Frequently asked questions
Short answers, with a link to the page that has the whole story. Problems with a particular message or picture are in Troubleshooting.
Getting it
Where do I download it? Releases are not public yet: Helia is in early access, so contact 12hobbies.studio. See Download and verify.
Is it free? Yes: GNU General Public Licence version 3 or later, with additional terms under section 7 that keep the copyright line and the dedication. See About.
Which systems? Windows 10 and 11 (x86_64), Linux x86_64 and aarch64 (including Raspberry Pi 4 and 5 on a 64-bit system) are published. macOS and Windows on ARM are built from source. See Installation.
Why does it say pre-release? It is below version 1.0. The features in this manual work and are tested; some planned ones (derotation, drizzle) are not built yet. See the roadmap.
Using it
Do I need a GPU? No. It uses one when it finds one and otherwise runs on the CPU with the same results. See GPU acceleration.
What do I record? SER, 16-bit if possible, short exposures, many frames. See Capturing for Helia.
Can I use a phone video? Yes, with ffmpeg installed. See MP4 from a phone.
How many frames should I keep? The recommended share for the filter (25 or 30 per cent) is a good start. Fewer is sharper and noisier. See Stack.
Which channel, or band, should I use for my filter? Let Helia choose: it reads the filter from the file name, folder or sidecar and applies the preset below. The choice follows which pixels of a colour sensor the light reaches. On a mono camera none of this applies.
| Filter | Colour plane stacked | Frames kept | Why |
|---|---|---|---|
| H-alpha | red | 25% | 656 nm is deep red; green and blue pixels add noise, not detail |
| Ca II K, Ca II H | blue | 30% | violet light reaches the blue pixels; the line is faint |
| Mg I b | green | 30% | 517 nm is green; the line is dim |
| Na I D | green | 12% | the filter leaves the blue pixels empty, and averaging them in prints the mosaic over the granulation; green is two pixels in four |
| He I D3 | all three combined | 25% | 587.6 nm is shared between red and green |
| H-beta | blue | 30% | 486 nm reaches the blue pixels; faint |
| White light | all three combined | 12% | the continuum carries all three colours; shows granulation |
Name another plane with --channel r|g|b|lum. A plane that turns out to be clipped
is replaced by the next one (see
The red channel is clipped),
unless you named it. The reasons, with the numbers, are in
Colour presets. One caution: the 2022 captures that
were first taken for sodium were later identified, from their plane statistics, as
H-alpha (red clipped, blue empty, prominences in red; pull request #128, which corrects
those labels). The sodium choice of green therefore rests on those captures, not on a real
Na D filter, and no true sodium capture is in the test set yet. If your Na D result
looks wrong, try --channel lum and --channel r and compare.
My image looks soft. Check the seeing, then the share of frames kept, then the alignment points, then sharpen. See The stack looks soft. Wavelets that behave like RegiStax's are in progress under issue #131; Helia does not promise the same look yet.
The red channel is clipped, or the disc is a flat white plate. The exposure was long enough to push the red pixels to the sensor limit. Helia stacks the next plane by itself unless you named one. See The red channel is clipped.
Which sharpening method? Wavelets, at the recommended values, almost always. See Sharpen.
Does it change my captures? No. It only reads them.
Can I get the picture without colour? Yes: pick Mono in the Colour step, or export FITS, which is mono for a filter stack (and a red, green, blue cube for a true-colour one).
What is the colour, really? A convention. Narrow-band solar data is one colour of light; orange for H-alpha, violet for calcium and so on are for sharing. See Colourising.
Why is the FITS not sharpened? It is for measurement and further processing. Turn
on Edit the FITS too (or --sharpen-fits) if you want it sharpened.
Privacy and network
Does Helia use the network? Only when you send feedback. The stacker and the
desktop app otherwise make no network connections of their own; links open in your
browser only when you click them. The feedback client, in the app and as
helia feedback, connects to the feedback service when you press Send (or run the
command) and at no other time. helia serve listens where you tell it, on the
loopback interface unless you say otherwise. See Send feedback.
Does it send usage data? No. There is no telemetry.
Problems
A grid across the picture. Fixing a Bayer grid.
It picked the wrong filter. Press the right one on the Quick stack card, or add
--preset. See Troubleshooting.
The sharpening looks overdone. Turn it down: it is. See Troubleshooting.
Where do I report a bug? See Send feedback.