Lnexposure

Lnexposure is the natural logarithm of the exposure E that reaches a camera sensor during an exposure. In imaging, exposure E is proportional to scene luminance L, the exposure time t, and the aperture-transmission factor, often simplified as E ≈ k·L·t. Lnexposure is defined as ln(E), yielding a value in which multiplicative changes in E become additive changes in lnexposure.

Because ln(a·b) = ln a + ln b, lnexposure decomposes variations in exposure into additive components: ln(L), ln(t), and a constant accounting for system gain. This property makes lnexposure convenient for statistical modeling and for linearizing certain sensor or scene effects in log-domain processing.

Lnexposure is related to exposure value (EV). EV is a base-2 logarithm of exposure ratios; lnexposure uses the natural logarithm. They are proportional, differing by a constant factor equal to ln(2). In practice, lnexposure and EV convey similar information about scene exposure, modulo reference scaling.

Applications include analysis of exposure in HDR reconstruction, exposure normalization across images, and feature engineering for machine learning in vision tasks. In log-domain pipelines, lnexposure helps stabilize variance and simplifies modeling of multiplicative lighting changes.

Measuring lnexposure requires calibrated exposure data or a reliable model of the camera response. It is independent of gamma corrections but sensitive to the camera response function and noise; comparisons across devices require a shared reference E0 and consistent calibration.

See also: exposure, exposure value, log-luminance, HDR imaging, camera response function.