AutoExposure

The scene's exposure, as a component.

local id = entity.spawn("exposure").id
entity(id).component.add("AutoExposure", {
    auto = true,
    targetGrey = 0.18,
    meter = "centre",
})

The image stops being a fixed mapping from light to pixels: a dark interior opens up, a step into sunlight settles down, and the transition takes the time it takes rather than happening between two frames.

compensation is the manual half — stops applied on top of whatever adaptation is doing, which is the knob for exposing a shot for its shadows or its highlights. It works with auto off, as a plain exposure offset.

Every field is live: edit one in the inspector and exposure follows. With auto off and compensation at 0 the passes are released entirely.

speedUp and speedDown name the direction exposure moves. Exposure rises when the scene has gone darker, and that is the slower default on purpose: the eye adapts to darkness far more slowly than to light.

The component ticks adaptation itself, so nothing else has to drive it.

The fields

compensation, minEV and maxEV are in stops, and a stop is a power of two: +1 doubles the light reaching the image, +8 multiplies it by 256. The defaults are the neighbourhood to author in; the accepted range is the width of what the frame can represent, and a value outside it is refused naming the field and the range.

field	what it is	default	accepted
auto	Whether exposure follows the scene on its own.	true	—
compensation	Manual exposure in stops, on top of any adaptation.	0	-12..12
targetGrey	The luminance adaptation aims to put the metered average on. 0.18 is photographic middle grey.	0.18	0.001..1
minEV	The floor adaptation may stop the image down to, in stops.	-4	-12..12
maxEV	The ceiling adaptation may open the image up to, in stops. A maxEV of 8 permits 256x of adaptation gain.	4	-12..12
speedUp	How fast exposure RISES, per second, when the scene has gone darker.	0.6	0 or above
speedDown	How fast exposure FALLS, per second, when the scene has gone brighter.	2.5	0 or above
meter	Which part of the frame is read.	"centre"	full / centre / spot
meterRadius	How wide the metered region is, where 1 reaches the middle of an edge and the corners sit near 1.42, so 2 covers the whole frame.	0.6	0.001..2

minEV and maxEV bound the adaptation alone — how many stops it may move away from the exposure the scene is lit for. A scene stepping between an interior and daylight is served a stop or two either side of the defaults; a ceiling several stops above them hands adaptation a gain large enough to carry the whole frame to white, which is a picture the scene is not lit for rather than a fault in a material or a render pass.

For code that changes exposure at runtime, reach for @builtin::systems.exposure.exposure — same options, no component.

The full description of what each knob does and how the passes work is in the package readme: guides { path = "systems/exposure" }.