Lucky imaging,in one application.

Why planetary work is a different problem

Deep sky imaging fights photon noise: the signal is faint, so you integrate for hours to accumulate it. Planetary imaging has the opposite problem. Jupiter is bright enough to expose in milliseconds, and what ruins the picture is not noise but the atmosphere - several kilometres of moving air between the planet and the sensor, smearing the detail differently in every frame.

The answer is lucky imaging. Record thousands of very short frames, and the turbulence will have been briefly kind in a few hundred of them. Find those, align them, average them and sharpen the result. Nothing from a deep sky workflow transfers: there are no stars to register on, quality means sharpness rather than star shape, and the final image lives or dies on the sharpening rather than on the integration.

That is why planetary processing has traditionally meant a separate set of programs, and usually several of them: one to pre-process the capture, one to grade and stack, one to sharpen and one to derotate. Each is free. Each has its own conventions, its own file expectations and its own place to go wrong at eleven at night. Akastroid does the common path in one place.

Grading: finding the frames the seeing left alone

Every frame in the capture is scored, and the measurement is more careful than it looks. The obvious approach - Laplacian energy, the standard focus measure - gets planetary frames backwards, because a Laplacian responds most strongly to the highest spatial frequency present, and in a short planetary exposure that is read noise. Score frames that way and the noisiest frame wins.

So the measurement is the structure at the scales a planet's detail actually occupies, divided by the noise in that same frame, and it is restricted to the region around the disc so that empty sky cannot dilute it. What comes out is a ranking that matches what your eye would pick if you had the patience to flick through seventeen thousand frames.

You choose what percentage to keep. A graph of the whole capture shows how the seeing changed while you were recording, which is worth reading on its own: it tells you whether to record for longer next time, or to wait an hour for the planet to climb.

Multi-point alignment, which is the whole game

Aligning frames on the planet as one rigid object is not enough. The atmosphere does not shift the disc, it warps it - the equatorial belt moves one way while the polar region moves another, within the same frame. Stack that as a rigid object and you get a sharp limb and a mushy middle, and no amount of sharpening recovers what the misalignment averaged away.

Akastroid tracks the disc in pieces on a grid you can set, so the local warping comes out before anything is averaged. This is the single setting that separates a soft planetary stack from a sharp one, and it is the reason a capture can look disappointing in one program and detailed in another with identical source data.

The surviving frames are then averaged, not sigma clipped. Once the bad frames have been culled the survivors differ only by noise, and a plain mean extracts the most signal from them - clipping here would throw away good data to solve a problem that grading has already solved.

If your planet is undersampled - and at a few hundred pixels across, most are - the integration is done onto a finer grid, recovering detail below the original pixel scale from the sub-pixel shifts between frames.

Dispersion correction

The atmosphere refracts blue light more than red, so a planet low in the sky arrives on the sensor as three slightly separated images. It shows as a blue fringe on one edge and a red fringe on the other, and it is the most common reason an otherwise good capture looks wrong.

Red and blue are realigned to green before sharpening. Done afterwards, sharpening has already amplified the fringes into something no alignment will remove cleanly.

Sharpening you can actually steer

The stack is sharpened per scale: six sliders from finest to coarsest, each with its own noise suppression, so you can lift the fine detail in the cloud belts without amplifying the grain that lives at the same frequency. Adjustments re-apply instantly, because changing them does not rebuild the stack - the expensive work was done once.

There is also deconvolution, which measures the blur from the planet's own limb and partly undoes it. It is applied before sharpening and it is deliberately conservative: deconvolution invents plausible detail when it is pushed, and a planet has no star in frame to check the answer against, which is why the control starts low and the guidance on it says to raise it slowly and compare.

The Moon and the Sun

Lunar captures take the same path. The Moon's advantage is that it is bright and full of contrast, so grading has plenty to work with; its difficulty is that it fills the frame, which is exactly where multi-point alignment earns its keep - seeing varies measurably across a field that wide.

Solar captures work the same way, in white light or hydrogen alpha, with a choice of how the result is presented: a warm near-white as the eye sees it through a safe filter, the deep orange-gold that hydrogen alpha is conventionally shown in, or the recorded channel with no tint applied at all. The palette is a presentation choice made explicit, not a filter pretending to be data.

Both are covered in the guides as photography rather than as software: photographing the Moon and photographing the Sun.

What this replaces, and what it does not

The usual planetary chain is four programs: one to pre-process and centre the capture, one to grade and stack, one to sharpen, one to derotate a long session. Akastroid covers the common path through that chain in a single window, with the capture, the grading graph and the sharpening sliders all on screen at once.

It is worth being straight about the other side. AutoStakkert and RegiStax are free, mature and very good at what they do, and there are corners - unusual derotation workflows, exotic capture formats, specific manual controls - where they go further. Somebody already fluent in that chain has no particular reason to change. What is on offer here is one application instead of four, on a Mac as well as a PC, with the frame selection and the sharpening in the same place so you can go back and forth between them without exporting anything.

Deep sky too

The same application handles nebulae, galaxies and clusters from FITS or camera RAW, with calibration, star registration through field rotation, gradient removal and photometric colour. If that is what you are here for, the deep sky page covers it in the same detail.