colour_hdri.photometric_exposure_scale_factor_Lagarde2014¶
-
colour_hdri.
photometric_exposure_scale_factor_Lagarde2014
(EV100, T=0.9, f_v=0.98, theta=10)[source]¶ 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.
The model implemented by this definition is appropriate to simulate a physical camera in an offline or realtime renderer.
- Parameters
T (array_like, optional) – Exposure value \(EV100\).
T – Transmission factor of the lens \(T\).
f_v (array_like, optional) – Vignetting factor \(f_v\).
theta (array_like, optional) – Angle of image point off axis \(\theta\).
- Returns
Photometric exposure in lux-seconds (\(lx.s\)).
- Return type
ndarray
Notes
The saturation based speed, \(S_{sat}\), of an electronic still picture camera is defined as: \(S_{sat}=\cfrac{78}{H_{sat}}\) where \(H_{sat}\) is the minimum focal plane exposure, expressed in lux-seconds (\(lx.s\)), that produces the maximum valid (not clipped or bloomed) camera output signal. This provides \(1/2\) “stop” of headroom (41% additional headroom) for specular highlights above the signal level that would be obtained from a theoretical 100% reflectance object in the scene, so that a theoretical 141% reflectance object in the scene would produce a focal plane exposure of \(H_{sat}\).
Scene luminance \(L\) scaled with the photometric exposure value computed by this definition is almost equal to that given by the
colour_hdri.saturation_based_speed_focal_plane_exposure()
definition.
References
Examples
>>> EV100 = exposure_value_100(8, 1 / 250, 400) >>> H = photometric_exposure_scale_factor_Lagarde2014(EV100) >>> print(H) 0.0002088... >>> H * 4000 0.8353523...