- Quick averages every frame. Use it to check a session fast.
- Quality is the default. It rejects outliers like satellite trails and leaves out the weakest tenth of your frames.
- Max Detail uses finer alignment and leaves out the weakest fifth. Use it for your best data.
- You pick a mode, not a method. The app sets everything else.
1. The three modes side by side
- Quick
- Average of every frame. Standard alignment. Keeps all frames. The app estimates about a minute.
- Quality
- Kappa-sigma rejection. Standard alignment. Keeps the best 90% of frames. The app estimates about five minutes.
- Max Detail
- Kappa-sigma rejection with more passes. Finer, slower alignment and colour-channel alignment. Keeps the best 80% of frames. The app estimates fifteen minutes or more.
- Same in every mode
- Automatic star detection and alignment, calibration frames if you add them, and the same finishing tools afterwards.
Times depend on how many frames you have, how big they are and which iPhone or iPad you use. “Best frames” means the frames in which the app found the most stars, which usually means the sharpest and clearest ones.
2. Quick: a fast first look
Quick adds every frame together and takes the average. Averaging is the cleanest way to reduce random noise when every frame is good, and it is the fastest.
- Use it to check that a new set of frames aligns before you commit to a longer stack.
- Use it in the field to see whether focus and framing are working while you can still fix them.
- Avoid it when a plane, satellite or passing cloud crosses any frame. An average keeps a faint copy of everything.
3. Quality: the everyday default
Quality uses kappa-sigma rejection. For every pixel, it looks at the values across your frames, drops any that sit too far from the rest, and averages what’s left. A satellite that crosses one frame is an outlier at those pixels, so it is usually rejected.
Quality also leaves out the tenth of your frames with the fewest stars before stacking. That quietly removes the shaken, hazy or badly focused shots most sets contain.
4. Max Detail: for your best data
Max Detail runs the same rejection with more passes and a tighter threshold, uses bicubic interpolation when it shifts frames into line, and aligns the colour channels too. It keeps the best 80% of frames.
- Use it for a long, well-focused session you plan to finish carefully or print.
- Use it when bright stars show red or blue fringes after a Quality stack. Max Detail lines up the colour channels separately.
- Skip it for a small set. With 8 frames, leaving out the weakest fifth means stacking only 7.
5. Which mode should you pick?
- First stack of a new set
- Quick, to check alignment and framing.
- Most night-sky sessions
- Quality. It handles trails and weak frames without you sorting them.
- Your best night of data
- Max Detail, then compare it with the Quality result.
- Fewer than 10 frames
- Quick or Quality. There’s little to gain from leaving more frames out.
A failed or cancelled stack doesn’t use one of your 3 free stacks a week, so it’s safe to try. If a stack stops with “Not Enough Usable Stars”, read how to fix it.
What the modes don’t change
No mode turns alignment off, and you can’t choose Median, Maximum or the weighted methods by hand. That means star-trail images aren’t possible yet. For the theory behind each method, see how astrophotography stacking works.
Want better frames to stack in the first place? Read how to get the best results from Astro Stacker.