral Lighting Rig
By Neil Blevins
Created On: Sept 24th 2013
Updated On: Sept 27th 2013

A Neutral Lighting Rig is a light rig where the color of your material is identical to the color it produces in the final render. So if your material is 50% grey, its result in your render should be 50% grey as well. A neutral lighting rig may not produce the best looking images, but it's a good sanity test to make sure your colors are working properly, your materials are working properly, and if you test all your assets for a project with the same rig, you can get a consistent result. So if you're working with a big team of people shading a lot of assets, have each asset run in the same neutral lighting rig, and that way you can compare the results. Years ago I worked at a company that didn't have a neutral lighting rig, and each artist made up their own rig, and the result was when you put two models together in the same lighting, they didn't match at all, and we have to reshade or retexture a lot of stuff.

For this tutorial, I'll be providing 3 rigs in vray 2.40 for max 2011 (These files also need Cuneyt's ColorCorrect plugin). Even though the files are vray specific, the theory is identical for any renderer, and it's not too hard to setup your own rig in whatever renderer you'd like. I'm also using Linear Workflow.

Download the rigs here: neutral_lighting_rigs.zip

The three rigs will be...
Also note, this is certainly not the only way to make a neutral lighting rig, this is just my preferred way and I think it gives the best results. But feel free to violate any of the rules I give below if you feel you have a good argument for doing things differently. In some ways, the most important thing is to use the same lighting rig on all your assets, the rig itself is more open to interpretation.

Rig A: 3 Point Lighting

Here's my first rig...



This rig consists of an area light for the key (front upper right), an area light for the kicker (behind middle left), and a skylight for the fill (0.2 intensity). So it's a variation of the classic 3 point light setup. GI is turned on with secondary bounces. The robot head is approx 6 feet tall. The robot is also shaded 50% grey like the second sphere.

Here's a general idea of the placement of lights...



Notice the 4 spheres in the image. These are my reference spheres. The first sphere (lowest) has a final color of 25% grey, the second has a final color of 50% grey, the third is white, and the fourth is a fully reflective ball. Since I have no environment in the scene, the reflective ball appears black with some tiny hints of the other balls and the robot head in the reflection.

Note, 50% is the final color after your final gamma correction is applied (this happens because I'm using Linear Workflow). It's un-corrected value is 18%. If you're into photography, you may have heard the term 18% grey card? That's where it comes from, 18% is the uncorrected value for 50% grey, or middle grey as its sometimes called.

Also note, obviously, not every point on your model is the same color as the input texture/color, some are darker. Otherwise, there would be no shading or shadows to your image. For some people, the mid color of your image should be the neutral color. But for me, I like the brightest color on your model to be the neutral color. So if you color pick the brightest parts of the model, those should be the correct color.

Rig B: IBL and Area Light Sun



The second rig is an IBL (Image Based Lighting) of a street for fill (skylight), and then a area light for the "sun".

While the skylight isn't 100% neutral (since the hdr has some color to it), I desaturated it a lot, so it's almost neutral light. Feel free to desaturate it all the way if you'd like.

Rig C: All IBL



This rig is all IBL, and the sun is part of the hdr image, instead of being a separate movable area light. Provides obviously blurrier shadows since it's all diffused light.

Feel free to replace these IBLs with hdr images of your own. Just remember to increase or decrease their brightness so you get neutral color and true value. Also, if your IBL has a sun or another super bright spot, make sure to align it so its facing the front of your model. The max files have a camera specifically so you can place the sun in the right spot.

Pretty Rig

As I mentioned before, these rigs don't produce "pretty" results, but the results are consistent. But feel free to modify the rigs to make prettier rigs that show off your model when you want to impress the client. But also check your model in these boring rigs to confirm that your colors and materials react as expected.

Here's an example, I tinted the sky blue, the sun yellow, made the sun higher to get deeper shadows, and made the sun brighter to blow stuff out a bit.



Reflectance of Human Skin

Also note that when choosing colors for your objects, Caucasian skin is thought to be somewhere in the range of 30-35% grey in uncorrected value (58% after gamma correction), so its brightness should be somewhere just a little brighter than the 2nd lowest sphere in any of these neutral lighting rigs. That info may help you calibrate your material colors. In general, the colors of real world objects are a lot darker than you may first guess. It's the lighting that's brighter than you may expect which leads to your final bright values.

Alex McLeod also gave me this tip on the subject. While skin color varies with race, eye whiteness doesn't. So another good test is that the white of the eyes tend to be about 50% grey in uncorrected value (73% after gamma correction). So that's about halfway between the 2nd and 3rd sphere. From there you can also calibrate the skin color depending on if the eyes seem too bright or too dark for your skin color. Thanks Alex!


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