10 key tips for lighting and look developmentPhotorealism is both my professional speciality and my personal passion. I like to observe thenuances of natural phenomena so that I can trick an audience into forgetting that what they arewatching is CG.

In simple terms, what we do is make believe, and because we dont have the tools or computingpower to reproduce all of the detail present in nature, we have come up with certain tricks to achievea similar effect.

Here are a few tips technical directors like me use every day to overcome the curse of the CG lookand to streamline the process of lighting and look development for characters and environments.

A simple look development environment. Keep look dev and final shot lighting separate.

1. Keep the look dev and lighting separateDont look dev your character in the shot: its too distracting. If you dont have reference footage shoton a practical lighting stage from which you can extract the lighting information, create a neutral lightrig with a key, rim, fill (all white) and a sky dome (like a sky HDRI). Dial your materials and texturecorrections for all your characters into this rig so that you can ensure consistency between them. Usethe rig for all your look dev work or, if you have time, create different rigs to test how yourcharacters hold up in extreme lighting situations.

Before moving into colour, test models with a simple gray material applied to refine bump anddisplacement.

2. Test your displacement with gray-shaded materialsGood displacement and bump maps will get you a long way towards achieving realistic materials. Butit can be hard to evaluate their effect when viewing a model which has diffuse and specular texturesapplied so create overrides on your materials (or render modes in Maya) to turn off diffuseroughness and spec maps. You should be left with a plastic-looking grey material which will help youdebug all your displacement issues.

No real surface is completely smooth. Use roughness maps to simulate microscopic naturalirregularities.

3. Use spec and roughness maps to simulate surface irregularitiesIn real life, even the smoothest of surfaces be it a car paint or a mirror will exhibit variations in theway it reflects light. Things like fingerprints, the direction in which the surface was wiped and slightfluctuations in the coating will cause surface irregularities that can be simulated with roughnessmaps.

Similarly, bear in mind that objects dont always reflect the same amount of light in every direction.For example, when dirt accumulates in creases on a surface, it reduces their reflectivity. Thisphenomenon can be reproduced with spec maps. Variations in spec maps is the key to creating trulyphotorealistic materials.

Even if the final render will have a limited tonal range, always create color maps at full dynamicrange.

4. Always paint non-color maps with the widest dynamic rangeNon-color maps such as spec, roughness and even bump should be painted with the highest dynamicrange possible (so whites have a value of 1, and blacks of 0). Even if this seems too extreme for theeffect youre searching for, if you limit the dynamic range from the start, once you start pushing thesemaps around in the material, youll get clamping and banding. If a map has an adequate dynamicrange, you can always compress or expand it to give you the desired range in the material later on.

Using linear color space throughout your pipeline takes getting used to, but produces superior results.

5. Use linear color space all the way!Color space is a hot topic in the industry, and at present, the way to go is linear all the way. [If you'renew to linear workflow, Greyscale Gorilla has a good overview, including links to more detailedarticles - CGC.]

Always export your maps in linear color space, and work in linear mode in your renderer. Its alsogood practice to export your displacement and bump maps with a depth of 16 bits or more. Thenrender your images in linear format (as EXRs or linear TIFFs, for example) with a minimum of 16 bitsso you have maximum flexibility in comp. Compositing packages like Nuke and Flame work in linearspace, so if you work this way, youre linear from start to finish, giving you the freedom to output inany format or bit depth you want.

One of HDR Labs free sIBLs. Use textures like this to break up the regular spec patterns of CG lights.

6. Use textures on your lights, with falloff and no sharp shadowsWhen you are lighting a scene, always use textures on your CG lights to break up the even specularpattern. You can find some free maps online (for example, HDR Labs sIBL archive) to plug into yourdigital versions.

Another thing that sounds obvious but always creeps up in amateur CG renders is sharp shadows. Inreality, light sources are not single points in space, and even light rays from those that arenear-infinitely distant such as the sun are refracted by the atmosphere. Therefore, always tweakraytraced shadows on your spot and point lights so they arent perfectly sharp. Also, always userealistic decay in your lights. No decay, perfect specular patterns and perfectly sharp shadows areinstant giveaways of CG renders.

Simplicity works: outdoor shots on Green Lantern use only a sky dome and single directional light.

7. Simplicity is key in big environmentsUnless you are in a fantastical alien environment, outdoor scenes are usually lit by the sun and thesky alone. So use only a directional light and a sky dome to achieve that natural look. Highlights areusually defined by the color of the sun, and the shadows will usually be influenced by the color of thesky. To get the most out of this simple but effective lighting scenario, always use global illumination.GI is the bread and butter of photorealism.

For the large shots of the alien planet in Green Lantern, I used only a sky dome that was colorcorrected and a directional light. The color difference in the sky dome was enough to give theresulting renders that alien feel.

Layered materials lend realism to the CG walls in this shot from The Amazing Spider-Man.

8. Know when to use layered materialsAs much as people fear them, layered materials are super-useful in getting certain looks. Things likecar paint, polished wood floors and lacquered surfaces consist of a base coat covered with a clearcoat that gives them their shiny appearance. Even skin can be simulated in this way.

In most cases, a layered material with a rougher base material that defines the color and base specunder a fully refractive shinier clear-coat material with spec alone will give you great results. (Note:when you are using layered materials, make sure that your specular values for the two layers add upto 1 for example, 0.3 for the base coat and 0.7 for the clear coat.) On The Amazing Spider-Man, weused layered materials on all the walls and floors in the high school to achieve a polished look.

Relighting in Katana. Even if you dont use specialist relighting tools, render lighting elementsseparately.

9. Render out lighting elements separatelyEven though lighters want their renders to be perfect out of the box, there are always things thatneed tweaking in the comp. Things like changing the light balance, adjusting specularity or justgetting good mattes are only possible if you render out the lighting elements as separate passes.

At Imageworks, we always render spec, diffuse, separate lights, mattes, Z-depth, GI, point and normalpasses by default. These are also great for debugging shots: for example, identifying what anindividual light is doing, or determining the relative contributions of indirect and direct specularity toa particular highlight.

Photographic reference was the key to achieving the realistic-looking posters in this shot fromSpider-Man.

10. And remember: use reference material!I cant stress this enough. Even if youve been dialling materials over and over for years, you stillalways miss out something that makes the result look absolutely real. You can only pick up thesesubtle details by comparing test renders to real-life reference material.

For example, on Spider-Man, we had to place hand-made posters along a CG hallway. It sounded asimple job but it proved to have so many intricacies (the difference in shininess between the markerdrawings and the surrounding paper, the variations at the corners of the posters, and so on) that wednever have been able to achieve a good result if we hadnt had good photographic reference.

Cosku Turhan is currently Senior Lead Technical Director at Sony Pictures Imageworks,where he has led teams of artists on Green Lantern, The Amazing Spider-Man and Sam Raimisupcoming Oz: The Great and Powerful. A graduate of Bilkent University and USC, he also worked atVanguard Animation as a character modeller and rigger.