Environment Reflection Maps

 Available in Krakatoa v1.5.0 and higher

Introduction

• Krakatoa can use the Environment Map found in the 3ds Max Environment Dialog as an additional light pass by looking up texels of the map along the particle Normals (if a valid Normals channel is provided).

Enabling Reflection Mapping

To enable Environment Reflections, the following steps must be performed:

• A valid Texture Map must be placed in the Environment Map slot of 3ds Max. It should be set to an Environment Projection mode, typically Spherical.

• The >Use Environment Reflection option should be checked in the Main Controls rollout.

• Enabling Reflections will add the Normal channel to the list of Memory Channels in the Channels rollout. The particles must provide their own Normals:
  • PRT Volume particles will acquire the Normals from the closest surface point of the source volume automatically.
  • PRT Loader can acquire Normals from Culling geometry even if no culling is performed.
  • Particles from Geometry Vertices will use the Vertex Normals of the source mesh.
  • PFlow particles will generally store the X axis of their transformation matrix as the Normal. The particles can be oriented using various Operators including Rotate>Speed Follow or the dedicated Krakatoa Geometry Lookup Operator which can acquire Normals from the closest point of a selected geometry surface.
  • Other particles (Legacy, TP) will use the X axis of their transformation matrix.

Controlling HDRI Exposure

• When using a High-Dynamic Range Image (HDRI, EXR) as the Environment Map, the Default Exposure of the source might be too high.
• There are several approaches to tweaking the Environment Reflection intensity:

Changing RGB Level

• If the bitmap is being loaded with Default Exposure, or the image is not an HDRI and there is no exposure control in the I/O plugin, you can use the RGB Level rollout of the 3ds Max Bitmap Texture to scale the input linearly:

Changing Black And White Point

• The preferred approach to scaling the input values is to use the built-in Exposure Controls of the Image Loader plugin (HDRI or EXR).
• Other than the RGB Level value, it scales the values logarithmically, producing much better results.
• The images below use a White Point of 7,6,4 and 2 respectively:

Mixing The Two Approaches

• The RGB Level value can still be used AFTER the image has been scaled by the loader to tweak the final intensity:
• The Black and White Points in the HDRI I/O Setup Dialog provide means to control the exposure:
• The following images show the Bitmap loaded with Black Point of -3 and White Point of 2.0
• From left to right - Isotropic shading with No Environment Reflections, RGB Level of 1, 2 and 3:

Using Color Correct Map

• To modify the exposure of the Environment Map interactively inside of 3ds Max, you can also employ the ColorCorrect Map (the free ColorCorrect by Cuneyt Ozdas for earlier versions of 3ds Max, or the built-in one in 3ds Max 2009 and higher).