Astro: from frames to the final image

Night & Astro takes your lights, darks, flats and bias through stacking, plate solving and colour to a finished picture, with the stars on their own layer. Info shows the steps in order, each with a tick when it is done.

The guided steps

In Night & Astro, Modify > Info shows a numbered strip:

1. Frames: what you imported, sorted by type.
2. Calibrate & stack.
3. Mosaic (mosaics only).
4. Plate solve & annotate.
5. Develop: background, colour, stretch and star separation.
6. Export.

Each step says what it needs and has a button for its action. A single nightscape photo starts at step 4.

images/screenshots/11_astro_steps.jpg

1. Import and sort the frames

1. Choose Night & Astro as the mode.
2. Import your lights together with the darks, flats, bias and dark flats. They can have any names and sit in any folders. FITS, camera raw, TIFF and JPEG all work.
3. After a moment the status line says, for example, "Astro frames sorted by their headers and pixels: 20 lights, 10 darks, ...". The kind chip says Astro stack (or Astro mosaic for several fields).
4. Check Info > Frames & Calibration. It lists the groups ("20 lights, 120 s, gain 139, -10 C, filter Ha") and warns in orange about mismatches: darks of the wrong exposure, gain, ISO or temperature, or no flats for a filter. Hover a frame to see why it got its type.

How the sorting works: three votes decide each frame's type: the FITS frame type in the header, the pixels (stars mean a light; no stars and a low level mean a dark or bias; no stars and a high level mean a flat) and the file and folder names. Very short dark-like frames are bias; frames matching the flats' exposure with no light are dark flats.

Override: pick a type in a frame's drop-down (Automatic, Light, Dark, Flat, Bias, Dark flat), or tick several frames and press Mark as: Dark (or any type). Each change is one undo step and is saved with the project.

2. Calibrate and stack Night & Astro Pro

Stacking works at full resolution: every light is read again at its full size as linear data (FITS with its Bayer pattern, camera raw before white balance, other formats with the sRGB curve undone), so hundreds of frames fit in a few gigabytes of memory.

1. Under Stack frames in the Night & Astro inspector, choose the rejection method (sigma clipping or winsorised sigma clipping) and its kappa, and tick Calibration frames, Weight frames and Leave out bad frames as you need.
2. Press Stack frames. PanoRyse builds master bias, dark (scaled by exposure), dark flat and flat frames by a sigma-clipped median, and calibrates each light: the dark is subtracted and the result divided by the normalised flat, before debayering.
3. The lights are registered on their stars and weighted by their noise, sharpness (FWHM) and star count. Frames spoilt by cloud or trailing are left out, each with its reason.
4. The rejection removes satellite trails, aircraft and hot pixels that appear in only some frames. Only the lights are stacked. A progress bar shows each stage, and Cancel stacking stops it and leaves the project unchanged.
5. Tick Show the frame report to see each frame's stars, FWHM, sky level and weight, and why any frame was left out.
6. If you set up a tracker log (see trackers), its motion limits guide the registration.

For scale: 50 phone raw files of 12.6 megapixels with a master dark stack in about 19 seconds, and 130 frames of 24 megapixels in about 80 seconds within about 4 GB of memory, on an 8-thread computer. AI Assist and the MCP server stack with panoryse_stack_frames.

3. Plate solve Free

1. Press Plate-solve in the step, or open Info > Plate Solve & Sky.
2. PanoRyse detects the stars and matches their patterns against the built-in Hipparcos catalogue. Fields of about 6 degrees and wider solve with no hint at all.
3. For a telescope or long lens (under 6 degrees), install the deep star catalogue pack and give an approximate centre (or let the FITS header give it).
4. When it solves, constellation lines and star names are drawn through the fitted solution, and the catalogue names the field.

Writing the solution into files (FITS WCS, XMP) and showing the photo's outline in the Sky Atlas belong to Night & Astro Pro.

4. Auto colour (astro) Free

Open Modify > Develop and the section Astro: Stars & Stretch. Under AUTO COLOUR (ASTRO):

1. Press Measure. The readout shows the sky's R, G and B, with a neutral or cast badge.
2. Choose the steps: 1 Remove the gradient (off by default; tick it for light-polluted frames), 2 Neutralise the background, 3 Calibrate the colour and 4 Set the black point.
3. Set the Background level (default 0.030; Pure black sets 0) and the clipping budget.
4. Press Auto colour (astro). Each step shows its measured numbers and is its own undo step.

What the steps do: gradient removal subtracts a smooth model down to the darkest sky, so nothing is lifted; neutralisation lowers each channel to the darkest; colour calibration scales the channels (never offsets them) so a Sun-like star is white, using the plate-solved stars' catalogue colours when available; the black point puts the sky at your chosen level, clipping at most the budget.

images/screenshots/07_nightscape_auto_colour.jpg

AI Assist does the same from "make the sky black" or "fix the colour".

5. Separate the stars Night & Astro Pro

1. In Astro: Stars & Stretch, under STAR SEPARATION, choose the engine: Classic (today's default) or Learned (with the learned star remover pack).
2. Press Separate Stars (or Separate stars into layers in Image Layers). When it finishes, Image Layers shows Base, Starless and Stars, with Stars hidden and Starless selected: the screen shows the starless nebula and the header says "Editing: Starless layer".
3. Edit the nebula: Basic, Tone Curve, HSL, Colour Grading and the stretch change only the Starless layer.
4. Click the eye on Stars to put the stars back (Screen blend; at 100 % it gives back exactly the original). Select Stars to grade only the stars, or lower its opacity for quieter stars.
5. Use the refine brushes if a star was missed or a nebula knot taken. Both engines remove the faint diffraction-spike traces of the brightest stars.

images/screenshots/10_astro_star_layers.jpg

Which engine? The classic engine is fast and removes small, sharp stars best. The learned engine keeps nebulosity and grain best on smooth, well-sampled data, leaves no traces of diffraction spikes, and takes a few seconds longer (about 6 seconds for 24 megapixels on 8 threads).

6. Stretch

• Generalised Hyperbolic Stretch (GHS) Night & Astro Pro in Astro: Stars & Stretch: with the Starless layer selected it stretches only the nebula, so the stars stay small.
• Asinh and automatic screen stretch are free. A FITS display stretch never changes the data that stacking and plate solving read.

7. Satellite trails Night & Astro Pro

Detection finds straight satellite, aircraft and meteor trails in a stack or a single photo, and leaves stars, diffraction spikes and the Milky Way alone. Removal subtracts each trail's own profile, so the stars it crossed stay. With current orbital elements (downloaded from CelesTrak only when you click Download satellite data) and a plate solution, Identify names the satellites. For several frames of one field, stacking with sigma clipping is the better route.

8. Export

Export a 16-bit TIFF or 32-bit linear EXR master, a JPEG to share, or a layered Photoshop PSD that keeps Base, Starless and Stars as layers. See Export.