Lighting Tutorials > Lighting and Rendering the Villa in Daylight >
Using Sky Portals and Photographic Exposure Control

A Sky Portal is a 3ds Max Design light object that gathers the sky light (as opposed to direct sunlight) generated by the Daylight system. It then directs the light flow through selected objects, such as doors, glass doors, and windows, so the interior of buildings can be illuminated.

Set up the lesson:

- Continue working on your own scene file, or open the scene file med_villa_lighting_skyportals.max.

Render the scene for later comparison:

1. Activate the Camera-Terrace viewport, and render the scene.
2. On the Rendered Frame Window, make a clone of the image.
3. Minimize the two Rendered Frame Windows.

Isolate the windows and doors:

1. On an empty area of the main toolbar, right-click and choose Layers from the pop-up menu.

   3ds Max Design opens the Layers toolbar.

2. Choose Doors & Windows from the drop-down list of layers.
3. Click (Select Objects In Current Layer) to select the doors and windows.
4. Right-click any viewport and on the quad menu, choose Isolate Selection to display only the selected objects.
5. Activate the Camera-Terrace viewport, press P to switch to Perspective view, then navigate with (Pan) and (Field-Of-View) until all the windows are clearly in view.
6. Orbit the view so that the windows and doors face you, as shown in the next illustration.
7. Press Alt + W to maximize the Perspective view, then press F4 to view Edged Faces.
   TipMove the Isolated Selection dialog and the Layers toolbar to a corner of the viewport where they don’t obscure any geometry.

Add the Sky Portals:

1. On the Create panel, click (Lights). On the Object Type rollout, click “mr Sky Portal” to turn it on, then turn on AutoGrid.
2. In the Perspective view, create the first Sky Portal by dragging diagonally from the lower-left corner of any window to the upper-right corner, until the entire opening is covered.
   TipWhen you create a Sky Portal, make sure that the Z axis of the AutoGrid grid is perpendicular to the glass pane of the window or door, as shown in the illustration.
3. Repeat the previous step for every door and window object in the scene, except for the PivotDoor02 object (it is second from the right in the upper-right corner of the viewport).
4. Orbit the Perspective view so that the windows and doors are visible from their sides, as shown in the next illustration.

   The yellow arrow for each SkyPortal object indicates the direction of the light flow, or flux. Because you used AutoGrid to place the SkyPortal object on the exterior face of the doors and windows, the light flux arrows point in the proper direction, into the building. (If you created the Sky Portal from the inside of the building, you would have to reverse the light flux either by rotating the window/door, or turning on Flip Light Flux Direction on the “mr Skylight Portal Parameters” rollout.)

5. Orbit the scene again until the PivotDoor02 object is facing you. Create another Sky Portal object by dragging across this door.
6. Orbit the scene one last time so that the sides of the doors and windows are visible, as shown in the next illustration. The PivotDoor02 object should have its light flux direction pointed in the correct direction: into the room from the opposite side of the building.

Adjust the Sky Portal settings:

1. Select any Sky Portal object you created by clicking its yellow light-flux arrow.
2. Go to the Modify panel.

   Each Sky Portal has an “mr Skylight Portal Parameters” rollout. The Multiplier control on this rollout lets you boost the amount of light transmitted by the Sky Portal. For now however, leave the Multiplier set to 1.0.

   You do not need interior shadows for an exterior shot when viewed from a distance. Also, turning off Shadows helps to reduce render time. If you had created a single Sky Portal, you could turn off the Shadows toggle here; but since you’ve created several Sky Portal objects, it is easier to use the Light Lister.

3. From the main menu choose Tools Light Lister. In the Light Lister dialog Shadows column, turn off Shadows for each mr Sky Portal object in the scene.
4. Close the Light Lister.
5. Click Exit Isolation Mode.

   If 3ds Max Design opens a Select Camera dialog, choose Camera-Terrace and then click OK. Otherwise, click the Perspective viewport POV label and choose Cameras Camera-Terrace.

6. Press F4 to return to regular shading mode.

Render the terrace to see the effect of the Sky Portals:

1. Render the Camera-Terrace viewport and compare the result with the rendered frame you cloned earlier in this lesson.

   The result is subtle, but improved. The window and door openings are slightly lighter because now the Sky Portals are channeling sky light into the villa.

   You can understand the effects of the Sky Portals better by looking at the villa from the inside.

View the sky portal effect from the interior of the villa:

1. Switch the Camera-Terrace viewport to a Camera-Interior view, then render the scene.

   Because scene exposure is set to outdoor conditions, the outside portion of the scene is properly exposed, but the interior is too dark. You need to adjust the exposure setting to compensate for the lower light of the building interior.

2. On the Rendered Frame Window, click (Environment And Effects Dialog (Exposure Controls)) to display the Environment And Effects dialog.
3. On the mr Photographic Exposure Control rollout Exposure group, make sure Photographic Exposure is chosen, then set Shutter Speed to 125.0 (1/125 Sec.).

   Keep the Environment And Effects dialog open for now.

4. Make a clone of the rendered frame, then click Render to render the scene again.

   The slower shutter speed is now permitting more light to enter the camera, resulting in a better inside exposure.

   You can further improve the interior lighting by increasing the number of bounces to each ray of light entering the interior.

5. Clone the current rendered frame. In the Rendered Frame window mental ray controls, change the Final Gather Precision to Low, and increase the value of FG Bounces to 2.
6. Render the interior view again and compare the result with the cloned frame.
7. Close the earlier cloned frames, then make a new clone of the most recent rendering.

   If you wish, you can take things further by dragging the Final Gather Precision and Image Precision slider bars to the right. Keep in mind that the greater the precision, the slower the rendering time.

   For this interior scene, it is appropriate for the door’s Sky Portal to cast shadows. This is because room illumination would ordinarily be affected by shadows cast by the door frame.

8. Select the Sky Portal object by clicking its gizmo in the center of the door. On the “mr Skylight Portal Parameters” rollout, turn Shadows on.
9. Render the scene again.

   If you compare the result with the cloned rendering, you can see that the shadows where the walls meet each other, and where they meet the ceiling, are wider and darker than they were before.

10. For the selected Sky Portal, turn Shadows off again.
11. Change the view back to Camera-Terrace.
12. On the Environment And Effects dialog, set the Shutter Speed back to a proper exposure for the outdoor scene, which is 512 (1/512 Sec.).

Save your work:

- Save the scene as my_villa_skyportals.max.

Next

Time of Day Illumination