Cinema 4D / BodyPaint 3D Program Documentation Tutorials Light and Shadow Tutorial Visualizing Interior Spaces using Global Illumination
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Lighting

Now that our objects have materials assigned to them we will turn our attention to lighting the scene. Since this is a daylight scene and the interior lights must therefore not be turned on, we will use a Physical Sky as a main source of light that casts light through the window into the room. A Floor object has also been added to keep the light from passing below the horizon line.

You can continue working with the scene you just textured or you can open the following scene:


Physical Sky

Almost all outdoor scenes and many indoor scenes require sunlight and a sky. For the latter you can simply use an image but using a Physical Sky object is more practical because the date, season, place and even the weather can be defined. And because this object encloses the entire scene you are able to freely change your angle of view independent of the background. Create a Physical Sky from the Create | Physical Sky menu. As you can see in the image below, this object’s Basic tab already contains numerous options for defining the type of weather or what the sky should look like. The options farther below can be enabled or disabled depending on which elements your sky should contain.

Our scene only requires the Sky option to be enabled in order to create a soft, indirect light. Using the Time and Location tab’s settings you can define when and where the scene should be on the globe. This affects the color and position of the sun. If you render the scene, the result should be similar to the image below, depending on your own time and position.

Surely you’ve noticed that the room has a strong blue tinge. This is a result of the sky’s blue light, e.g., the light that the sky’s sphere itself emits. It casts no shadows and permeates all areas of the room. The image itself is too dark because no indirect lighting is being created.

Global Illumination

As soon as we add Global Illumination (GI) in the Edit Render Settings... menu’s Effects settings, the rendered result will change dramatically. We now have indirect light with shadows but the room is still very dark. We will have to add more light to the scene.

Light maps

First, a Secondary Method should be added from the corresponding GI menu. By default, the renderer only generates a rebound of the light, which is why Secondary Method is set to None by default. Combining two GI methods helps get a good median value for render time and render quality for the final rendering. The best selection for this scene is Light Mapping (LM). This setting can be used for interior and exterior scenes as a supplement to either Irradiance Cache (IR) or Quasi Monte Carlo (QMC). The advantages of using LM are faster rendering, ease of use and the minimal difference in speed compared to higher Maximum Depth values. Your rendered image should look like the one below:

Still dark but much brighter. For now we will ignore the GI artifacting, which is especially obvious in the corners, because we still need to add more light. There are a lot of ways to add more light to the scene. For example, we can increase the Physical Sky’s Intensity value or we can increase the Maximum Depth value (the frequency with which light is reflected), or we can add lights. Unfortunately, none of these methods is particularly effective: Increasing the sky’s Intensity would over expose the area around the window and the rest of the scene will be too dark; a higher Maximum Depth value would increase render time and only create a fraction of the additional light needed; and adding lights is simply not practical. So which possibilities do we have? Fortunately we still have three aces up our sleeve: GI Portals, the Physical Camera and Color Mapping.

GI Portals

Using Portals is one of the most effective ways to add light and simultaneously reduce artifacting. Portals are most effective where light is cast from a smaller region such as a window. In order to use GI Portals, we must first add surfaces for window panes. This polygon object will then be assigned a corresponding material. Creating a material for a GI Portal is very easy: Create a new material and disable all channels except for the Luminance, Transparency and Reflectance (for which you delete the Specular layer). channels. Enable the GI Portal option in the Attribute Manager’s Illumination tab. After assigning the material to the window panes, the rendered image should look similar to the one below:

The scene is now brighter and basically all artifacting is gone, but we still need more light.

Physical Camera

This is an ideal situation for using the Physical Camera. In the Render Settings menu, set Renderer to Physical. A new Physical sub-menu will appear. We will take a look at these settings later. Go to the Physical Camera object’s Physical tab in the Attribute Manager. This tab contains many settings that are also offered by real cameras. Enable the Exposure option and set F-Stop (f/#) to 5.6, which will let more light in, and set the ISO value to 400. The rendered result is much different than before:

The room now has the desired brightness but another problem has arisen: there’s an over-exposed region near the rear window and we can still see GI artifacts here and there. These artifacts can be removed fairly quickly by setting Interpolation Method to Fixed in the Global Illumination settings’ Light Mapping tab.

Color mapping

Color Mapping will be used to solve the remaining issues. Once it’s added in the Render Settings we only have to modify a few settings. The most important are: Exponential, HSV Model and Dark Multiplier.

Normally, a linear multiplication will result if Color Mapping is disabled (or the Exponential option is disabled). Each pixel will be multiplied based on its brightness and luminous, lively images will result. Very bright color components (in excess of 100%) will be cut out, which leads to over-exposed regions around bright light sources and results in a the linear multiplication mode being unsuited for such interior scenes.

Exponential (enabled by default in Color Mapping) on the other hand produces each pixel’s brightness exponentially. This causes dark regions to render slightly brighter and over-exposed regions to render darker, which means that the overall calculation is less linear and therefore more natural and balanced.

Note that the color’s saturation is also affected per pixel by the multiplication of the brightness. In some cases this can result in colorless or dreary images. The HSV Model option (also enabled by default in Color Mapping) makes sure that color shade and saturation are maintained.

Finally, we will increase the Dark Multiplier value to 3 to generate a little more light in the room. The result is a balanced and appealing image:

Last steps

We can fine-tune the Physical Camera a little, e.g., by adding a Vignetting Intensity of 20% and a very slight Lens Distortion - Quadratic of 0.5% to make the image more photo-realistic.

The Color Correction effect can be used to improve Brightness and Contrast.

For the final rendering, set Physical Camera’s Sampling Quality to Medium and the Blurriness Subdivision (Max) to 4 to reduce graininess in reflections.

This is what the room looks like when the lighting setup is finished:

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