WEEK 12 HANDOUT
Arnold Renderer
Arnold developed by Solid Angle is an advanced cross-platform rendering library [API]. Today, it is used by various studios in film, gaming, animation, and broadcast industries across
the globe. This unit introduces you to the MAXtoA plugin. MAXtoA is a plugin for Autodesk
3ds Max which provides a bridge to the Arnold rendering system from within the standard
3ds Max interface. Arnold was designed to easily adapt to the existing pipelines. It can be
extended and customized by writing new shaders, cameras, filters, custom ray types, user-defined geometric data, and so on. The primary goal of the Arnold engine is to provide a
complete solution as primary render engine for animation and visual effects projects.
Arnold Render Sampling
Arnold is a raytracing renderer. Sampling and ray depth are one of the most
important settings for the Arnold raytracer.
In order to produce a rendered image,
Arnold needs to know color value of each
pixel. To do so, Arnold fires a number
of rays from the camera and then they
hit objects in the scene. When rays hit
something in the scene, they calculate the
information about the surface and return
it for processing. This process is called
sampling.
Sampling and Ray Depth
The Sampling and Ray Depth settings are
available in the Render Setup > Arnold
Renderer panel > Sampling and Ray
Depth rollout. These settings control the
sampling [image quality] of the rendered
images. Increasing the sample rate removes the noise from the rendered images but at the expense of the increased
render time.
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The actual number of samples is the square root of the specified value. For example, if you
specify Camera (AA) samples as 3 [AA=anti-aliasing], it means that 3x3=9 samples will be
used by Arnold for anti-aliasing.
If you specify a value of 2 for the Diffuse Samples, it means that 2x2=4 samples will be
used for global illumination. The same is true for other settings as well.
The Camera (AA) setting can be considered global multiplier for all other components:
Diffuse, Specular, Transmission, SSS, and Volume Direct because for these components
sampling rates are expressed for each Camera (AA) sample.
For example, if you specify Camera (AA) value as 3 and Diffuse as 2, the total number of
samples per pixel used will be 36 [(3*3)x(2*2)].
Preview (AA) Samples
It controls the super-sampling value for previews. It affects the quick first frame before the
actual super-sampling starts. The default value for this setting is -3. Negative values
sub-sample the render therefore allowing faster feedback in the render window.
Camera AA Samples
As discussed earlier, the Camera (AA) parameter is global multiplier for all other components. The higher the value you specify for this setting, the better the anti-aliasing quality,
and the longer render time will be. In general, use a value of 4 for medium quality, 8 for high
quality, and 16 for ultra high quality.
Note: Motion blur and depth-of-field
The quality of the motion blur and depth-of-field effects can be improved by increasing the
value of the Camera (AA) setting.
In the Render Setup window. In the Arnold Renderer panel > Sampling and Ray Depth
rollout, change Camera (AA), Diffuse, Specular, Transmission, SSS, and Volume Direct
samples to 1 each.
Render the scene. Notice that there is lots of noise in the render because we have only
used 1 ray-per-pixel.
Now, in the Render Setup window, change Camera (AA) to 5. Render the scene. Notice
that we are now able to remove substantial amount of noise from the render because of the
higher number of AA rays [5*5=25 rays-per-pixel].
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Diffuse Samples
This setting controls the number of rays fired when computing the reflected indirect-radiance.
When this value is greater than zero, the
camera rays intersecting with the diffuse
surfaces fire indirect diffuse rays. The
diffuse rays are fired in random directions
within a hemispherical spread. The noise
is introduced when there are insufficient
rays to resolve the range of values from
the environment. You can increase Diffuse
samples value to reduce the indirect diffuse noise and improve quality. Fig. Right
is from Solid Angle which shows how
diffuse rays are propagated in the Arnold render.
Diffuse Samples = 0
Diffuse Samples = 1
Diffuse Samples = 3
Open the Render Setup window. In the Arnold Renderer panel > Sampling and Ray Depth
rollout, change Diffuse > Samples to 5 and then render the scene
** Remember that the Diffuse sampling is done for each Camera (AA) sample, so high values for both Camera (AA) samples and Diffuse samples will tend to result in slow renders.
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Specular Samples
Controls the number of rays fired when computing the reflected indirect-radiance integrated
over the hemisphere weighted by a specular BRDF. The exact number of rays is the square
of this value. Increase this number to reduce the indirect specular noise (soft/blurry reflections). Remember that the specular sampling is done for each Camera (AA) sample, so
high values for both Camera (AA) samples and Specular samples will tend to result in slow
renders.
In the example below the mirrored
surface has a high specular and
roughness values. In the image
on the left, you can see that there
are not enough Specular samples
and therefore there is noise in the
mirror. Increasing the Specular
samples gives a better result.
Specular Samples = 1
Specular Samples = 4
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Transmission Samples
Controls the number of samples used to simulate the microfacet-based transmission evaluations. Increase this value to resolve any noise in the transmission.
If you switch this parameter to zero, the GI_transmission_depth to zero and the noise disappears, you will know that the noise is due to transmission.
Transmission Samples = 2
Transmission Samples = 4
Transmission Samples = 6
SSS
This value controls the number of lighting samples (direct and indirect) that will be taken to
estimate lighting within a radius of the point being shaded to compute sub-surface scattering. Higher values produce a cleaner solution but will take longer to render.
Volume Indirect
Controls the number of sample rays that get fired to compute indirect lighting of the volume.
Ray Depth
The Ray Depth settings corresponding to the Diffuse, Specular, Transmission, and Volume Indirect samples allow you to configure settings that limit the ray recursion based on
ray type. Higher the value you specify, longer the render time will be.
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Arnold Lighting
To achieve professional-quality, realistic renders in 3ds Max, you need to master the art of
lighting. Lights play an important role in the visual process. They shape the world we see.
The trick to simulate realistic looking light effects is to observe the world around us. The
lights you create in a scene, illuminate other objects in the scene. The material applied to
the objects simulates color and texture.
To access Arnold lights, in the Create panel, click Lights,
and then select Arnold from the drop-down list available
below Lights [see Fig. Below].
Now, click Arnold Light in the Object Type rollout; the
Name and Color, General, Shape, Color/Intensity,
Rendering, Shadow, Contribution, and AOV rollouts
will be displayed.
Now, click-drag in a viewport to create a light
in the scene.
Caution: Exposure Control The Physical
Scale value in the Environment and Effects window > Exposure Control influences the rendering with Arnold lights.
In order to get the correct intensity, you
need to disable or adjust the Physical
Scale value to get the expected intensity
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Common Light parameters
As well as honoring the standard 3ds Max light parameters, the Modify Panel will also show
the following Arnold parameters:
Intensity
Intensity controls the brightness of light emitted by the
light source by multiplying the
color.
Exposure (f-stop)
Exposure is an f-stop value
which multiplies the intensity by 2 to the power of the
f-stop. Increasing the exposure by 1 results in double
the amount of light.
In Arnold, the total intensity of
the light is computed with the
following formula:
color * intensity * 2exposure
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Normalize Energy
If enabled, you will be able to tweak the shadow softness by changing the size (i.e., radius)
of the light, without affecting the amount of emitted light. This is very handy for artistic control. Otherwise, if not enabled, the amount of emitted light is proportional to the light’s surface area.
Enabled (default). Radius 2.5.
Disabled. Radius 2.5.
Samples
Controls the quality of the noise in the soft shadows and direct specular highlight. The higher the number of samples, the lower the noise, and the longer it takes to render. The exact
number of shadow rays sent to the light is the square of this value multiplied by the AA
samples.
1 light sample (default)
4 light samples
Specular roughness from top to bottom: 0, 0.1, 0.2, 0.3
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Volume Samples
The volume samples parameter handles the number of samples used to integrate the
in-scattering from direct light. Like the “samples” parameter for surfaces, it is also a squared
number.
Shape Type
The shape of the light. Choose from Point, Distant, Spot, Quad,
Disc, Cylinder Light, Skydome, Photometric and Mesh.
Light Shape Visible
When enabled, the shape of the light is visible in the render as
a self-illuminated object.
Shadow
•
Cast Shadows - Enables the computation of shadows cast from the light.
•
Atmospheric Shadows - Determines if volumetric shadows will be computed. This option is not in Distant or Skydome Lights.
•
Shadow Color - Sets the intensity of each color channel for shadows. Normally this
would be black.
•
Shadow Density - Sets the shadow density, or strength. This controls how the shadow blends with the material on which the shadow is cast: a value of 1.0 produces an
opaque, black shadow, and a value of 0.0 gives no shadow. Normally this would be 1.0.
Contribution
•
Diffuse, Specular, SSS
Per-light scaling for Diffuse, Specular, SSS, and Volume. Weights scaling the light contribution to each of those components independently. Should be left at 1 to produce physically accurate results.
Indirect
The relative energy loss (or gain) at each bounce. This should be left at its default value
of 1.0 for physically meaningful results. Values bigger than 1 make it impossible for GI
algorithms to converge to a stable solution.
Max bounces
The maximum number of times the energy from this light will be allowed to bounce in the
scene.
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Photometric Lights
There are some limitations when using the 3ds Max’s Photometric lights with Arnold. Here’s
is the quick rundown of the features not supported by Arnold:
•
Some of the light shapes do not support the Spherical distribution.
•
Only raytraced shadows are supported, rest of the settings are ignored by Arnold.
•
The Exclude/Include feature is not supported.
•
Incandescent lamp-color shift is not supported. The light shape is not visible to the camera rays.
•
Shadow parameters are not supported.
•
The legacy Atmosphere and Effects are not supported.
Photometric lights simulate real lighting by using physically based energy values and color
temperatures. Many of the parameters for photometric lights are the same as or very similar
to the standard lights we created last week. Here you see the parameters that are specific
to photometric lights. To learn about photometric lights, follow these steps.
1. To create a light, one method is to go to the main menu bar and choose Create / Lights /
Photometric Lights / Target Light to create a photometric target light.
2. When you click on the Target Light, you will get a pop-up, Photometric Light Creation,
recommending that you use the Photographic Exposure Control. Click Yes.
3. In the Left viewport, click to create the light, and then drag from the ceiling down to the
floor. Make sure you stay within the room. You will need to move the light into the room.
Both the light source and target need to be selected. The easiest way to select both the
light and the target is to select the blue string that runs between the two objects.
4. Switch to the Top viewport, and with the Move tool move the light and its target so they
are above the coffee table.
5. Change the viewport rendering type to Realistic in the camera viewport.
6. Select the light source and go to the Modify panel.
7. Template rollout gives you access to several light type presets to save you time in creating a light.
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8. The first rollout under the modifier stack is Templates. Then in the Select A Template
drop-down menu, select Recessed 75W Wallwash (Web). When you add a template to
a photometric light a new rollout appears.
9. Figure shows a photometric light rollout with a “web” distribution essentially defining the
light’s behavior and the light it casts. Lighting manufacturers provide web files that model
the kinds of lights they make, so using these distribution patterns as templates will give
you a lot of options in simulating real-world lights, such as this 75-watt recessed lamp.
10. The Distribution (Photometric Web) rollout You need to take care of some basic stuff
now, so with the light still selected, open the General Parameters rollout and check the
Targeted box. Checking this box turns the target back on for the light. You originally created a targeted light, but when you used the template, it took away the target. Having a
target on a light makes it easier to edit the light’s position.
11. Click the Shadows On box to turn it on. From the drop-down menu, choose Ray Traced
Shadows. Choose Rendering / Exposure Control, and click the Render Preview button in the Exposure Control rollout.
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Physical Camera Exposure Control rollouts in the
Environment and Effects dialog box The preview
may show as either very bright or very dark at
first. If so, the preview function will work perfectly
once you render a frame for the first time.
1. Under the Physical Exposure Control rollout, select Exposure Value (EV) if it isn’t already selected. Set some different values for the EV and see what happens in the Render Preview window.
2. The higher the EV number, the darker the scene will be; when you change the exposure
value, the Render Preview window updates. Set the EV to 6 and render the Room Window Camera.
3. You can continue to work with the EV to experiment with the luminance level. When
you’ve finished experimenting, set the EV around 10 and close the Environment and
Effects dialog box.
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1. Exposure controls adjust output levels and the range of colors of a rendering. These
controls are similar to real-world film exposure settings on a physical camera.
2. With the 75W light still selected, go to the Modify panel, and in the Color group in the
Intensity/ Color/ Attenuation rollout, click the radio button next to Kelvin and change
the value to 5600. This will give the light a bit more warmth by adding more yellow/ red.
3. In the Dimming group, uncheck the box next to the 100% spinner under Resulting Intensity to enable the Intensity parameter.
4. In the Intensity group, select cd and set the cd amount to 200. This will brighten things
up a bit. Figure below: Intensity/ Color/ Attenuation rollout showing the changed parameters Render the scene.
Photometric Light Parameters
Now let’s look in the command panel at the photometric
light’s Intensity/ Color/ Attenuation rollout for the 75W light.
The Color group of parameters controls the color temperature of the light, which you can set either with a color value
or in Kelvin units, just as with real-world photographic lights.
In the drop-down menu, there are different color/ temp settings. The default is D65 Illuminant (Reference White).
The Intensity group of parameters controls the strength or
brightness of the lights measured in lm, cd, or lx.
lm (lumen) This value is the overall output power of the
light. A 100-watt general purpose light bulb measures about
1750 lm.
cd (candela) This value shows the maximum luminous intensity of the light. A 100-watt general-purpose light bulb measures about 139 cd.
lx at (lux) This value shows the amount of luminance created by the light shining on a surface at a certain distance.
The parameters in the Dimming section are also used to control the intensity of the light.
When the Resulting Intensity box is checked, the value specifies a multiplier that dims the
existing intensity of the light and takes over control of the intensity.
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