colour_hdri.illuminance_to_exposure_value

colour_hdri.illuminance_to_exposure_value(E, S, c=250)[source]

Computes the exposure value \(EV\) from given scene illuminance \(E\) in \(Lux\), ISO arithmetic speed \(S\) and incident light calibration constant \(c\).

Parameters

  • E (array_like) – Scene illuminance \(E\) in \(Lux\).

  • S (array_like) – ISO arithmetic speed \(S\).

  • c (numeric, optional) – Incident light calibration constant \(c\). With a flat receptor, ISO 2720:1974 recommends a range for \(c\). of 240 to 400 with illuminance in \(Lux\); a value of 250 is commonly used. With a hemispherical receptor, ISO 2720:1974 recommends a range for \(c\) of 320 to 540 with illuminance in \(Lux\); in practice, values typically are between 320 (Minolta) and 340 (Sekonic).

Returns

Exposure value \(EV\).

Return type

ndarray

Notes

  • The exposure value \(EV\) indicates a combination of camera settings rather than the focal plane exposure, i.e. luminous exposure, photometric exposure, \(H\). The focal plane exposure is time-integrated illuminance.

References

[Wikipediaa]

Examples

>>> illuminance_to_exposure_value(2.5, 100)
0.0