What's New in Version 2.1
2026-09-25
Version 2.1 is the largest SUNSCAN update since launch. It touches all three layers of the project: the mobile app, the SUNSCAN firmware and its web interface. Highlights: upload your images to SpectroSolHub straight from the app, a scan assistant that tells you when to observe and guides you while you place the disk, spectral line identification on the live image, connecting the SUNSCAN to your home Wi-Fi, recording without dropped frames, much faster processing and a new interface.
✨ At a glance
SpectroSolHub upload: share your images with the community straight from the app.
Gallery filters: by spectral line, by processing state and by SpectroSolHub upload.
Hε images computed automatically from Ca II H scans.
Spectral line on stacks and animations, inherited from their scans and editable.
Line name in the watermark of every image of a scan.
Scan assistant: scan duration, best time window, and live guidance to place the disk.
Spectral line identification: line names shown directly on the live image.
Live disk preview while recording and automatic scan stop.
Real progress for processing, stacking and animations, step by step.
Connect the SUNSCAN to your home Wi-Fi, with automatic discovery on the network.
Auto exposure and a completely rebuilt focus assistant.
Channel advice in cropped mode: the app tells you whether red, blue or all three channels will give the better scan.
Performance: no more dropped frames while recording, faster processing, smoother live preview.
One-tap firmware update, offered as soon as the SUNSCAN connects.
New interface, in the app and in the SUNSCAN web interface.
🔭 Acquisition
Scan assistant ("Assist." button)
Before the scan, the assistant uses your GPS position and ephemerides. It gives you the scan duration, the Sun's tilt, the quality of the observing window at that time (ideal, good, usable, strongly tilted…) and the best time slot. It also tells you when the Sun is below the horizon, and asks for your GPS position if it does not have one.
Placing the disk: the assistant guides you live to position the disk along the slit, so that it stays centred for the whole transit. The prompts are explicit: "Centre the Sun on the slit to start the guidance", "Bring the disk to the mark (16.4)", then "In position, let the Sun drift off upstream, then record".
While recording, a gauge shows the remaining time and tells you when the disk has finished passing.
Live disk preview
While the scan runs, a thumbnail shows the solar disk building up column by column. You know straight away whether the scan is good, without waiting for processing.
Automatic scan stop
Stop the recording a few seconds after the disk has left the slit. And if you forget, the automatic stop takes over: once the disk has finished passing, a 30 s countdown starts and recording stops on its own. Tap the countdown to cancel it if you want to carry on. It is on by default and can be turned off in the Settings.
Spectral line identification ("Ident." button)
In full-frame mode, mono or colour, the app recognises which part of the solar spectrum is on screen: rather like plate solving, but for the spectrum. Line names appear directly on the image, and the labels follow the zoom:
solar lines in amber;
telluric lines in blue;
key lines in colour (Hα, Na D, Mg b, Ca II H & K…).
A banner shows the wavelength range, the dispersion (Å/px) and the number of lines identified. If identification fails, it explains why: not enough light, saturation, focus…
Auto exposure ("AUTO EXP" button)
In full-frame colour mode, exposure time adjusts itself. The setting is remembered, and exposure is locked as soon as you start recording.
Typing the exposure time (short press on "EXP")
In cropped mode, where exposure time is set entirely by hand, a short press on EXP opens a numeric keypad: type the value in milliseconds (0.1 to 30,000 ms) instead of hunting for it with the slider. Handy for returning to exactly the exposure that worked, from one session to the next.
A short tutorial introduces the two EXP gestures (short press to type, long press to change range) the first time you open the settings in cropped mode.
Channel advice (cropped mode)
The SUNSCAN builds its mono frame from the camera's Bayer matrix, either by summing the four photosites of each cell or by keeping a single colour. The right choice depends on where in the spectrum the grating points, and it matters: far in the red, at Hα, the green and blue photosites see next to nothing, so summing them in adds their noise and none of their signal. The red channel alone then makes the better scan. At the blue end, at Ca II H and K or Hγ, the blue channel wins. In between, at least two colours answer and the sum of the four photosites is the one to use.
In cropped mode, the app looks at how the light splits between the three colours and tells you. A banner appears above the image, with three dots and the advised colour lit:
Signal mostly in the red: "Tap to switch to the red channel".
Signal mostly in the blue: "Tap to switch to the blue channel".
Signal spread over several colours: "Tap to switch to all three channels (RGB)".
Tapping applies the change, the cross dismisses the banner. The advice only shows when the channel in use is not already the right one.
Nothing has to be identified for this: how the light splits between the three colours is enough, and it is read off the per-channel Max ADU measured on the raw frame, before the channel is picked. The advice therefore does not depend on the channel in use.
Three safeguards: no advice when the signal is too faint for the ratios to mean anything; none either on a clipped frame, unless one colour leads by a wide margin anyway; and three identical readings in a row are needed before any advice appears, so that a cosmic ray or a cloud edge cannot change its mind. Once a channel is advised, it stays advised until the gap narrows appreciably, which keeps the advice from flickering near the limit. When the Sun leaves the slit, the last advice stays on screen.
Focus assistant, completely rebuilt
Percentage bar of the best score, in green, orange or red.
Curve of the last 20 seconds.
"New best!" indicator.
Reset button.
3-step guide.
The score is smoothed: one lucky frame no longer sets an unreachable record.
Also
New display threshold slider: finer on small values, with tick marks and a fine-adjustment mode.
Cropping: if you press REC before cropping, a bubble points you to the crop button.
REC and crop buttons: a loading indicator now appears, which prevents double taps. The recording timer has been redrawn.
Camera not connected: a clear panel appears with a "Connect camera" button, instead of an endless spinner. The phone's clock is synchronised at the same time.
End of scan: the "Scan complete" dialog has been redrawn, with the spectral line offered as coloured chips.
Fix: when storage was nearly full, it became impossible to stop the scan.
🖼️ Processing, gallery and images
Real processing progress
A progress bar now shows the current step: reading the scan, reconstructing the disk, geometric correction, then surface, continuum, prominences, Doppler and helium.
If it fails, the reason is shown, for example: scan too short, or no Sun. Processing started before you switch screens, or close the app, is picked up again automatically.
Hε images
The Hε line (3970.08 Å) sits in the red wing of Ca II H: processing a scan tagged Ca II H now automatically computes three extra Hε images (surface, colour and prominences) without changing anything else. Expect about 4 s of extra processing.
The Hε line is verified in the spectrum itself, not just from the tag: a Ca II K scan mistakenly tagged Ca II H produces no Hε images.
If you tag an already-processed scan as Ca II H, the app offers to reprocess it so you get them.
Line name in the watermark
The watermark on a scan's images now carries the spectral line after the date (for example "Ca II H line - 3968 Å") on surface, colour, negative, prominence and Doppler images, as was already the case for stacks and animations. A scan with no line, or tagged "Other", keeps the date alone.
Fix: after changing the line and reprocessing, images of the old line that do not exist for the new one (negative, colour) stayed on the SUNSCAN. They are now removed.
Stacks and animations
Real progress: a percentage bar and the current step (aligning scans, writing images, building the GIF) with the number of scans processed. Failures are handled instead of freezing the screen.
Spectral line on stacks and animations: they inherit the line of their scans when created, show its coloured badge in the gallery, and can be filtered by line just like scans. The line can be changed from the "⋯" menu, or for several items at once from the gallery's multi-selection, handy for filling in the ones created before this version.
New stacked colour images.
Stacks and animations now show the observation date (the mean time of the scans for a stack, the first scan for an animation) rather than their creation date. For those created before this version, it is still the creation date.
Actions (download, delete, and "View on SpectroSolHub" for a stack) are grouped in a "⋯" menu, as on a scan's screen.
Default duration of an animation frame: 160 ms (was 120 ms).
Fix: the "raw" colour image of a stack was in fact the enhanced image. It is now taken from the raw stack. Existing stacks are not rebuilt: stack the scans again to get it.
Fix: the negative image was generated incorrectly on stacks and animations.
Fix: the creation date of a stack or animation changed as soon as a file was added to its folder.
Gallery filters (funnel button)
In the Scans tab, filter your scans:
by spectral line (with a "No line" chip);
by state: processed, not processed, failed;
by upload: "On SpectroSolHub", "Not uploaded yet".
Each chip shows how many scans it would return. Once a filter is active, "Select all" selects every filtered scan at once, ready to stack, animate or delete.
Redesigned gallery
Pill tabs and an item counter.
Rounded thumbnails and coloured line badges.
Animated multi-selection.
A message when the gallery is empty.
Leaner scan screen: secondary actions (line, 3D view, information, processing, download, delete) are grouped in a "⋯" menu. The line is picked from the same grid of coloured chips as at the end of a scan, even with no SUNSCAN connected.
Fix: the thumbnail selection frame did not follow the image's rounded corners exactly.
Downloading images
A message is shown if a download fails. An error page is no longer saved as an image.
On iOS, images are filed in a SUNSCAN album.
Fix: zoom is reset when you move to another image.
☁️ SpectroSolHub
SpectroSolHub is the sharing platform of the spectroheliograph community. You can now upload your scans to it without going through a computer. The platform is built and offered to the community free of charge by Cédric Champeau. Many thanks to him.
Connecting your account
In Settings, SpectroSolHub section, enter your credentials. Two-factor authentication is supported. The password is never stored: the SUNSCAN exchanges it for an access token, which you can revoke from your account on the site. Settings also show the storage and image count used on your account.
Uploading a scan
On the screen of a processed scan, the cloud button opens the upload dialog:
pick the images to upload: the most useful ones are ticked by default;
check the spectral line: it is prefilled from the scan's tag, but you can correct it;
add a title and notes if you wish;
publish right away, or keep the observation as a draft and publish it later from the site.
A progress bar shows the current step and the image being uploaded. You can close the dialog: the SUNSCAN carries on, and the app picks the upload back up when you return to the scan. A brief Wi-Fi drop does not fail the upload. At the end, a button opens the observation on the site.
Each upload creates a new observation: the app warns you if the scan has already been uploaded.
Uploading a stack
The same cloud button is available on a stack's screen. For stacks created with this version, the date, line, title and a note are prefilled from the source scans: the date is the mean time of the scans (the one written in the watermark) and the observer name is the one given when stacking.
For older ones, the folder only carries the creation date, not the observation date: the app asks you for the observation date and time (UTC), prefilled with the creation date, and displays the image whose watermark holds the date so you can check it.
Uploading animations is not offered yet.
Finding your uploads and tidying up
Uploaded scans and stacks carry a small cloud in the gallery: green if the observation was published, grey if it stayed a draft. Tapping the cloud opens the observation, as does "View on SpectroSolHub" in the "⋯" menu of the scan screen. The "On SpectroSolHub" filter, also available in the stacks tab, shows only those items, useful when clearing them off the SUNSCAN. An upload that failed partway does not count as uploaded.
Everything on the Share your images page →
📶 Connectivity
Connect the SUNSCAN to your home Wi-Fi
From Settings, the SUNSCAN can join your Wi-Fi network instead of using its own hotspot:
If it fails, the SUNSCAN falls back to its hotspot on its own and the reason is shown: wrong password, network not found…
Saved networks: the SUNSCAN rejoins them automatically at startup. You can forget them from Settings, or go back to the hotspot.
Finding the SUNSCAN on the network
The "Find SUNSCAN" button locates the device automatically on your network. You can also enter its IP address by hand.
Also
Fix: the "SUNSCAN connected" state stayed on screen after a connection loss.
Fix: some phones, Xiaomi in particular, could not connect to the hotspot.
Everything on the Setup page →
⚡ Performance
No more dropped frames while recording
The SER file is now written to the SD card separately from capture. A slow SD card or a momentary stall no longer costs you frames, and writing each frame is much lighter.
If the camera is cut off mid-recording, the SER file is still closed cleanly.
Faster scan processing, identical results
The most expensive processing steps have been rewritten to run much faster on the Raspberry Pi: mean image, disk reconstruction, edge detection, circularisation and tilt correction.
Smoother live preview
Wi-Fi power saving on the Pi is disabled: it caused latency and stutter.
Capture and recording now run at high priority.
System maintenance tasks, which could saturate the SD card mid-scan, are disabled.
The gallery no longer slows capture down
Downloads are generated on the fly, without writing anything to the SD card.
Thumbnails are cached.
The gallery's disk work runs at low priority.
You can therefore download files during a scan without losing frames.
🎨 Interface and settings
New visual identity
New animated splash screen: a slit sweeps across the SUNSCAN logo before the app opens.
Unified theme with an emerald green accent.
Animations on buttons and on the navigation bar.
Harmonised dialogs.
Home screen
Redrawn graph of the Sun's path.
Solar altitude and azimuth displayed.
An alert when free space drops below 5 GB.
Firmware update
Offered as soon as it connects: when the app detects a SUNSCAN that needs updating, a dialog shows the installed version and the new one, and starts the update directly, without going through Settings. It stays optional ("Later"), but without it the app will most likely be unstable. The dialog only appears once per session.
More reliable: the app waits for the SUNSCAN to reboot and checks the installed version before announcing the result.
Settings and languages
The Settings screen is reorganised into cards, and languages are now picked with buttons.
SUNSCAN web interface, completely rebuilt
A single navigation for scans, stacks, animations and snapshots, with multi-selection, download and delete.
Full-screen viewer: zoom, rotation, FITS preview.
Choose which file types to download, with their size shown up front.
Storage and battery indicators.
Everything on the Retrieve your data page →
📱 Platform
Android: the app targets Android 16 (SDK 36), as required by Google Play.
iOS: the app asks for local network access, needed to find the SUNSCAN on your Wi-Fi.
Thanks
Special thanks to Oscar Canales, for his help and for his suggestions throughout this version.
Thanks as well to Cédric Champeau, who builds SpectroSolHub and offers it to the community free of charge.
Going further
Mobile app overview
Observe
Last updated