What is Pixel Repair and should I leave it on?
Leave it on. Pixel Repair ships enabled for both hot and cold on every stack.
What it does
Section titled “What it does”Pixel Repair cleans stationary sensor defects, hot pixels and cold pixels, in each frame individually. It runs after calibration and before warping, so a defect is fixed in the frame’s own geometry rather than smeared across the output canvas by the warp.
A statistical pass finds a pixel that sits far above (hot) or below (cold) its immediate neighbors, judged against the local MAD. A star core is not mistaken for a hot defect: an isolation guard checks the pixel against its second-highest or second-lowest neighbor too, and a real star’s point-spread function lifts the neighbors along with the core, so the margin never clears. A defect stands alone; a star does not.
Whenever a frame has a dark master assigned, a second pass runs alongside the statistical one: it checks the sites the dark itself flags as defective and adjudicates each one against the light, using a more sensitive threshold since it already has independent evidence the site is bad. This guided pass only touches frames with a dark master; a frame with no dark relies on the statistical pass alone.
Screenshot: The Pixel Repair block in the integrate panel with hot and cold enabled.
Why it runs before rejection, not instead of it
Section titled “Why it runs before rejection, not instead of it”Sigma clipping and Linear Fit Clipping (see rejection and normalization) reject outlier samples pixel by pixel across the stack, but their budget of iterations and tolerance is finite. A stationary defect sits at the same coordinate in every frame, so rejection cannot vote it out the way it votes out a trail or a transient that only touches one or two frames. Cleaning defects before the combine means rejection spends its passes on the things only rejection can fix: trails, cosmic ray hits, and other one-off transients.
The thresholds
Section titled “The thresholds”Three MAD-sigma controls sit under the two toggles, all shipped at defaults tuned for typical sensor noise:
- Hot σ, the statistical hot-pixel threshold. Default 6.
- Cold σ, the statistical cold-pixel threshold. Default 6.
- Guided σ, the dark-guided pass’s threshold at dark-flagged sites. Default 2.75, tighter than the statistical passes because the dark master already supplies independent evidence.
Raise Hot σ or Cold σ if repair is eating real signal, a dense star field losing tight cores despite the isolation guard, or a nebula’s brightest knot reading as a defect. Lower them if a rig runs unusually thermally stable and known bad pixels are slipping through at the default margin. Guided σ rarely needs touching: it only matters on frames with a dark master, and loosening it starts trusting sites the dark flagged but the light doesn’t clearly corroborate.
Where the controls live
Section titled “Where the controls live”The Pixel Repair block sits in the settings column of the integrate panel, alongside rejection, normalization and quality weighting. Settings there are per stacking session; use stack presets to carry a tuned set of thresholds across targets on the same rig.