The desktop app

valerian-gui does everything the command line does in one window, with the same five steps in the same order: Calibrate, Register, Stack, Process, Export. It is laid out like Helia's, in Valerian's own colours: a night sky, and an optional red night-vision palette for use at the telescope.

The pictures on this page are the real window, drawn by the program's own tests from real data: a monochrome H-alpha session of the California Nebula (five 300 s lights, with darks, flats and dark flats) and a one-shot-colour Seestar session of IC 5070 (sixty 10 s frames). A first session runs the same two sessions on the command line.

A whole session is walked through in the tutorial, and every control is in the desktop app reference.

The window

• Top bar: the logo and name (click either for the About page, or press F1), the file that is open, and the buttons Night (the red palette, F2), GPU (the benchmark), Open (Ctrl+O) and About. A Recent menu lists the images opened lately.
• Workflow rail (left): the five steps, numbered and joined by a line. Each shows where it stands (Optional, Ready, Running, or Done with a tick and what it produced) and a hint. Click a step to open its panel. Below 900 pixels wide the rail shrinks to the numbers.
• Panel (right): the open step's name, what it is for, and its controls. Drag its edge to resize it.
• Notice strip and view (middle): what is running or has just happened, then the picture with its zoom controls, then the histogram.

The five steps

1. Calibrate

Names a folder of lights and, optionally, folders of darks, flats, dark flats and bias frames (or one master file in place of a folder), and a folder for the result. Calibrate lights combines each kind of calibration frame into a master, builds the pixel map and writes every calibrated light, with the masters in a masters folder inside, like valerian calibrate (How calibration works). The viewer shows the first calibrated frame.

Leave the step alone when the frames are already calibrated, as a Seestar's are.

2. Register

Finds the stars in every frame, picks the sharpest as the reference and writes every frame aligned to it, like valerian register (How registration works). Stack registers by itself, so this step is for when you want the aligned frames as files, to check them or to use another program. The folder defaults to the Calibrate output.

3. Stack

Registers and combines a folder of frames into one picture with outlier rejection, like valerian stack (How stacking works). The folder defaults to the last step's output; the rejection is automatic unless you choose one. Raw colour frames are demosaiced first. The stack is written as a FITS file and opened for the Process step, so one button takes you from sixty raw frames to a picture you can stretch.

The Drizzle chip in this step combines dithered frames onto a finer grid instead; see How drizzle works.

4. Process

Works on the open image, which is never changed: every tool edits its settings in the panel, previews on a reduced copy, and writes a new FITS file when you ask. The chips at the top of the panel choose the tool:

• Stretch: curves, levels and an automatic-stretch preview. See How stretching works.
• Star removal: remove the stars, look at the starless image, the stars and the mask, reduce instead of remove, and save both layers. See How star removal works.
• Plate solve: find where the image points from its header or a position you type, circle the matched stars, and save the world coordinates. See How plate solving works.
• Colour: calibrate the white balance against Gaia star colours, compare with the original, and save the result. See How colour calibration works.

To work on a file you already have, press Open (or Ctrl+O), type a path and press Open in the panel, drop the file on the window, or start the program with the file name: valerian-gui file.fits. The view is a reduced copy (1600 pixels on the long side); the black and white points are measured on the full frame and the real work runs on the full image when you apply.

5. Export

Writes the open image as 32-bit FITS, unstretched and with its header, or as an 8-bit PNG drawn with the stretch chosen in Process, for sharing. The name defaults to <name>_export.fits beside the image, and the extension follows the format.

The view

The picture is drawn from a reduced copy, so its zoom is in screen pixels per pixel of that copy (100 % is one for one; the toolbar names the copy's size).

• Scroll over the picture to zoom about the pointer, or press + and -.
• Drag to pan. A double click, or the percentage button, fits the picture to the window again.
• The histogram under the picture is of what is drawn, per colour (grey for a mono picture), on a log scale, with the median level at the right. The Histogram button hides it.

Plate solving and colour calibration draw circles on the stars they matched or used; they follow the zoom.

Notices

Whatever is running is announced above the picture: a spinner, what is being done, how many frames of how many it has done (with a bar), the seconds it has taken and the latest line the step reported (the frame being registered, its stars and its seeing). The window stays usable while it works. A finished step says what it did and has a Dismiss button; an error stays until you dismiss it. A running step has a Cancel button in the notice (Esc does the same): it stops within a frame, band or plane, keeps nothing and leaves the output folder as it was. See Cancelling a running step.

Night vision

Night (or F2) swaps every colour for red on black, and draws the picture and the logo in red only, which keeps dark-adapted eyes dark-adapted. The choice is remembered.

Choosing files

Every place the app reads or writes a file has a native file dialog, the operating system's own (the common dialog on Windows, the desktop portal on Linux), so the usual places, recent folders and bookmarks are there:

• Open in the top bar (or Ctrl+O) opens an image. It starts in the folder of the image already named and shows FITS files.
• Choose... beside each folder box of Calibrate, Register and Stack picks a folder, and Save as... beside each output path (Stack, Stretch, Star removal, Plate solve, Colour, Drizzle and Export) chooses where the result is written. It offers the name the box holds, starts in its folder and adds .fits when the name has no extension. Cancelling the dialog leaves the box as it was.
• Choose catalogue... in the Plate solve panel picks a .vcat star catalogue.
• Choose folder... in the Drizzle panel picks the folder of frames to drizzle.

The path boxes still work for typing or pasting a path, and the dialog runs beside the window, which stays responsive while it is open.

Shortcuts

The GPU and the About page

GPU in the top bar opens a graphics adapter, times the calibration, warp and combine kernels against the CPU code on frames of a size you choose, and shows how well they agree. See The GPU kernels. Any step on the rail leaves it.

About (the logo or the name, or F1; Esc closes) leads with the dedication, then the version and build record (with a button that copies them for a bug report, and one that opens the GPU adapter and adds it), the copyright, the licence, the additional terms, a link to 12hobbies.studio under "More from Laurence Horrocks-Barlow", and the third-party licences when the list ships beside the program.

valerian-gui -V prints the name and version and valerian-gui --version adds the notices, both without opening a window.

Background extraction (valerian background) is on the command line and is not in the window yet. The screenshots in this manual are made by the GUI tests (see Building and testing).