The limit is EXCLUSIVE inside Jungfraujoch - the first value that is no longer a count - and NXmx
saturation_value is INCLUSIVE, the highest value that still is one. XDS OVERLOAD and the DIALS
trusted_range read it inclusively too. The write side subtracted the count and no read side added it
back, so the value fell by one on every write-read-write cycle, unbounded: four chained runs over one
dataset gave 32766, 32765, 32764, 32763. It also fed the preprocessor, so one more real count was
called saturated after each cycle.
SaturationValueFromLimit / SaturationLimitFromValue now carry the conversion, used by the writer and
by all three readers (HDF5, the lite receiver, the viewer). JFJochReaderImage's summation test moves
from > to >= in the same commit: it was silently compensating for the missing count, and correcting
one without the other would have shifted it instead.
Two more places said the wrong thing about the same pixels:
error_value was GetUnderflow(), which is -1 for an unsigned image - a value no unsigned pixel can
hold. The marker those images really carry is UINTx_MAX, and GetImageFillValue() already returned it,
so the class held two disagreeing definitions of one marker.
bit_depth_readout is now written for unsigned images only. DIALS remaps the top two codes of
2^bit_depth_readout to -1 and -2 whenever the field is present, without looking at the pixel type.
For an unsigned image those fall below underload_value and are masked, which is what we want. For a
signed one they land INSIDE the trusted range, so a saturated pixel reached DIALS as a trusted count
of -2 - on the strongest reflections. Verified with DIALS 3.27: an int32 file now masks both
sentinels. The field stays where it earns its keep, since dxtbx cannot read unsigned 32-bit without
it.
Neither the values themselves nor the wire format change. Verified against NXmx, DECTRIS SIMPLON,
Durin (Global Phasing fork), XDS and DIALS 3.27; the chained run now holds at 32766.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VfYvJT5Nb71suJCowRBn5z
leonarski_fandClaude Opus 5
eb0cb42355