Verify the pixel-area treatment in JPEG resampling

Verify directly whether JPEG pixel values produced by the Lightroom rendering are interpolated from RAW data without rescaling for the change in pixel area caused by geometric distortion.

Background

The comparison between JPEG and RAW images assumes that JPEG resampling preserves the signal corresponding to the RAW pixel solid angle at the mapped position, rather than rescaling the signal to the JPEG pixel’s altered solid angle. The agreement of corrected JPEG and RAW radial indices provides indirect support, but the rendering behavior has not been directly established. This matters for deriving diffuse-emission surface brightness and field-dependent corrections from JPEG data alone.

References

We have not verified this assumption directly; it is supported by the agreement of the corrected JPEG-based indices with those from the RAW data within 0.07 in the green channel (Section~\ref{sec:decomposition}), although the change of pixel area by the distortion correction is only a few percent even at the corners.

— 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 Appendix A, “Geometric Mapping between the JPEG and RAW Images”