The HDR merge has the same cause as the panorama: its result took the
reference frame's colour tags, and a raw whose white balance is only in the
vendor's multipliers (CR2, NEF, ARW...) has no AsShotNeutral in them.
merge_hdr now takes the median multipliers of all its inputs (the rule of
consensus_multipliers: the mean of the middle two for an even count; missing,
non-finite and non-positive values do not vote) and sets the result's
AsShotNeutral to their reciprocal, as stitch does. With no multipliers (DNG
sources) the reference frame's tags are kept, as before. HdrResult carries the
multipliers so that the brackets of an HDR panorama vote as frames of their own
when the merged brackets are stitched (the engine passes them on).
In the app and the CLI the neutral from starting_colour_tags (#965) is already
there for frames balanced alike, so those renders do not change.
Tests: an HDR merge of raw-style frames gets the median AsShotNeutral (odd and
even counts, missing and unusable multipliers ignored) and the written DNG says
it; without multipliers the reference frame's colour is unchanged.
A raw whose white balance is only in the vendor's multipliers (CR2, NEF, ARW...)
has no AsShotNeutral of its own. Loading a frame dropped the multipliers and
stitch copied the first frame's colour tags, so a panorama of frames that reach
the stitcher without a neutral wrote a DNG with neither AsShotNeutral nor
AsShotWhiteXY, and a viewer had no white to start from (a strong colour cast
until White Balance > Auto).
Frames now carry the multipliers (Frame::wb_multipliers, filled from the decoded
raw; load_frame_with is split so a decoded raw can be tested without a file).
stitch takes the median R/G and B/G of the multipliers of the frames that are in
the panorama (the mean of the middle two for an even count; frames without
multipliers, or with non-finite or non-positive ones, do not vote) and sets the
result's AsShotNeutral to their reciprocal, green = 1. The source's
AsShotWhiteXY is dropped with it: a reader takes it before the neutral and the
DNG spec makes the two exclusive. With no multipliers anywhere (DNG sources) the
first frame's tags are kept, as before.
In the app and the CLI a raw without colour matrices already gets a neutral from
starting_colour_tags (#965). For frames balanced alike the new neutral renders
the same (checked in the engine crate); it differs when the camera balanced the
frames differently: the panorama follows the median instead of the first frame.
Tests: the frame carries the multipliers; the consensus for odd and even counts,
with missing and unusable values; stitching raw-style frames gives the median
AsShotNeutral, ignores frames outside the panorama and leaves the colour as it
was without multipliers; the written DNG, read back with the raw reader, has the
reciprocal AsShotNeutral and the white balance the source's multipliers give.
eliets2