Using IBL

Bryce 6 introduces Image Based Lighting (IBL) which uses a High Dynamic Range Image (HDRI) to light your Bryce scene in addition to traditional Bryce lighting. Currently, Bryce will only import .hdr format HDRI images created using a light probe (spherical).

If you try to open a .hdr file in a format that Bryce can't use, you will get the following error message:

Click on OK and load an HDR file compatible with Bryce.

To use Image Based Lighting:

1. Display the Sky & Fog palette by clicking the Sky & Fog button at the top of the Bryce window.
   
   
2. Click the Sky Lab button. The Sky Lab dialog appears.
   
   
   Click the IBL tab.
   
   
3. Enable the Use HDRI Image option.
   
   
   
   By default, when you enable the use of an HDRI image, Bryce disables the Sunlight and turns off any Atmospherics that were selected, like Fog and Haze.
4. Click on Edit, the Open dialog comes up. Locate and select a .hdr image, click on Open.
   
   Please note that In the current version, Bryce accepts pictures in a square aspect ratio in the radiance .hdr format. It can correctly map "Angular Map" or - as they are also called "Light Probe" - projections.
   
   
   
   The HDRI preview thumbnail will look similar to the following, along with the image showing in the Sky preview thumbnail:
   
   
   
   If the HDRI preview thumbnail doesn't show the image, disable the Use HDRI Image option, then enable it again.
   
   If the Sky preview thumbnail doesn't show the image, disable the Render HDRI Image as Background option, then enable it again.
   
   
5. To use the IBL but not render the image as the background, disable the Use HDRI Image as Background option.
   
   
6. The Disable Sun Light option will automatically be disabled when an HDRI image is loaded, as will Fog and Haze. To use Fog and Haze, click on the Atmosphere tab and re-enable the options. Re-enabling Fog and Haze will help add more realism to the scene.
7. Adjust the IBL settings as needed.

• Roller Ball - Controls the orientation of the HDRI around the X and Y-axes.
• X - degrees of rotation around X axis
• Y - degrees of rotation around Y axis
• The "cross" on the Roller Ball indicates where the horizon is on the HDRI sphere in the North position. The sun spot indicates the center of the light probe. Rotate the Roller Ball to rotate the HDRI around the light probe sphere. Holding down Ctrl while rotating the ball to constrain the rotation to around the Y-axis only. The X and Y values update as the ball is rotated and changing the numbers moves the ball to the appropriate orientation.
  
  
  
  
  
  
• Quality - The number of lights used to render IBL. This control ranges from 16 to 4096.
• Intensity - This controls the exposure level of the HDRI. This affects both the light emitted from the HDRI for lighting with IBL and the image when rendered in the background. Exposure is not linear, rather it is exponential. See this website for a better explanation: http://freespace.virgin.net/hugo.elias/graphics/x_posure.htm. This control ranges from 0 to 100.
• HDRI Effect - This controls the intensity of lights when using an HDRI for IBL. This is just like changing the intensity of any light object in Bryce. This will only affect light intensity during IBL. It will NOT affect the look of HDRI rendered in the background. This control ranges from 0 to 100.
  
  A large HDRI needs considerable computer power and the controls may appear to react very sluggishly or not at all. Be patient or use a smaller HDR image (800 x 800 instead of 1600 x 1600, for example).
  
  
  
  Any objects with specularity will need to be modified to use reflection instead. Either that or increase the specularity range of the material. Refer to "IBL in a Nutshell" for more information on this.
• Radius - This controls the distance of the lights (used for IBL) from the center of the Bryce universe. This is only important if falloff is set to Linear or Squared. The radius will have to be quite small if falloff is used at all since light falls off rather quickly with both of these formulas. Play with the control and see how low it needs to be to get some light with a default Bryce scene.
• Falloff - Determines the type of light falloff to be used
• None – light never falls off due to distance (Radius becomes irrelevant) - Default
• Linear – light falls off as a function of distance
• Squared – light falls off as a function of distance squared (much faster than Linear)

8. Periodically, exit the Sky Lab and check the scene in the Working window to see how it looks. It may take some time to get the right settings for your particular scene. Bryce lights can also be used to enhance certain areas of the scene.
   
   When checking the scene in the Working window, do not rely on the Nano Preview for the lighting since it may not accurately preview the IBL-enabled image. Instead, render the scene, with or without AA, to get a better idea of the current settings.

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