A linear DNG in and out: the writer, and a three-sample RawImage

dr-export gains write_linear_dng — LinearRaw, DNG 1.4, u16 samples at
the sensor's scale, the body's matrices with their illuminants, the
as-shot neutral, the EXIF block an export writes — streamed strip by
strip through a closure so the composite is never held (FR-MRG-11). The
tiff crate's directory is a map, so PhotometricInterpretation is written
over what new_image set, which is the trick the S15.1 spike thought it
had to hand-roll around. The test reads the file back through rawler.

dr-decode's RawImage carries samples_per_pixel (a linear DNG is 3), the
body's profile with its calibrations mapped back to EXIF illuminant
codes, and the cleaned make and model. The GPU uploads a three-sample
image as it is, normalised by black and white like a photosite, through
a full f16 conversion — subnormals kept, because a 14-bit LSB sits at
f16's smallest normal and rounding it to zero would crush exactly the
shadows the file was written to keep.

core/dr-export/Cargo.toml

@@ -38,4 +38,7 @@ dr-gpu.workspace = true
 dr-pipeline.workspace = true
 env_logger.workspace = true
 pollster.workspace = true
+# The DNG writer's test reads its output back through the decoder the
+# library uses, which is the whole claim the writer makes (S15.1).
+rawler.workspace = true
 zune-jpeg.workspace = true