mental ray 102: Lighting Part
2 Jennifer O'Connor College of Lake County Part 2
Updated: October 2008
Jennifer O’Connor
College of Lake County, Grayslake, Illinois
joconnor at clcillinois.edu
jenni at 4DA-inc.com
There are a number of new features in the new mental ray version 3.5 and 3.6 that make it easier to make great renderings. We’ll take a look at a few of the new features, and some of the things I’ve been using a lot lately.
There have been a lot of things written about mental ray, and I’ll try not to duplicate too much here. My goal is to be succinct, to cover some of the essentials to give you an overview, and get you going with this powerful renderer in 3ds max 2009.
For more details on these features I highly recommend two books on the subject, "Rendering with mental ray & 3ds max" by Joep van der Steen, and "Realistic Architectural Visualization with 3ds max and mental ray" by Roger Cusson and Jamie Cardoso.
I also recommend the training videos at www.mentalboutmax.com. They are very well done, and very affordable.
The files used in this document are at http://www.4DA-Inc.com/mentalray/index.html. The 'Light Gallery' scene is a slightly modified version of a mental ray sample provided with 3ds max. For the Exterior scenes, the file 'Houston.max" is available on the site.
In Part One we looked at the general features of the renderer, and Indirect Illumination using Final Gather. In Part Two we look at Lighting and Materials, including the new Daylight System, Sky Portals, the Arch & Design materials and , including the Indirect Illumination technology of Ambient Occlusion.
Contents
mr Physical Sky ENVIRONMENT MAP
Sky Settings within the
Daylight System
Exposure Control with the
Daylight System
Color (Gamma) Correction
with Daylight System
Photometrics in 3ds Max 2009
Design
if you are using 3ds Max 2009 Design, then mental ray is already your default rendering system. If you are using Max 2008 or earlier, however, you must set the current session of 3ds max to use mental ray. You need to either change the renderer to mental ray from within the Render Scene dialog (F10), or choose a render Preset that includes mental ray, or go to the menu Customize->"Custom UI and Defaults Switcher..." and choose a mental ray setting. Using that last option changes a number of things in 3ds max to automatically use mental ray materials, mr Daylight system, and sets mental ray as the renderer:
This following discussion will assume that this setting
change has not been done, and that you need to choose the mr materials and
other settings manually. This will
assist you in finding these options, and changing existing scenes. We certainly encourage you to use these UI
settings to make the use of these tools more straightforward.
A Daylight System is an object that combines two lights that simulate the illumination of the Sun and Sky for a particular place, date and time. It greatly simplifies outdoor lighting set up, and produces exceptional results. The mental ray lighting used in a Daylight System simulate physically real outdoor illumination - the Sun is the intensity of the real sun - and allows for physically-real direct and indirect lighting effects.
The Daylight positions the Sun in the sky based on its settings for Time, Date and Location. Time and Date can be animated to produce Sunlight Studies, showing the position of sun and shadow over the course of a day.
The basic procedure to create Daylight: Create, Rotate, Time & Place, mr-ize it, Sky, and Exposure:
1. Create the Daylight System: Select Create->Systems->Daylight, then click and drag in the viewport to place a Compass Rose, moving slightly to set the size of the Compass Rose, then release and move the mouse and click again to set the Orbital Scale offset of the light Assembly. Choose Yes to any pop-up dialogs.
2. In Modify tab, ensure the lights in the Daylight system are mr Sky and mr Sun. Choose Yes to any pop-up dialogs.
3. In Motion tab, change the Location and Time/Date of the Daylight object to match your scene and desired Sun position in the sky.
4. In Motion tab, set the Compass Rose to your scene's North direction.
5. Set the Environment map to use the mr Physical Sky shader. (Press 8 for dialog).
6. Use the new mr Photographic Exposure Control and not the Logarithmic exposure control. (Press 8 for dialog).
When you create the Daylight System, you may get a dialog that asks if you want to use the mr Photographic Exposure control, and set it to a daylight setting of 15. Saying Yes to this is fine. (You will also want to change the Environment Background to the mr Physical Sky map type once you are done with creating the Daylight object, and may see a dialog prompting you if you want to do that during creation).
In the Modify tab, you'll see an object called "Daylight01", and in the stack you'll see the base object "DaylightAssemblyHead", along with the settings for the Sun and Skylights. You'll find settings for the Position and Time of Day for the Daylight object within the Motion tab.
Again, ensure that the Sunlight and Skylight drop-down menus are both set to the mr Sun and mr Sky options, respectively. If you have your UI Defaults set to mr, then this should be all set.
Clicking on the Position's 'Setup...' button just brings you to the Motion tab, where you can change the Date, Time and Location.
A little about Assemblies
An Assembly, such as the Daylight Assembly Head, is typically a combination of Geometry and Lights combined into a new 'assembly' object, similar to a group. When you create your own Assemblies from the Group->Assembly pull-down menus, you will have a group-like object with a handy Multiplier setting within the Modify tab you can use to set the intensity of the light.
The Daylight assembly is more sophisticated than a normal assembly object, and consists of a Compass Rose, a Skylight object, and a light to represent the Sun, and a number of settings for both lights.
3ds max 2009 now has the ability to set the position and intensity of the Daylight System based on a Weather Data File, provided by the US government, going back many years and to various points around the globe. The default option is to have you set the location and Date/Time yourself, and not to use a weather file.
Settings you will want to use:
Usually it is important that the lighting reflect reality for your outdoor scene and its position on Earth, so one of the first things to do after creating the Daylight object is to click on the Get Location button, and select a location close to where your environment is located. (This is found in the Motion Tab when the Daylight object is selected).
When the "Geographic Location..." map dialog opens, click on the map to set the location to a city nearby. If your part of the world is not shown, you can choose a different location from the Map drop-down list, or you can choose a Lat/Lon location in the settings to specify a point on the Earth.
You also want to make certain that the compass rose is pointed towards the North Direction of your scene. By default North is pointing in the positive Y direction of your World Coordinates.
Let's take a look at the essential settings in the Modify Tab...
If you used the UI switcher and one of the mental ray options, or use Max Design, then the default lights for the Daylight object are the mr Sun and mr Sky. If not, then the default light types for the Daylight system are a Standard (non-photometric) light for the sun and a standard Skylight for the sky, and you will need to change these lights manually to the mr Sun and mr Sky light types.
In the Modify tab image below, the Sun and Sky were switched from Standard lights to the new mr types, and once the Sky was switched to mr Sky, the dialog shown below-right pops up to ask if you want to use the 'mr Physical Sky' map for the environment in your scene. Choose yes, and we'll go over what this is in a little bit.
Again, if you used the UI switcher to select a
mental ray UI,or are using Max 2009 Design, then going to the Modify Tab will
show that the Daylight system is already set to use the new mental ray mr Sun and mr Sky . You may still get the mental ray mr Sky warning when creating the
Daylight object.
The
nice thing about using the mr Physical Sky is that the background sky image will
change based on the time of day and position of the sun.
Settings you might use:
· mr Sun Photons
o Use Target: Enable the use of the Radius setting.
o Radius: This value allows you to focus photons from the sun into a specific area (radius) around the target for the light. This is an optimization, and is used, for instance, where you use the mr Sun to produce light for an interior scene; you don't need photons throughout the outdoor portion of your scene, and can focus them through a window, for example.
o Photons
are needed for GI and Caustics, but not for Final Gather.
·
·
· The CIE sky model is another industry-standard physically accurate sky representation. It has settings for Overcast (default) or Clear Sky. I usually change this to Clear.
Settings you might want to use:
·
· For CIE Sky: Turn on the Clear Sky option if needed - Overcast is the default - or your scene will seem dark. I usually keep the other settings as-is.
· For CIE and Perez: I usually leave the options for the Diffuse Horiz and Direct Normal illumination as-is. Note, however, that these are animatable if you aren't using a Weather Data file.
· Haze: For Haze-driven model. Basically, 'Smog' in the air, default 0.0 and maximum 15.0. Creates a yellow tinge that gets deeper as you look further into the distance. Affects the overall sky and the rendered object colors, and makes me wheeze a bit.
· Horizon: A general Sky setting for all. This group creates a colored ground plane and a fuzzy 'horizon line' terminator between the ground plane and the sky.
o Height: Vertical position of the horizon line, which affects not only it's appearance in the sky but also the position at which the sun 'sets'. You can compensate for your point of view, so if you are at a high elevation and the horizon is below you, you can move the line with a negative value. A slight negative value can remove the horizon from most scenes at ground level.
o Blur: Adds a slight blur between ground and sky. 0.1 is default, and 0.0 is a sharp line. Useful up to 0.5.
o Ground Color: This should be set to an average color for your ground plane. It represents the 'floor' of your environment, and affects the color of the horizon line. If you do not have a ground plane in your scene, this color is visible in your environment, generates reflected illumination, and affects the lighting and color of your scene.
· Aerial Perspective. This is the fuzzy horizon that is added to your background image. This is usually fine if you are using the mr Physical Sky map for your environment, but will Not look correct if you have a bitmap there. I'll turn this option off when using a background image.
One of the great things about the mental ray flavor of the Daylight system is that it can control an environment map type called "mr Physical Sky". With this Environment map, as the time of day changes in your Daylight system the environment map sky in your renderings will adjust accordingly both in intensity and color. You'll even have a sun disk properly positioned in the sky, and the sky will glow brighter where the sun is located, and fade and change color appropriately as the sun rises and sets. You can also get simulated haze effects which interact with the light effect from the mr Sky light.
The disadvantage to the mr Physical Sky is that there are no clouds, however it does support custom environment maps with some caveats.
As we saw earlier, 3ds Max may automatically prompt you to add the mr Physical Sky map to your environment settings when setting up the Daylight system to use the mr Sky. This map can also be added in the usual way, via the Environment settings (press 8 for dialog).
To examine and edit the settings for the mr Physical Sky (or any environment map), you must bring it into the material editor:
· Open the Environment Dialog and the Material Editor at the same time.
· If it isn't already, set the Environment Map to the mr Physical Sky map type.
· Click and drag the map button from the Environment and Effects dialog to a sample area in the Material Editor, and create an Instance type.
Instancing the map allows you to change settings in the Material Editor and have the changed reflected in the Environment. You'll find many map types in max that can only be edited by dragging them into the Material Editor.
Generally, the settings are set to use what has been configured within the Daylight system, and there is not much here to tweak. Let's assume you'll keep this configuration as we are only covering the essentials and not the little-used details. :)
Settings you might use:
In the "Sun Disk Appearance" section you can change the size of the sun (Scale), the intensity of the disk, and the surrounding glow. The sun is overly-large by default, and usually that looks pretty good.
Decreasing the Intensity can give the effect of a dense atmosphere, blocking some of the sun. Decreasing the Glow will make the atmosphere look crisper, as with less diffraction of light.
These are all 6am in San Francisco. The Custom Background Image, as you can see, eliminates the appearance of the Sun and Glow in the rendering, and the color and intensity will not automatically match the Daylight - you'll have to make adjustments. Background image maps may also need their "RGB Level" multiplier increased in the bitmap Output setting for it to be visible. (These are in the settings for the background bitmap, not the mr Physical Sky)
Using a custom background image is the only way to get static clouds in your scene. A bitmap RGB Level setting of 150+ is not uncommon for non-HDRI images.
Also be aware that the Custom Background is only visible as a background in the rendering, and reflections will still be of the physical sky.
Adjusting the Daylight to a daylight time of the day will give you a clear blue sky with the default mr Physical Sky settings:
As you can see, the Sun and the glow around the sun are present (as seen in the reflections), and moved into a position correct for noon, in this instance. No custom background is used.
The other settings that are available are found within the Daylight System, and similar settings are in the mr Physical Sky map. For simplicity we'll assume you'll want the mr Physical Sky tied to the Position, time of day and other settings of the Daylight assembly.
There are two exposure controls you should consider, the Logarithmic and mr Photographic Exposure controls. Personally, I stick with the mr Photographic Exposure Control for all mental ray work.
· Here are the Logarithmic Exposure Control settings I use with a Daylight System:
o Make sure that the Exterior Daylight checkbox is turned on.
o Set Brightness from 50 to 55. The default 65 is too washed-out, IMHO.
o Set Contrast to 75-80. The default of 50 is too low.
o You can change the Color Correction – which is similar to a camera's ‘white balance’ setting, to shift the colors and help eliminate some of the bluish tint that you get from the sky.
o Optional is to adjust the Mid-Tones down slightly.
o Change the Physical Scale to a number between 80000.0 and 100000.0. Changing this setting scales up any non-physical lights to be in the correct scale for the brightness of your scene, but also has a huge impact on any HDRI bitmaps that you use in the Environment settings of your scene. It does not affect non-HDR images in the Environment. I usually use 90000.0 or 100000.0 for this, as it is the intensity range of the sunlight.
o The checkbox for "Process Environment and Background Maps" only affects HDRI images used for the background/environment.
One disadvantage to the Logarithmic control (compared to the mr Photographic Exposure) is that the Daylight option is not animatable so you cannot go from outdoors to indoors easily.
Also, because the Logarithmic control does such a good job shifting your rendering into a usable color range, it is easy to produce a greatly over or under lit scene without realizing it. Overly-bright lighting ends up pushed down to a moderately bright range, and an under-lit scene is shifted upwards. It is not smart about the use of Gamma when that is enabled in Max.
The advantage to the Logarithmic control is that it is faster than the mr Photographic.
The mr Photographic Exposure Control was introduced recently in 3ds Max, and includes both camera-like exposure controls such as f-Stop, Film ISO and Shutter Speed, and also a simple 'Exposure value' that is the end-result of the other three variables. There is a preset drop-down menu where you can choose from setting such as "Physically Based Lighting, Outdoor Daylight, Clear Sky" all the way down to "Physically Based Lighting, Indoor Nighttime" and even "Non physically Based Lighting".
· Certainly, the easiest thing is to start with a preset from the drop-down menu, and then tweak values from there. That gets you in the general range.
· The radio-button for "Photographic Exposure" may be set, and you'll be tweaking Shutter Speed, f-stop, and ISO. Make your life easy and switch to the Exposure Value (EV) option (shown at right). As you render scenes you'll figure out what values work best for you, up-or-down from the presets.
· I usually use 14.5 for an outdoor scene, but might use even lower if using a Perez or CIE sky model.
· Indoor scenes can be anywhere, based on your lights. If your scene renders black, then start at 0.5 and see what you get.
· The Highlight (Burn) created blooms around very bright lights and reflections. Tweak this down a bit if needed.
Gamma correction compensates for differences in color display of various devices, including CRTs, LCDs, printers, and scanners. Their color inputs and outputs are not linear, and to produce correct results the colors need to be shifted based on a Gamma correction value. Every device will be slightly different.
Settings you will use:
As a rule you should set your display Gamma in Max, via the Customize->Preferences and the Gamma and LUT tab. Enable Gamma/LUT, and choose the Gamma option. Adjust the slider value until the inner and outer square are about the same intensity:
As you can see above, my monitor's Gamma setting is 2.07 and for me the two squares look about the same inside Max, yet in this printout the two squares are very different. Different Gammas and very different results.
The other two highlighted setting groups at the Input Gamma and Output Gamma values, and the Affect Colors and Affect materials options. It is generally accepted that setting the Input and Output to 2.2, and enabling the Materials and Colors options, is a good idea. I have used settings from 1.6 to 2.2. With my monitor at 2.07, an output value of around 2.0 would look the best for me.
Input and Output
Gamma Settings
You will find with the Daylight System that many colors get very washed-out looking in the process of rendering. This is because photographs of materials, for instance, are already photographed in bright lighting and are most likely gamma corrected to look good on your monitor. The Input Gamma setting will shift these back to where they need to be so that the colors render correctly and are not overexposed.
If you use Targa images that contain Gamma information, you may have to set the Gamma inside the Bitmap parameters in the material editor to use the Inverse (1/gamma) value. You find this in the File dialog when selecting the file on your drive.
The output Gamma setting shifts the colors to a range that will display well on computer displays. A value of 1.8 is fine for computer displays, but 2.2 is common for video. Without this setting, images you put on the Internet or share with others will generally be too dark.
Figure 1: Comparison
between Input Gamma =1.7 (left) and Input Gamma=1.0 (right) (logarighmic
exposure).
A 2.2 Input Gamma will darken the grass bitmap even more (mr Photographic Exposure w/o cloudy sky):
The settings with these lights that are different than other Standard lights are within the 'Area Light Parameter" roll-down, as shown at right.
The "Show Icon in Renderer" option obviously makes the light object visible in your rendering, and also produce realistic highlights in your reflective objects.
U and V samples are the number of lights in an array to make up the area light. Since we ct that area, we have to pare that down. Incresent that area, we have to pare that down. Increase this value if you are seeing uneven results in your renderings.
An Area Omni light can be a Sphere or a Cylinder, and an Area Spot can be a Disc or Rectangle. Here is a Cylinder (on right) that is visible in the rendering: