High dynamic range

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High dynamic range (HDR) images in general are images that have a very large contrast ratio. The data in HDR images is typically stored as floating-point values, producing very large files. Two common HDR file formats are Radiance RGBE (*.hdr) and OpenEXR (*.exr), which was developed by ILM as an open source library and has a much better compression ratio.

Unlike normal photographs, HDR images normally contain data that is linearly proportional to physical values. When taken with a calibrated camera, HDR images can contain absolute physical values, but most HDR data has some arbitrary scaling.

A typical approach to produce HDR images is to take multiple exposures with a normal camera (taken with increasing exposure times) and combine them into one HDR image, using a special software (e.g. HDR Shop, Photoshop CS2, Photomatix and many others).

The only display that comes close to displaying full HDR content is the Brightside display. Normal monitors do not have the required contrast ratio, color resolution or absolute brightness. Therefore, a process called Tone mapping is required, which is called Exposure Control within 3ds Max. That process tries to map the HDR data into a range that can be displayed on your monitor.

External links

• Making light work pt 4 by AEC Magazine
• HDRI and Caustics for the Beginner by Rick Timmons
• HDRI with 3DSMAX & Mental Ray (simple scene file for beginners) by Emre Goren
• Various .hdr setups with Max9/mental ray (simple scene file for beginners) by Jeff Patton