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Exposure Controls

Exposure controls are plug-in components that adjust the output levels and color range of a rendering, as if you were adjusting film exposure.

  • Default menu: Rendering menu > Environment > Environment and Effects dialog > Environment panel > Exposure Control rollout
  • Alt menu: Rendering menu > Environment and Effects > Environment and Exposure Settings > Environment and Effects dialog > Environment panel > Exposure Control rollout

The exposure control process is known as tone mapping. These controls are especially useful for renderings that use radiosity or that render high-dynamic-range (HDR) imagery.

Exposure control compensates for the limited dynamic range of computer displays, which is typically about two orders of magnitude: The brightest color that appears on a display is about 100 times brighter than the dimmest. The eye, by comparison, can perceive a dynamic range of about 16 orders of magnitude. In other words, the brightest color we can perceive is about 10 million-billion times brighter than the dimmest. Exposure control adjusts colors so they better simulate the eye's great dynamic range, while still fitting within the color range that can be rendered.

Left: Linear exposure control maps intensity evenly.

Right: Logarithmic exposure control maps most intensities to low and mid tones.

Tips:

  • If the primary lighting from your scene comes from standard lights (rather than photometric lights), use the Logarithmic exposure control and turn on Affect Indirect Only.
  • Use Automatic exposure control for rendering still images. This method is also useful for first-draft renderings.
  • Use Logarithmic or one of the advanced exposure control for animations with a moving camera. Automatic and Linear exposure control with a moving camera can cause excessive flickering.
  • For outdoor scenes that use the Daylight system, turn on the Exterior toggle to prevent overexposure.
  • When using an OCIO-based mode for color management, the tone map is provided by the view transform. In general, it's best to use <no exposure control>. For more details, see Exposure and Color Management.

Exposure and Attenuation for Standard Lights

When you use standard lights that are not attenuated, renderings tend to have a low dynamic range, because light intensities don't vary greatly across the scene. In this situation, adjusting light values might be all you need to do to get a good rendering.

On the other hand, when lights are attenuated the illumination might be too bright on near surfaces or too dim on distant surfaces. In this situation, the Automatic exposure control can help, because it adjusts the larger dynamic range of the (simulated) physical scene, into the smaller dynamic range of the display.

Topics in this section
  • Exposure Control Rollout
    Chooses the exposure control to use, and provides a preview.
  • Automatic Exposure Control
    Automatic Exposure Control samples the rendered image and builds a histogram to give good color separation across the entire dynamic range of the rendering. It can enhance some lighting effects that would otherwise be too dim to see.
  • Linear Exposure Control
    Linear Exposure Control samples the rendered image and uses the average brightness of the scene to map physical values to RGB values. Linear Exposure Control is best used for scenes with a fairly low dynamic range.
  • Logarithmic Exposure Control
    Logarithmic Exposure Control uses brightness, contrast, and whether the scene is outdoors in daylight to map physical values to RGB values. You can use it with the default scanline renderer. Logarithmic Exposure Control is best for scenes with a very high dynamic range.
  • Physical Camera Exposure Control
    Sets exposure for Physical Cameras, using an Exposure Value and a color-response curve.
  • Pseudo Color Exposure Control
    Pseudo Color Exposure Control is actually a lighting analysis tool that provides you with an intuitive way of visualizing and evaluating the lighting levels in your scenes. It maps luminance or illuminance values to pseudo colors that show the brightness of the values being converted. From darkest to brightest, the rendering shows blue, cyan, green, yellow, orange, and red. (Alternatively, you can choose a grayscale where the brightest values are white, and the darkest are black.) The rendering includes the colored or grayscale spectrum bar as a legend for the image.
  • Lighting Data Exporter Utility
    The Lighting Data Exporter renders the active viewport to images that include luminance and illuminance data that can be used for lighting analysis.
Parent topic: Cameras

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