Photographic Exposure Control

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The mr Photographic Exposure (mrPE) control was added to 3ds Max 2008. Internally, it is using the mia_exposure_photographic shader introduced by mental images in 2006.

It's purpose is to tone map a rendered image. This process can be compared to choosing a certain exposure in a conventional still camera, to adjust your camera to very dark or very bright situations by selecting exposure time, aperture and film sensitivity (ISO/ASA).

In contrast to other tone mappers in 3ds Max (e.g. the Logarithmic exposure control), the mr Photographic exposure control uses parameters closely related to traditional photography. Note that although mrPE has parameters for shutter speed, aperture and film speed, these parameters are redundant and are all collapsed into one Exposure Value (EV).

Normally, you need to use tone mapping when you have an image that is brighter than your monitor can display. For example, when using a skylight system that uses physically accurate light intensities diet pills, you get an almost purely white image without tone mapping.

Since rendering normally happens diet supplements in linear color space, gamma correction is an important part of tone mapping, especially since most monitors have a non-linear response curve (i.e. a pixel RGB value is not proportional to the brightness is produces on screen).

Notes on using mr Photographic Exposure control

• If gamma correction is disabled in 3ds Max, mrPE automatically applies a gamma=2.2 correction. That means that it will take what the renderer produces and apply a gamma=2.2 curve to the data.

• Be careful as the preview doesn't take into account the gamma correction even if enabled in max. The preview is shown in linear, without gamma. Hence the preview is always darker than the final image. This seems to be a bug in Max 2009.

• If you, for some odd reason, explicitly want to work "wrong" and without gamma, you can set the "midtones" in the photographic exposure control to 0.4545 which precisely counteracts the built in gamma of 2.2.

• If "Burn" = 1.0 and your "Shadows" = 0, mrPE amounts to a linear scale of values; depending on the global gamma settings, it might also add a gamma=2.2 curve.

• Zap Anderson has posted a scripted plugin for 3ds Max 2008 that creates a new "physical" camera with parameters for f-stop and shutter speed. These parameters are connected to the mrPE speed/aperture parameters, to a depth-of-field effect and to the motion blur parameters, resulting in physically plausible camera effects.

External links

• Detailed documentation can be found in the Architecture & Design documentation by mental images
• Zap Anderson discusses the difference between physical and old-school lighting with respect to the exposure control in his blog and how this affects background images, for example. Just to make sure everybody understand this, he has added another blog entry titled Why does mental ray render black? Undestanding the new Physical Scale settings