Adding Daylight Illumination

Rendering with mental ray: Sky Portal and Exposure Control

Time-of-Day Illumination

 

Autodesk 3ds Max Tutorials > Lighting and Rendering >  Rendering with mental ray: Sky Portal and Exposure Control > 

Using Sky Portal and Photographic Exposure Control

You will now use a Sky Portal to gather existing sky lighting and direct its flow to the interior of the scene.

Add the Sky Portal:

1. On the Create panel, click Lights, and choose Photometric from the drop-down list.

   

2. On the Object Type rollout, click mr Sky Portal, and then turn on Autogrid.

   

3. Right-click the Front viewport label, choose Smooth + Highlights, and then maximize the viewport by pressing Alt+W.
4. Create the Sky Portal by dragging diagonally from the upper-left corner of the window to the lower-right corner, until the entire window is encompassed by the box.

   The Sky Portal should not be much larger than the window.

5. Right-click to complete creating the Sky Portal, then press Alt+W to view all four viewports again.
6. With the Sky Portal object still selected, go to the Modify panel. In the mr Skylight Portal Parameters rollout > Shadows group, make sure Shadows is on and set Shadow Samples to 32.

   

   Increasing the Shadow Samples value improves shadow accuracy, but also increases rendering time.

7. With the Perspective viewport active, press Alt + W again.

   The scene shows that the Sky Portal arrow, which indicates the direction of light flow, is pointing the wrong way: from the interior of the scene outward.

   

8. At the bottom of the mrSkylight Portal Parameters rollout, turn on Flip Light Flux Direction to reverse the light flow.
9. Press Alt+W to view all four viewports, then activate the Camera01 viewport and press F9 to render the scene.

   

   The result is much improved. The Sky Portal has focused the light source, so that more photons are available to be scattered across the room. Nonetheless, the rendered scene is still grainy, and the colors are too bright. We’ll further refine scene illumination by adjusting the scene exposure.

Set exposure:

Proper exposure can improve mid-tones and shadows, and produce more realistic colors.

1. On the Rendering menu, choose Environment to open the Environment and Effects dialog.
2. From the Exposure Control rollout list box, choose mr Photographic Exposure Control.

   

3. On the mr Photographic Exposure Control rollout > Exposure group > Preset drop-down list, choose Physically Based Lighting, Indoor Daylight, then close the dialog.

   

4. Click on Exposure Value (EV) and change the value of 10.0 to 9.0.

5. Lower values add more light to the scene.

   

6. Press F9 to render the scene.

   

   mental ray re-renders the lounge using an exposure preset suitable for indoor illumination. As a result, colors are more muted and subtle, and shadows appear more life-like.

Add an Arch & Design material:

Despite all that you’ve done to this point, the scene still looks a little dull. In this part of the lesson, you’ll take advantage of the mental ray Arch & Design material to add more interesting lighting effects. You’ll switch the original wall panel material on the wall behind the bar with that of frosted glass, then optimize its reflective attributes.

1. Select any wall panel behind the bar, in any viewport.
2. On the toolbar, click Material Editor to open the Material Editor.

   

3. The material currently applied to the wall panel is indicated by a white triangle at each corner of its sample slot. If this isn’t already active, click it to activate it.

4. Click the button labeled Standard to display the Material/Map Browser.
5. Choose Arch & Design (mi) from the list, then click OK.

   

6. On the Material Editor Templates rollout, choose Frosted Glass (Physical).

   

   The glass properties are displayed in the Main Material Parameters rollout. Here, you will customize the glass material by adjusting its light diffusion, refraction, and reflection attributes.

7. On the Main Material Parameters rollout > Diffuse group, click the Color swatch to open the Color Selector. Use the controls to choose an orange color, then click OK.

   

8. Drag the orange color swatch from the Diffuse group to the color swatch in the Reflection group. A Copy Or Swap Colors dialog appears: click Copy.

   

   The light diffusion and reflection properties of the wall panel material now simulate a construction of pigmented glass.

9. Right-click the Refraction group > Transparency spinner arrows to set refractive values at 0.0.

   

   At zero, light will bounce off the material surface rather than penetrate it. This results in more sharply-defined reflected images in the glass.

10. Scroll down to the BRDF rollout.

    BRDF, which stands for bidirectional reflectance distribution function, is a property that lets the material’s reflectivity be determined by the angle from which the object surface is viewed.

11. Turn on Custom Reflectivity Function and in the 0 deg refl. field, specify a value of 0.5.

    

    Viewing material reflections using the By IOR setting is fine if you are viewing reflective surfaces straight on. The Custom Reflectivity Function option is a better choice, however, since it better calculates reflectance from the 45-degree position of the camera.

12. Press F9 to render the scene.

    

    The newly-applied wall panel material has added considerable interest to the scene.