Dynamic Exposure in X-Plane 10

In real life, the human eye adjusts to overall light levels; the result is that a light source’s perceived brightness is partly a function of the surrounding lighting environment.  At night car headlights are blindingly bright, but during the day they are merely visible because they appear dimmer relative to the sun.  X-Plane 10 simulates this effect via dynamic exposure.

About Dynamic Exposure

X-Plane simulates dynamic exposure by decreasing the brightness of emissive (“_LIT”) textures when the sun comes out.  A computer monitor does not have the power to simulate the actual light levels of an outdoor daytime scene; instead elements of the scene that are artificially lit must be under-exposed relative to the sun to keep the balance of the scene correct. When the sun sets, the remaining artificially lit elements regain their full brightness, simulating the pilot’s eyes adjusting.

Dynamic exposure is always present in X-Plane 10 under all rendering settings; it is not necessary to turn on HDR mode to see dynamic exposure effects.

Dynamic exposure prevents overexposure artifacts when _LIT textures are used on objects at dusk or in partial sunlight.  In X-Plane 10 you can use the full dynamic range of your _LIT textures without worrying about over-saturation in the late afternoon or evening.

Dynamic Exposure for Scenery

For scenery authors, dynamic exposure is always on, fully automatic, and “just works”.  99% of the time, scenery will look better with dynamic exposure.  If you had to reduce the brightness of your _LIT textures to prevent over-exposure, you may find that this is not necessary in X-Plane 10.

Dynamic Exposure for Aircraft

For aircraft, dynamic exposure is an “opt-in” feature: you enable dynamic exposure on a per-OBJ basis by checking the “dim LIT” check-box for that object in Plane-Maker’s “misc objects” screen.

When “dim LIT” is unchecked, the attached object does not receive dynamic exposure processing, and LIT textures will appear exactly as they did in X-Plane 9.

When “dim LIT” is checked, the lit texture will have its brightness reduced when the sun is out.

Usage tips:

  • Turn “dim LIT” on for baked lighting where the baking would look too strong during the day.  For example, landing light spill baked onto the fuselage in a LIT texture should have “dim LIT” turned on.
  • Turn “dim LIT” off for panel elements that need to be visible to the pilot during the day.  For example, gear indicator lights implemented via an OBJ should not be “dim LIT”.

Dynamic Exposure and the 2-d panel

Pre-made instruments on the panel pick for themselves whether to participate in dynamic exposure; most do not because they need to be visible during the day.

For generic instruments, there are multiple lighting modes that let you pick whether dynamic exposure is applied. The naming convention is a little bit odd:

  • Instruments with “auto” do not have dynamic exposure.  The idea is that the instrument simulates a photo cell automatically turning up the brightness of the instrument during the day.  The instrument is “automatic” –  the user does not have to turn up the brightness to compensate for dynamic exposure.
  • Instruments with “manual” do have dynamic exposure.  The instrument’s simulated brightness is constant, and thus it looks less bright when the sun is out.  The user will have to manually adjust the brightness as the time of day changes.

The 2-d panel spills (-2, -3, -4) are always subject to dynamic exposure.

Dynamic Exposure and the Panel Texture

When you use a panel texture in a 3-d cockpit, dynamic exposure is not re-applied to the panel – instead, you get the same dynamic exposure effects that you would get if the panel texture were used directly as a 2-d panel.

Dynamic Exposure and ATTR_lit_level

Dynamic exposure works after ATTR_lit_level directives in an OBJect. During the day, ATTR_lit_level with a value of 1.0 will not be the full texture brightness for objects subject to dynamic exposure.

Some of the datarefs often used for brightness now come in two variants in X-Plane 10: variants for automatic exposure and variants for manual exposure.

sim/cockpit2/electrical/panel_brightness_ratio
sim/cockpit2/electrical/panel_brightness_ratio_auto
sim/cockpit2/electrical/panel_brightness_ratio_manual
sim/cockpit2/electrical/instrument_brightness_ratio
sim/cockpit2/electrical/instrument_brightness_ratio_auto
sim/cockpit2/electrical/instrument_brightness_ratio_manual
sim/cockpit2/electrical/instrument_brightness_ratio
sim/cockpit2/electrical/instrument_brightness_ratio_auto
sim/cockpit2/electrical/instrument_brightness_ratio_manual

The “auto” datarefs automatically compensate for dynamic exposure, and thus match the “auto” brightness settings on generic instruments and are easily visible during the day.  The manual brightness ratios do not compensate and will appear dimmer.  The non-labeled datarefs are from v9 and provide “auto” behavior for compatibility.

“Auto” datarefs may have light levels larger than 1.0 during the day; this is normal.

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