colour_hdri.luminance_to_exposure_value

colour_hdri.luminance_to_exposure_value(L, S, k=12.5)

Computes the exposure value \(EV\) from given scene luminance \(L\) in \(cd\cdot m^{-2}\), ISO arithmetic speed \(S\) and reflected light calibration constant \(k\).

Parameters

• L (array_like) – Scene luminance \(L\) in \(cd\cdot m^{-2}\).

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

• k (numeric, optional) – Reflected light calibration constant \(k\). ISO 2720:1974 recommends a range for \(k\) of 10.6 to 13.4 with luminance in \(cd\cdot m^{-2}\). Two values for \(k\) are in common use: 12.5 (Canon, Nikon, and Sekonic) and 14 (Minolta, Kenko, and Pentax).

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

>>> luminance_to_exposure_value(0.125, 100)
0.0