Tuning Light Sources for Rendering


This task gives you some tips to help you tuning the light source parameters when rendering a scene.

Open the TuningLightsStart.CATProduct document.

Click Shading with Material in the View toolbar then select View > Render Style > Perspective.

  1. Click Quick Render .

    Step 1 - No light source
    In our example, we are going to create a light source that matches the lighting of the environment pictures, i.e. the sun light.
  2. Click Directional Light then click Quick Render again to check the result.

    Step 2 - One directional light source

    As you can see above, the result is better but still not realistic enough.

    Note: if there is not shadow cast on the pavement, edit the Bottom wall properties then select the On check box in the Lighting tab.

  3. Modify the light orientation using the green manipulators so that the red car shadow matches the shadows of the cars parked behind. For our example, a correct position would be:

    • origin in top rear left

    • target in bottom front right

    Changing the viewpoint may be helpful to position the light (for example you can use the Top or Left view).

  4. Double-click the camera to go back to the original viewpoint then click Quick Render .

    When using spot or point lights, pay attention to the lighting end in order to make sure that the light cone includes the object and thus, correctly illuminates it. Otherwise, the object will be too dark.

    For more information on light sources, refer to Defining a Light Source in this guide.

  5. For a more realistic lighting, you may need to create soften shadows. To do so, simply duplicate the original light (Copy > Paste), slightly modify the orientation of the new lights then decrease the intensity (only one light cast shadows) as shown in step 6:

  6. Access the Lighting tab in the Properties dialog box to soften the light and give it a faint yellow color.

    Intensity parameters: Red= 173, Green= 173, Blue= 167

    Do not forget to select the Ray Traced check box to activate shadows.

  7. Edit the Lighting parameters of the duplicated light (intensity parameters: R=G=B= 80) then select the Enable check box in the Shadows tab before creating a quick render.

    You can click Stop to interrupt the process as soon as an unsatisfactory result is detected.

    When using a spot or point light, changing the attenuation may also make the lighting more realistic.

  8. When satisfied, click Create a Shooting then render this shooting to check the result:

    Shooting rendered from current viewpoint
    Shooting rendered from camera viewpoint
    Bear in mind that the more light sources, the more difficult the tuning of the scene's global illumination.

For more information on the shooting creation, refer to Setting Image Quality Parameters in this guide.