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Rendering menu > Advanced Lighting > Advanced Lighting dialog > Select Advanced Lighting rollout > Choose Radiosity.
Radiosity is a technique to calculate indirect light. Specifically, radiosity calculates the interreflections of diffuse light among all the surfaces in your scene. To make this calculation, radiosity takes into account the lighting you’ve set up, the materials you’ve applied, and environment settings you’ve made.
The radiosity processing of a scene is distinct from the rendering process. You can render without radiosity. However, to render with radiosity, you must always calculate radiosity first.
Once a radiosity solution for a scene has been calculated, it can be used in multiple renderings, including multiple frames of an animation. If there are moving objects in the scene, radiosity might need to be recalculated; see the section “Object Animation,” below.
For an overview of radiosity and how radiosity works in 3ds max, see Radiosity Solution.
For radiosity workflow suggestions, see Radiosity Workflows.
Note: Radiosity is also known as global illumination.
For imported geometry, you must make sure that units are consistent in your scene before processing radiosity (for example, a wall is 8 feet high, not 8 kilometers high). Units in 3ds max must match the units of the model because the radiosity engine always uses an inverse square falloff for lights. Therefore, distance is crucial.
To make sure your units are setup correctly, use the Units Setup dialog. The Scene Unit is the most important unit in this dialog. This is the unit that 3ds max uses for its calculations. The Display Unit is just a tool that lets you customize how units are displayed in the user interface.
The following two scenarios show how to set unit scales after importing geometry that has been created using different units than what is currently set in 3ds max:
Example 1: You import a table that was created in AutoCAD using metric scale. The table is 9 units long, which corresponds to an actual length of 90 centimeters. When the table is imported into 3ds max, it will measure 9 scene units. Therefore, in the Units Setup dialog, you must set Scene Unit Scale to 1 Unit=10 centimeters. Your table is now the correct units because it is 90 centimeters long in 3ds max model.
Example 2: You have an AutoCAD model that was created using Architectural Units. The model is a room measuring 20’-4” long. In AutoCAD, Architectural Units are stored as inches. Therefore, before importing the model to 3ds max, make sure to set the Scene Unit Scale to 1 Unit=1 inch. Once imported to 3ds max, the room will measure 244 units long (20’*12+4”).
This is an overview of how radiosity works in 3ds max:
Object by object, 3ds max loads a copy of the scene into the radiosity engine.
3ds max subdivides each object according to the Global Subdivision Settings in the Radiosity Meshing Parameters rollout.
3ds max emits a certain amount of rays on the average scene reflectance and number of polygons. The brightest light source will have more rays to emit than the weakest light source.
These rays bounce around randomly in the scene and deposit energy on the faces.
3ds max updates the viewports by taking all the energy from the faces and spreading it to the closest vertex.
See the section that follows, “Refinement Steps for Radiosity,” for a more detailed description of the solution process.
The radiosity process involves three stages of increasing refinement. The first two stages occur during the primary radiosity processing, and the third stage can be used during the final rendering.
Within each of the first two stages, you can stop and start the processing at any time. This can be useful for evaluating interim results or increasing the level of accuracy you desire. For example, you can interrupt the Initial Quality stage at 50% and jump ahead to the Refine stage if you wish. However, once you enter the Refine stage, you cannot continue further iterations of Initial Quality unless you restart the solution.
The stages of a radiosity solution are Initial Quality, Refine, and then Regathering.
In the Initial Quality stage, the distribution of diffuse lighting in the scene is calculated by essentially mimicking the behavior of real photons. Rather than tracing the path of an essentially infinite number of photons, statistical methods are used to choose a much smaller set of “photon rays” whose distribution in space is representative of the actual distribution. As with any statistical sampling process, the greater the number of rays used in the approximation, the greater the accuracy of the solution. During the initial quality stage, the overall appearance of the lighting level of the scene is established. The results can be interactively displayed in shaded viewports.
The initial quality stage performs repeated passes, which are shown in the dialog’s progress bar.
Refine Iterations (All Objects) and Refine Iterations (Selected Objects)
Because of the random nature of the sampling during the initial quality stage, some of the smaller surfaces or mesh elements in the scene might miss being hit by enough rays (or any rays at all). These small surfaces remain dark, and result in the appearance of “variance” or dark spots. To alleviate these artifacts, the Refine stage “regathers light” at every surface element.
You can perform the Refine stage for the entire scene, or for selected objects in the scene.
Even after the Refine stage, it is still possible for visual artifacts to appear in a scene because of the topology of the original model. These artifacts sometimes appear as shadow or light “leaks.” To eliminate even these model-based artifacts, a third, optional refinement stage known as Pixel Regathering occurs at the time of image rendering. This involves a final “regather” process for each pixel of the image. Regathering can add a considerable amount of time to the rendering of a final image, but it also produces the most detailed and artifact-free images possible.
One benefit of using Regathering is that it means the initial modeling and mesh resolution don’t need to be nearly as “refined” or “tight” as would otherwise be required.
The radiosity solution is calculated for each frame if any object is animated in the scene (the default is to calculate the current frame only). You specify the parameters (goals/quality) you want to reach in the Advanced Lighting dialog. It is recommended to run a solution first and verify if it’s successful before proceeding to the whole animation. These parameters will then be reprocessed for each frame.
You go to the render dialog, Common Parameters rollout, and enable the option Compute Advanced Lighting When Required, and then render the scene. The radiosity is processed for the first frame and then rendered. 3ds max then moves to the next frame, processes radiosity, renders, and so on.
If objects remain static in the scene and only the camera moves, you can solve radiosity at frame 0, and when you render the animation, turn off Compute Advanced Lighting When Required.
Example: To process radiosity with photometric lighting:
Use a scene that has geometry set to the correct scale.
For example, if the ceiling is 96 scene units high in the model, make sure the units are set to US Standard (inches) and not Metric.
On the Create panel, click Lights.
Choose Photometric from the drop-down list. (The default is Standard.)
In the Object Type rollout, click Target Point.
Drag in a viewport. The initial point of the drag is the location of the light, and the point where you release the mouse is the location of the target.
The light is now part of the scene.
Set the creation parameters.
You can use the Move transform to adjust the location of the light or its target.
Click Render Scene to preview the lighting.
Make any changes you need to adjust the rendering.
Choose Rendering > Environment to display the Environment dialog.
On the Exposure Control rollout of the Environment dialog, choose Logarithmic Exposure Control from the drop-down list.
On the Logarithmic Exposure Control rollout, adjust the parameters until the scene lighting is acceptable.
For example, a brightness of 65 and a contrast of 50 are good values for interior scenes.
Choose Rendering > Advanced Lighting. On the Advanced Lighting dialog, choose Radiosity as the advanced lighting type.
The rollouts for radiosity are displayed.
On the Radiosity Parameters rollout, click Start to process radiosity.
Click Render Scene to render the scene after radiosity processing completes.
Example: To process radiosity with standard lighting:
Photometric lights are recommended for use with radiosity. But if you are working on a scene that already contains standard lights, you can follow these guidelines.
Create or load a scene containing the appropriate geometry for lighting. There is no need to adjust any scale factors.
On the Create panel, click Lights.
Standard is the default choice of light type.
In the Object Type rollout, click a light type such as Target Spot.
Drag in a viewport. The initial point of the drag is the location of the spotlight, and the point where you release the mouse is the location of the target.
The light is now part of the scene.
Set the creation parameters for the light.
Click Render Scene to preview the lighting.
Make any changes you need to adjust the rendering.
Choose Rendering > Advanced Lighting. In the Advanced Lighting dialog, choose Radiosity as the advanced lighting type.
The rollouts for radiosity are displayed.
On the Radiosity Processing rollout, under Interactive Tools, click Setup to display the Environment dialog where you set exposure controls.
Note: The exposure controls allow you to control only the intensity of the indirect lighting. 3ds max retains the original intensity and effect for the direct lighting.
On the Exposure Control rollout of the Environment dialog, choose Logarithmic Exposure Control from the drop-down list.
On the Logarithmic Exposure Control rollout, turn on Affect Indirect Only.
On the same rollout, use the Physical Scale setting to assign the standard light a photometric value in candelas.
Click Render Scene to render the scene after radiosity processing.
Radiosity controls appear as rollouts on the Advanced Lighting dialog.
Controls the processing of radiosity.
Reset All—When you click Start, a copy of the 3ds max scene is loaded into the radiosity engine. Clicking Reset All clears all the geometry from the engine.
Reset—Clears the light levels from the radiosity engine, but doesn’t clear the geometry.
Start—Starts the radiosity processing.
Stop—Stops the radiosity processing.
Keyboard shortcut: ESC
The options in this group set the behavior of the first two stages of the radiosity solution, Initial Quality and Refine.
Initial Quality—Sets the quality percentage at which to stop the Initial Quality stage, up to 100%. For example, if you specify 80%, you will get a radiosity solution that is 80% accurate in energy distribution. A goal of 80 to 85% is usually sufficient for good results.
During the Initial Quality stage, the radiosity engine bounces rays around the scene and distributes energy on surfaces. Between each iteration, the engine measures the amount of variance (noise between surfaces) that was computed.
Most of the brightness of the scene is distributed in the early iterations. The contribution to the scene’s average brightness decreases logarithmically between iterations. After the first few iterations, the brightness of the scene does not increase much, but subsequent iterations reduce the variance in the scene.
Note: The “quality” refers to the accuracy of energy distribution, not to the visual quality of the solution. Even at a high Initial Quality percentage, the scene can still show considerable variance. This variance is resolved by the subsequent stages of the solution.
Increasing the percentage value of Initial Quality.
Increasing quality does not greatly increase the average brightness of the scene, but it decreases the variance between different surfaces in the scene, such as the faces of the sphere.
Refine Iterations (All Objects)—Sets the number of Refine iterations to perform for the scene as a whole. The Refine Iterations stage increases the quality of the radiosity processing on all objects in the scene. Gathers energy from each face in order to reduce the variance between faces using a different process from the Initial Quality stage. This stage does not increase the brightness of the scene, but it improves the visual quality of the solution and significantly reduces variance between surfaces. If you don’t reach an acceptable result after processing a certain number of Refine iterations, you can increase the number and continue processing.
Tip: If you plan to use Regathering at render time, you generally don’t need to perform the Refine stage to get good-quality final renderings.
Note: After 3ds max processes Refine Iterations, Initial Quality is disabled and you can’t change it until you click Reset or Reset All.
Large image with no iterations has areas of uneven illumination.
Inset images: After a number of iterations, the uneven areas have been corrected.
Refine Iterations (Selected Objects)—Sets the number of Refine iterations to perform for selected objects, using the same method as Refine Iterations (All Objects). Make an object selection and then set the number of iterations you require. Refining selected objects rather than the entire scene can save a lot of processing time. Typically, this option is useful for objects that have a lot of small surfaces and show a lot of variance, such as railings or chairs or highly subdivided walls.
Note: After 3ds max processes Refine Iterations, Initial Quality is disabled and you can’t change it until you click Reset or Reset All.
Process Refine Iterations Stored in Objects—Each object has a radiosity property called Refine Iterations. Each time you refine an object selection, the number of steps stored with these objects is incremented.
When you reset the radiosity solution and then start it again, the steps for each objects are refined automatically, provided this toggle is turned on. This is useful when you are creating animations, when the radiosity needs to be processed at every frame, and the same level of quality between frames has to be maintained.
The options in this group help you adjust the display of the radiosity solution in the viewport and in the rendered output. These controls take effect immediately on an existing radiosity solution and do not require any additional processing for you to see their effects.
Filtering—Reduces the amount of noise between surface elements, by averaging the lighting levels with the surrounding elements. A value of 3 or 4 is usually sufficient. If you use too high a value, you risk losing detail in the scene. However, since Filtering is interactive, you can readily evaluate the result and adjust it as you need.
For a 65% quality solution, increasing the filter from 0 to 3 creates a much smoother diffuse light. The results are comparable to a much higher quality solution.
Exposure Control—Displays the name of the current exposure control.
(When you change the exposure control by accessing Environment from the Rendering menu, the name display in the Radiosity dialog updates automatically.)
Setup—Displays the Environment dialog, where you access the Exposure Control rollout; there, you can choose the current control and the parameters rollout for a particular exposure control.
Display Radiosity in Viewport—Toggles the display in the viewports between radiosity and standard 3ds max shading. You might want to do this to increase display performance.
In order to create the lighting of a scene, 3ds max calculates the intensity for discrete points in the environment by subdividing the original surfaces into elements which are part of a radiosity mesh. This rollout allows you to determine whether you want a mesh or not, and to specify the size of the mesh elements in world units. For quick tests, you might want to turn off the mesh globally. The scene will look flat, but the solution will still give you a quick impression of the overall brightness.
The finer the mesh resolution is, the more accurate the lighting detail will be. But there is a trade-off in time and memory.
Meshing (shown in light red) subdivides flat surfaces in the scene.
Left: No mesh. The solution looks very flat.
Middle: Coarse mesh, every 24 inches. The lighting improves.
Right: Fine mesh, every 4 inches. The lighting reveals more subtle effects.
Note: A tight meshing is not necessary when you use the regathering feature in the Rendering Parameters rollout.
Controls the creation of a radiosity mesh and its size in world units.
Note: You can override the settings in this group from the Advanced Lighting panel of the Object Properties dialog. This allows you to have a different mesh resolution on some objects. For example, you might want to have a finer mesh on an important wall surface that you know will have a lot of detail. To display the Object Properties dialog, right-click a selected object and choose Properties from the quad menu.
Enabled—Turns on the radiosity mesh for the entire scene. Turn off the mesh when you want to perform quick tests.
Meshing Size—Sets the size of the radiosity mesh elements in world units.
Left: A simple box with no subdivision.
Middle: The box faces are subdivided.
Right: The box faces are subdivided with a smaller Meshing Size.
The light painting tools in this rollout allow you to touch up shadowed and illuminated areas manually. You can use these tools to touch up shadow and light-leak artifacts without having to do additional remodeling or radiosity processing. Using Pick Illumination, Add Illumination, and Remove Illumination, you can add or remove illumination on one selection set at a time.
To use the light painting tools, you must first select objects. The cursor changes to the light painting tool you select: Pick Illumination, Add Illumination, or Remove Illumination. The button in the rollout turns orange to indicate you’re in the appropriate mode.
You can pick, add, or remove illumination through objects. For example, if you select the floor as an object, you can work under the bookshelf, by working through it. Once in light painting mode, you can’t select another object unless you cancel the operation.
Add Illumination—Adds illumination starting at the vertex of a selected object. 3ds max adds illumination based on the amount in the Pressure spinner. The pressure amount corresponds to a percentage of the sampled energy. For example, if a wall has about 2,000 lux on it, Add Illumination adds 200 lux to the surface of the selected object.
Remove Illumination—Removes illumination starting at the vertex of a selected object. 3ds max removes illumination based on the amount in the Pressure spinner. The pressure amount corresponds to a percentage of the sampled energy. For example, if a wall has about 2,000 lux on it, Remove Illumination removes 200 lux from the surface of the selected object.
Pick Illumination—Samples the amount of illumination from a surface that you select. To save you from inadvertently making bright or dark spots, Pick Illumination uses an amount of illumination relative to the surface illumination you sample. Click the button, and move the eyedropper cursor over the surface. When you click a surface, the amount of illumination in lux or candelas is reflected in the Intensity spinner. For example, if you used Pick Illumination over a wall that has 6 lux of energy, then 0.6 lux displays in the Intensity spinner. The amount of illumination 3ds max adds or removes on the surface will be this value multiplied by the Pressure value.
Clear—Clears all the changes you made. Processing additional radiosity iterations or changing the filtering amount will also discard any changes to the solution you made with the light painting tool.
Intensity—Specifies the intensity of the illumination in lux or candelas depending on the units you have selected in the Customize > Units Setup dialog.
Pressure—Specifies the percentage of the sampled energy to be used when you add or remove illumination.
Using light painting to add or remove light in a radiosity solution.
Provides parameters that allow you to control how you want to render the radiosity-processed scene.
By default when you render, 3ds max first recalculates the shadows from light objects, then it adds the result of the radiosity mesh as ambient light.
3ds max offers three possible rendering options in this rollout:
Re-use Direct Illumination from Radiosity Solution—A quick render that calculates shadows from the radiosity mesh, so they tend to be a bit coarse.
Render Direct Illumination—A longer render that calculates shadows by the standard renderer, so they are a better quality.
Regather Indirect Illumination—The longest and best render that calculates shadows from all the light sources and corrects artifacts and shadow leaks.
Note: This is extremely intensive for your CPU and uses a lot of RAM, so it might not be practical for print-resolution images (for example, 4000 x 4000 pixels).
Re-use Direct Illumination from Radiosity Solution—3ds max doesn’t render direct lights, but uses the direct lighting stored in the radiosity solution. If you turn on this option, the Regather Indirect Illumination option is disabled. The quality of shadows in the scene depends on the mesh resolution. Capturing fine shadow details might require a fine mesh, but in some situations this option can speed up overall rendering time, especially for animations, because the lights don’t have to be recalculated by the scanline renderer.
Left: Direct light only is stored in the radiosity mesh.
Middle: Indirect light only is stored in the radiosity mesh.
Right: Direct and indirect light both stored in the radiosity mesh (the shadows are usually very coarse).
Render Direct Illumination—3ds max renders shadows from the lights at each rendering frame, and then adds indirect light from the radiosity solution. This is the default rendering mode.
Left: Direct light calculated only by the scanline renderer.
Middle: Indirect light calculated only by the radiosity mesh.
Right: Direct and indirect light combined.
Regather Indirect Illumination—In addition to recalculating all the direct lighting, 3ds max recalculates the indirect lighting at each pixel by regathering illumination data from the existing radiosity solution. Using this option can produce the most accurate, artifact-free images, but it can add a considerable amount of rendering time.
Note: If you know that you want to use the regathering option, then typically you don’t need as dense a mesh for the radiosity solution. Even if you don’t subdivide the surfaces at all and do an Initial Quality of 0%, the regathering will work, and might provide an acceptable visual result (useful for quick tests as well). However, accuracy and subtle details depend on the quality of the radiosity solution stored in the mesh. The radiosity mesh is the foundation for the regathering process.
In the following illustrations, solutions were processed with an Initial Quality of 0%. There is a high variance between small surfaces when a dense mesh is used. Regathering gives acceptable results regardless of mesh density. But more subtle details appear with a denser mesh; for example, at the base of the sculpture.
No mesh
Left: Model subdivision
Middle: Viewport result
Right: Result of regathering
Coarse mesh
Left: Model subdivision
Middle: Viewport result
Right: Result of regathering
Fine mesh
Left: Model subdivision
Middle: Viewport result
Right: Result of regathering
Rays per Sample—The number of rays 3ds max casts for each sample. 3ds max casts these rays randomly in all directions to calculate (“regather”) the indirect illumination from the scene. The more rays per sample, the more precise the sample will be. Fewer rays per sample produce more variance, creating a more grainy effect. Processing speed and precision are affected by this value. Default=64.
Filter Radius (pixels)—Averages each sample with its neighbors in order to reduce the noisy effect. Default=2.5 pixels.
Note: Pixel radius varies according to the output resolution. For example, a 2.5 radius is OK for NTSC resolution, but it might be very large for smaller images, or too precise for very large images.
Pixel radius of 2
Left: 10 rays per sample
Middle: 50 rays per sample
Right: 150 rays per sample
Pixel radius of 5
Left: 10 rays per sample
Middle: 50 rays per sample
Right: 150 rays per sample
Pixel radius of 10
Left: 10 rays per sample
Middle: 50 rays per sample
Right: 150 rays per sample
Increasing the number of rays per sample can greatly increase rendering time. The images on the right can take nearly six times as long to render as the images on the left. Increasing the filter radius also increases render time, but not as dramatically.
Clamp Values (cd/m^2)—This control is expressed as a luminance value. Luminance (candelas per meter squared) represents how brightly you perceive a material. Clamp Value sets an upper limit on the luminance that will be considered in the Regathering stage. Use it to avoid the appearance of bright spots.
Bright polygons in the scene can create a “sparkle” effect of bright spots.
These bright spots are artifacts not of the number of samples cast, but rather of the presence of bright polygons in your scene. During the Initial Quality stage, this bright energy gets bounced in random directions, leading to a “sparkle” effect. Typically you can detect these polygons before regathering.
During the final Regathering stage, bright spots can be avoided by setting Clamp Values somewhat below the luminance of these bright surfaces and spots.
Bright spots have been reduced by clamping.
Tip: Use Render Region to render just the area of the bright spots to find rapidly the right clamp value to use.
Be careful with this control: Clamp Values let you clamp any intensity, and the rendering might become darker than it should be because you have clamped indirect illumination that is to be expected, thus dimming the effect of the radiosity solution.
These controls can help you speed up rendering time. They reduce the number of light samples taken. The ideal settings for undersampling vary greatly from scene to scene.
Undersampling initially takes samples from a grid superimposed on the pixels of the scene. Where there is enough contrast between samples, it subdivides that region and takes further samples, down to the minimum area specified by Subdivide Down To. Lighting for areas not directly sampled is interpolated.
Tip: If you use adaptive undersampling, try adjusting the Subdivision Contrast value to obtain the best results.
Adaptive Undersampling—When on, the radiosity solution uses undersampling. When off, it does not. Turning off undersampling can increase the detail of the final rendering, but at a cost of rendering time. Default=on.
Initial Sample Spacing—The grid spacing for initial samples of the image. This is measured in pixels. Default=16x16.
Subdivision Contrast—The contrast threshold that determines when a region should be further subdivided. Increasing this value causes less subdividing to occur. Reducing this value can cause unnecessary subdivide. Default=5.0.
Subdivide Down To—The minimum spacing for a subdivision. Increasing this value can improve render time at a cost of accuracy. Default=2x2.
Depending on the scene geometry, grids larger than 1x1 might still be subdivided below this specified threshold.
Show Samples—When on, sample locations render as red dots. This shows where the most sampling has taken place, which can help you choose the optimal settings for undersampling. Default=off.
Lists the current level of quality and number of refine iterations in the radiosity process.
Solution Quality—The current level of quality in the radiosity process.
Refine Iterations—The number of refine iterations in the radiosity process.
Elapsed Time—The time spent processing the solution since the last reset.
Lists information on the radiosity processing of the scene.
Geometric Objects—Lists the number of objects processed.
Light Object—Lists the number of light objects processed.
Note: Self-illuminated objects count as one light per face.
Radiosity Mesh—Lists the size of radiosity mesh elements in world units.
Note: Transparent, 2–sided, and translucent objects' faces are counted twice.
Mesh Elements—Lists the number of elements in the mesh processed.
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