mental ray Architectural and Design Visualization Shader Library

Chapter 4Camera- and Exposure Effects4.1 Tone MappingWhen rendering physical light levels one runs into the problem of managing the HDRI outputof the real physics vs. the limited dynamic range of computer displays. This was discussed inmore detail on page 4.Going from this......to this.There are numerous shaders and algorithms for doing “tone mapping” (this is a very activearea of research within the CG industry), and the architectural library provides two: One verysimple shader that simply adds a knee compression to “squash” over-brights into a manageablerange, and a more complex “photographic” version that converts real photometric luminanceswith the help of parameters found on a normal camera into an image.These shaders can be applied either as a lens shaders (which will tone map the image “on thefly” as it is being rendered) or as output shaders (will tone map the image as a post process).Since both of these tone mappers affects each pixel individually 1 , the former method (as lensshader) is encouraged, since it applies on the sample level rather than the pixel level.1 Many advanced tone mappers weight different areas of the image against other areas, to mimic the waythe human visual system operates. These tone mappers need the entire image before they can “do their job”.