Photoshop's 16-bit PSBs can mark the merged transparency only by naming it
"Transparency" in the alpha channel names (positive Lr16 layer count, no Mt16).
The importer read it as a user alpha channel, and the next save wrote a second
one. merged_has_alpha now also accepts that name when the layers sit in a
global Lr16/Lr32 block and the names cover every extra channel.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
The merged image carries its transparency in the first extra channel
when the layer count is stored negative, or when a "Saving Merged
Transparency" global block (Mtrn, Mt16, Mt32) is present. Photoshop
saves 32-bit documents the second way: a positive layer count, Mt32,
and a fourth channel named "Transparency" (psd-tools transparentbg).
merged_has_alpha only knew the first, so opening such a file added a
"Transparency" alpha channel to the document, and the oracle compared
it as if it were opaque white (83.7 % of pixels off; now 0.9 %, all on
the shape's edge).
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
* Preserve HDR range in float adjustments and stack statistics
* Cover HDR exposure round trips and Levels record order
* Report the backend used by GPU parity tests
* Compare float PSD oracles at native depth and preserve signed Exposure
* Retain merged alpha metadata when decoding float references
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Co-authored-by: Brandon Thomas <echelon@gmail.com>
