In Unreal Engine version 4.19, the Level Editor exposure control has been changed for an EV100
slider and a game settings check-box in the view mode menu. When Game Settings
is checked, the level viewport will use the in-game setting configuration for exposure behavior (see next section). Otherwise, the EV100 slider allows a user override, with a range of -10
, supporting very dark to very bright scenes, using realistic scene illumination.
For other viewports than the level viewport, the "Game Settings" check-box is replaced by an "Auto" check-box and implements an automatic exposure behavior.
The in-game settings for exposure are controlled within the post process settings. In 4.19, some options have been renamed but otherwise previous settings are compatible. The following image shows the three metering mode supported, as well as which options are enabled in each mode and their default settings.
Auto Exposure Histogram behaves as the previous histogram mode. Auto Exposure Basic is the previous basic mode, with the addition that the calibration constant is now exposed in the advanced tab. The Calibration Constant defines the target average brightness of the image after exposure, and is used for white balancing.
Otherwise, 4.19 adds a new metering mode named Manual, where the value of the camera exposure is defined by new camera settings: Shutter Speed (1/t), ISO (S) and Aperture (N). The formula used to compute the camera exposure scale is :
- Exposure = 1 / (1.2 * 2^EV100)
- EV100 = log2( N²/t * 100/S )
here defines the relationship between the scene surface luminance (L in cd/m²) and pixel brightness (B), before the tonemapper and exposure compensation (see below) are applied:
This can be verified by disabling the tonemapper through the show flags and inspecting the scene brightness with the pixel inspector. Note that the EV100 editor overrides set directly the EV100 in this equation.
At last, the Exposure Compensation camera setting defines an additional scale of (2^ExpComp) on top of the exposure computed from the current metering mode, except when using the EV100 Editor overrides.