作者：Jelmer

原文地址：http://www.enjoycg.com/forums/enjoycg-tutorials/2180-mental-ray-lighting-rendering-tips.html

 

Do you know how to light and render your models well?

Often I tend to spent more time playing with lighting and rendering than actually modeling, it's fun and increases the realism of your artwork. I think lighting has the largest influence on your renders, yet it's underestimated by many 3d artists, So that's why I've written this article. The tips below should help you improve on lighting and rendering quickly.

Another important consideration is the link between lighting and shading (materials), Especially reflective and bump materials are affected by lighting a lot, so if you want to have a realistic result you should experiment with shading and lighting at the same time. So let's get started with some basic tips, tricks and ideas! Take a look at the renders below, of the exact same scene, if you're not convinced yet.

 

Keep it simple.

 

First of all, you shouldn't make things more complicated then you need to, usually a few lights are enough, with the right settings, I hardly ever use more than 2-3 lights for basic scenes, although there are always exceptions to the rule. For example you might need a lot of artificial lights in a city scene. Also, if it's not needed, don't mess with (final gather) settings too much, most of the time the presets work fine, for exteriors don't forget about logarithmic exposure control set with "exterior daylight" when using the daylights system.

 

Tip: If you have a few lights in your scene and want to know how they affect your lighting, give each a unique, bright colour so it's easy to spot which light does what!

Final gather & Global illumination

 

Are two very useful rendering techniques to make shadows a lot more realistic, without them shadows tend to be one plain colour (black mostly) yet you hardly see this happen in real life, so it shouldn't happen in your renders either. All the renders in this article use final gather, keep on reading to learn how it works.

 

Basically mental ray calculates the light/darkness of a shadow by shooting out rays of lights (photons), which bounce of surfaces in a realistic way, in max 9 it's very easy to setup, just press f10 and turn on final gather, try the draft preset, set bounces to 1 or 2 and that's it, your render should look a lot more realistic.

 

Of course that's just the basics, I would suggest having a look at the max reference file for more advanced tweaking and GI rendering principles.

Add colour

 

Some 3d artists tend to forget that light is hardly ever pure white, Artificial light can be almost any colour but is most often tungsten (orange-ish) although they might appear white to you, they're not! Sunlight colour varies depending on the time of day, but colours tend to get more visible near sunrise and sunset, sometimes even becoming bright red, pink or purple.

 

Often you will need more than just a sun, because the atmosphere/sky also emits light. The colour of the sky is similar to the colour of your skylight, so this obviously depends on weather, if the sky is clear, it will be blue, on the other hand overcast conditions tend to be more gray.

A system that will "colour" your lights automatically in 3ds max with mental ray is the Daylight system, set it to custom, lower the sun's positions and colours will become more intense, usually orange, an appropriate environment is also created for reflections with the mental ray physical sky shader, which saves some work again. The only downside here is you lose some control, sometimes you might need more extreme colours.

 

A simple and clean way to render an object with standard materials applied is using 2 lights, in different positions in relation to the object, with different colours, try blue with yellow/orange for example. Of course you're not restricted to a few colours, because it's CG, you have the power to change anything you want, be original and try different colours you wouldn't usually use, just have a look at the image below, and the HUGE difference, the 1st render looks so much more natural!

 

 

 

Tip: Use colour to evoke certain emotions and atmosphere in your artwork, also don't forget about post render edits, use photoshop to alter the colours quickly, without the need to re-render! Try image > adjustments > variations, image > adjustments > hue/saturation. If you have some experience with editing your photos, try applying the same techniques. If you're going for photo realism, don't forget to add some noise and imperfections (ISO noise?).

Soften those shadows

 

By default, mr (mental ray) Area lights have raytraced shadows on, unfortunately they're perfectly sharp, again, this hardly ever exists in real life. To fix this, I always use Area lights, as the size of a light increases, so does the softness of shadows, it's very logical, plain physics. When you do this, make sure you increase samples, 15 - 15 produces great quality, with longer rendering times of course. If the soft shadow area is small, you can get away with lower samples though. Because a large light emits rays from different points, the shadows will also be spread, the further apart, the more this happens, the distance between the object creating the shadow and the object showing the shadows also affects the result, try moving your hand in front of a light and changing the distance for a different result, and a render to show the result:

 

 

Don't forget about decay!

 

Especially artificial lights decay quite quickly, the light they emit gets weaker with distance, finally losing all it's value/energy. In night scenes you can use this to increase the brightness of just a certain area, emphasizing it's importance, and increasing contrast. You can adjust the setting of decay in each light, play with the settings to see what happens, as always. Here's a comparison between different decay settings:

 

 

 

Tip: Try using decay for streetlights, add the main character/point of interest under the beam of light produced by the streetlight. Decay also works well combined with volume light and glow, really focusing the light on just a part of your image.

perfection is unrealistic

 

This tip can be applied to many areas of CG, and 3d in particular. In reality, nothing is perfectly straight, clean and has 90 degree angles, if you're models are like that, it won't look right, because we're not used to perfect objects, simply because they don't exist. Adding some very subtle noise, along with good lighting will give you some very subtle shadow play even on flat surfaces, make sure a mesh is dense enough before applying this (add some turbosmooth first). In the example below I haven't changed the lighting, but the lighting does affect the result a lot, because the light in this scene is positioned so low the very slight noise will be well visible due to the shadows it creates.

 

Chamfer your edges, with spectacular specular results

 

This helps to get rid of the perfection, see the paragraph above for more on that, but also affects shading a lot. A regular box will hardly have any specular reflections because there are no right angles for the reflections to occur, by adding a chamfer the specular highlights "hit" the chamfered edges and create a far more realistic result. Besides improving specularity and reflections, shadows will also look a lot better, and objects on top of each other will have a shadow in between them, so they don't appear to float.

 

Sometimes chamfers don't work well, or take too much time on a complicated model, since max 9 there's a solution to this problem though! Mental ray A&D (architectural and design) materials have this built in, under special effects > rounded corners, neat huh? So without edits this only works with A&D materials, fortunately Jeff Patton has posted a fix for this, so you can also use it on all other mental ray shaders (scroll down half way the page) see the render below for the results:

 

 

 

Position Matters

 

The position of lights in your scene have a huge influence on the resulting render, distance and direction in particular. I always create a camera when I start rendering a scene, first get the right composition in your perspective and press ctrl+c to create a camera in the exact position. Then I usually add lights in the top viewport, because you have a visible camera you'll see the position and angle of the lights in relation to the camera, which really affects lighting a lot.

 

Never place your "main" light behind the camera, you will hardly see any shadows and the resulting render will look very dull, with little contrast, The whole area around the camera is no good for lights with one exception, fill lights, which you can use to lighten the dark shadows created by your main light.

 

Most of the time I add my main light(s) at a right angle to the camera (90 degrees) approximately, Of course this is not an exact science, you should play with the positions to see what happens, it also depends on the shape of your model of course. You will have obvious shadow, and a nice amount of contrast, with your model well visible.

 

If you want even more contrast, or just a black contour of your model, place the lights behind your main model, with the camera in front, you'll often see this in real life, looking towards the sun at sunset.

 

 

 

Another nice effect is to position your main light above your model, creating a nice clear shadow on the plane/object below your main model, basically the street light idea again, finally you should try to be creative yourself, experiment and see what you can come up with.

 

Focusing with Depth of field

 

Depth of Field (DoF) is another useful rendering feature, not so much about lighting but it does have a huge influence on the realism of your work, it's also very useful to focus the eye of the viewer on a certain object in your scene. I became more aware of this technique after taking photos more regularly, especially digital slr's with manual focus and Aperature value settings are nice to play with.

 

Basically there are two important settings, first of all you can adjust the size of the depth of field, and then the distance which is in focus. Of course you want to have your main subject in focus most of the time, and if you have objects far away and close to the camera, you can really add a nice touch to your image, the downside of DoF rendering is render time, as always . There is an easy way around this though, Most of the time I render a Zdepth pass and then use that in photoshop to play with settings, it's a much more flexible and faster approach, take a look at this excellent tutorial on DoF for the details. Below is an example, it's overdone I guess, but it does show the effect of DoF:

 

 

 

Resources:

• jeffpatton (blog, with great tips!)
• Mymentalray - mental ray forum

Coming up next

 

An article about adjusting and improving your renders with photoshop. You've waited patiently, for hours maybe, but with a few minutes of work you can take that render to the next level, or fix a mistake that might take ages to fix if you need to re-render, also, if you have any ideas for an article they are welcome.

 

I hope you enjoyed reading this article, if you have any ideas and/or comments feel free to post them below. if you've done any renders with the tips from this tutorial, I would really like to see them posted below .