# Exposure Computation¶

## Common¶

colour_hdri

 average_luminance(N, t, S[, k]) Computes the average luminance $$L$$ in $$cd\cdot m^{-2}$$ from given relative aperture F-Number $$N$$, Exposure Time $$t$$, ISO arithmetic speed $$S$$ and reflected light calibration constant $$k$$. average_illuminance(N, t, S[, c]) Computes the average illuminance $$E$$ in $$Lux$$ from given relative aperture F-Number $$N$$, Exposure Time $$t$$, ISO arithmetic speed $$S$$ and incident light calibration constant $$c$$. luminance_to_exposure_value(L, S[, k]) Computes the exposure value $$EV$$ from given scene luminance $$L$$ in $$cd\cdot m^{-2}$$, ISO arithmetic speed $$S$$ and reflected light calibration constant $$k$$. illuminance_to_exposure_value(E, S[, c]) Computes the exposure value $$EV$$ from given scene illuminance $$E$$ in $$Lux$$, ISO arithmetic speed $$S$$ and incident light calibration constant $$c$$. adjust_exposure(a, EV) Adjusts given array exposure using given $$EV$$ exposure value.

## Digital Still Camera Exposure¶

colour_hdri

 focal_plane_exposure(L, A, t, F, i, H_f[, …]) Computes the focal plane exposure $$H$$ in lux-seconds ($$lx.s$$). Computes the arithmetic mean focal plane exposure $$H_a$$ for a camera focused on infinity, $$H_f << H$$, $$T=9/10$$, $$\theta =10^{\circ}$$ and $$f_v=98/100$$. Computes the Saturation-Based Speed (SBS) focal plane exposure $$H_{SBS}$$ in lux-seconds ($$lx.s$$). Computes the exposure index values $$I_{EI}$$ from given focal plane exposure $$H_a$$. exposure_value_100(N, t, S) Computes the exposure value $$EV100$$ from given relative aperture F-Number $$N$$, Exposure Time $$t$$ and ISO arithmetic speed $$S$$. Converts the exposure value $$EV100$$ to photometric exposure scale factor using Lagarde and de Rousiers (2014) formulation derived from the ISO 12232:2006 Saturation Based Sensitivity (SBS) recommendation.