[Bug]: Clipped red RAW photosites cause bright red speckles in full-resolution trichrome rendering (0.67.0) #1611

NegPy version / build

0.67.0

OS

macOS Tahoe 26.4.1

Scanner

Digital camera (macro/copy setup)

Scanner model / details

Nikon Z7II + Nikon NIKKOR Z MC 105mm f/2.8 VR S, tethered via usbc

Light source

Jack Whittaker Big Scanlight, sequential RGB/trichrome scanning

Correction mode

Off

Input ICC profile (if any)

none/default

Relevant process-tab settings

no changes

What happened

Issue

I'm seeing bright red (occasionally white) pixel-sized speckles, primarily in dark areas of converted trichromatic scans.

The artifacts are absent from NegPy's normal preview, but appear with Preview Export Size and in exported Flat/Print TIFFs and JPEGs. However, exporting a Linear 16-bit TIFF and inverting it in Photoshop produces a clean image.

RawDigger confirms approximately 0.2% clipped red photosites (26,000 pixels), with no clipping in the other channels. Their distribution matches the speckles.

I likely made a calibration mistake by selecting a film-base patch near the edge of the frame, potentially affected by vignetting. This may explain the red-channel clipping, but I wouldn't expect NegPy's interpretation to turn such limited clipping into these conspicuous red artifacts, especially when the Linear TIFF can be inverted cleanly in Photoshop.

Troubleshooting

None of the following helped:

• Disabling sharpening, chroma denoising, and crosstalk correction
• Testing all available export demosaicing methods (VNG made the artifacts worse)
• Disabling GPU acceleration
• Exporting JPEG at 100% quality or 16-bit TIFF

Questions

1. Could NegPy's full-resolution density normalization or color processing be amplifying clipped pixels into bright-red speckles?
2. Why does the normal preview remain clean while full-resolution rendering shows these artifacts?
3. Could this be handled more gracefully even when the original RAW contains some clipped pixels?

Source file

Zipped RGB NEFs: https://drive.google.com/file/d/1ZzWr43AXq84TKzpLddjXGXh9KcHkidTr/view?usp=sharing

Screenshots

No response