Live Stacking

Live stacking turns every incoming sub into a growing, ever-cleaner image while you shoot. Instead of judging the night from single noisy frames, you watch the target emerge in real time — faint arms and shells appearing sub by sub. The stacking runs on the rig itself, so it keeps accumulating whether the app is open or not.

Arm it

Open the Stack tab and arm the stacker — one tap. From then on, every frame the rig captures feeds the stack:

• During a sequence — arm it before or mid-run; sequence subs are stacked as they land.
• During loop or manual captures — framing and testing frames stack too.

Disarm the same way when you’re done, or leave it running all night.

What happens to each sub

Every incoming frame goes through the same pipeline on the rig:

1. Quality gates. The frame’s HFR and star count are checked first. A cloud-softened or trailed sub is dropped, not averaged into your data — the panel counts drops so you can see how picky the night is being.
2. Star alignment. Accepted frames are registered against the stack with a full similarity fit — translation, rotation, and scale — so the stack stays sharp even as the field drifts or rolls.
3. Sigma-clipped integration. Outlier pixels (satellite trails, cosmic ray hits, hot pixels) are rejected statistically as the frame merges into the accumulated stack.

The result: signal-to-noise climbs with every accepted sub, and one bad frame can’t smear the whole night.

Reading the panel

The Live Stack panel shows the running state of the night:

• Subs / dropped — how many frames are in the stack, and how many the quality gates rejected.
• HFR — the sharpness trend of incoming frames.
• Field roll — the measured rotation between subs. This one is a free diagnostic: on an equatorial mount, steady field roll is the signature of polar misalignment, so the readout doubles as a polar-drift meter. If roll keeps accumulating, your polar alignment deserves a second look.

The stack chip

While a stack is live, the viewer switches to showing it automatically and displays a “Stack · N subs” chip. Tap the chip to flip between the running stack and the latest single sub — useful for comparing what one frame sees versus what the night has built so far.

Persistence

The stack is saved to disk on the rig as a night-scoped FITS, and it surfaces in your Files tree alongside the night’s subs. Your armed intent and the list of accepted subs survive a backend restart, and the final FITS is flushed when you disarm or the rig shuts down cleanly.

Caution

The accumulating stack itself is held in memory while armed. Don’t restart the rig backend mid-night with a stack armed — the armed state and accepted-sub list survive, but the in-progress accumulation is the one thing that doesn’t. Disarm first if you need to restart.

Live stack vs. deep stack

The live stack is the instant view — tuned to show you the night as it happens. When the sequence ends, the rig automatically re-stacks the whole night with Siril into an archival master: that’s the quality pass. See Overnight Deep Stacking.