Quantify the effect of HE* compression on faint RAW signals

Determine the effects of Nikon Z9 HE* (High Efficiency*) non-reversible TicoRAW compression on faint astronomical signals in the RAW data, for which direct evaluation remains unavailable.

Background

The Artemis II camera RAW files were recorded using Nikon’s HE* compression, which is non-reversible. The analysis found no evidence of compression artifacts based on stellar linearity and agreement between exposures with different signal levels, but these checks do not directly measure how the codec affects faint diffuse signals. Establishing this effect would be important for assessing the reliability of consumer-camera RAW measurements of low-surface-brightness emission.

References

possible effects of the HE$\ast$ compression on faint signals could not be evaluated directly, but the linear response of the stellar signals (Section~\ref{sec:starcal}) and the agreement of all results between the two frames, whose signal levels differ by a factor of three, show no evidence of them.

— Revisiting the Optical F-corona from the Artemis II Total Solar Eclipse with RAW Data: How Far Can Consumer JPEG Images Be Trusted for Astronomical Photometry?  (2610.20194 - Tsumura et al., 14 Oct 2026) in Section 2.2, “RAW data”