Rendering with mental ray and 3ds Max open a scene of an attic where the sole source of light is the sun pouring through a skylight. The attic is a bit dark and, because you can't change the intensity of the sun logically, the multiplier value on the Sky Portal is increased by a factor of 10 to brighten the rendered image. Also, the Sky Portal uses the Scene Environment to calculate the color of the light depending on the time of day. However, this creates a problem that is difficult to troubleshoot, so you will learn to fix it in the next exercise. 3.4.2.1 Exercise:SkyPortalartifacts 1. Open the file called Ch03_sky_portal_arti- fact_01.max from the CD-ROM and save it to your hard drive with the name Ch03_ sky_portal_artifact_02.max. Make sure the Camera01 viewport is active and render the scene. The Sky Portal channels the day- light into the attic, but the multiplier value and the Scene Environment option results in bright specks when direct light strikes a surface (see Figure 3.20). 2. Select the Sky Portal in the Camera01 Figure 3.20 ASkyPortalcreatesartifactsontheatticfloor. viewport, and in the Modify panel, you'll see that the multiplier has been set to 10 and the Scene Environment is used to color the light (see Figure 3.21). These are both important settings to achieve the quality of the light that you want in the attic. The problem is that the sampling from the environ- mental sky contains very bright pixels of the sun's disc, and they show up as samples in the area of direct light. 3. One way to fix this problem of artifacts while retaining the quality of light is to disable the sun's disc in the environmental sky. The sun's disc is part of the mr Physical Sky environmental shader. Open the Material Editor and highlight the first sample window in the top row. The mr Physical Sky shader has been cloned here as an instance in order to make adjustments. In the Sun Disk Appearance area of the mr Physical Sky Parameters rollout, enter 0.0 in the Disk Intensity numeric field (see Figure 3.22). This effec- tively disables the sun's disc in the sky. Render the scene. You will see that the artifacts are gone from the floor, but the rendered scene still looks the same otherwise. 4. Close all windows and dialogs and save the file. In this situation, you can eat your cake and have it too: you retain the intensity and the color quality of the light while eliminating the artifacts from the extremely bright pixels of the sun's disc that is visible in the sky, though not to the viewer. 3.5 DaylightsystemandPhysicalSkyshader You've already placed a Daylight system in a scene, but let's take the time to look more closely at how that daylight acts with the physical environment in 64 Figure 3.21 Artifactsarecaused by the multiplier in the scene environmentintheSkyPortal.