Browser GUI walkthrough

The primary GUI is the local browser app (mcf.gui() / mcf-web). Both GUIs drive the same McfSession. Desktop twin: mcf.gui_qt() (PySide6).

pip install "multicolorfits[all]"   # or [web]
mcf-web                            # opens http://127.0.0.1:8321
# python -c "import multicolorfits as mcf; mcf.gui()"

Preload:

import multicolorfits as mcf
mcf.gui(files=['a.fits', 'b.fits'], colors=['#C11B17', '#4CC417'], labels=['Hα', 'OIII'])
# mcf.gui(state='session.json')

Choosing a browser

By default the GUI opens in your system default browser. To pick one explicitly:

mcf-web --browser firefox
mcf-web --browser google-chrome
mcf-web --no-browser          # print the URL only; open it yourself

mcf.gui(browser='firefox')
mcf.gui(browser='google-chrome')
mcf.gui(open_browser=False)   # then visit the printed http://127.0.0.1:… URL

Names are those understood by Python’s webbrowser module (firefox, google-chrome, chromium, safari, …), or a full path to an executable. On Unix you can also set the BROWSER environment variable for the default case (no --browser / browser=).

For Jupyter / Colab embedding see gui_notebook_embed.

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Layout

Region	Purpose
Left column	Image panels (stretch, color, levels, header, clear/remove)
Right compose tabs	Compositing / Colors / Axes / Canvas
Combined view	Fast preview (downsampled, on by default) or full WCS plot
Action bar	Plot Full Resolution, session save/load, Save Image/FITS, Export transparent, Export Script, Reset

Header toggles: Auto-refresh previews, Full-res panel previews, and light/dark theme (?theme=light\|dark also works for screenshots).

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Image panels

1. Load FITS via path, folder browse, or upload (web).

2. Set stretch, hex color, label, vmin/vmax or percentile sliders, optional smooth.

3. Use Zscale / Min/Max as needed; Header to inspect/edit cards.

4. Default is four panels. Click + Add panel for more (up to 16), or Remove on a panel you no longer need.

Layers must share a pixel grid. When they do not, a warning bar offers Align layers… (needs [reproject]) — reproject onto the reference panel or into ICRS / Galactic / …

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Compose tabs

• Compositing — mode (rgb, lab, hsv, hsl, ryb, cmyk), blend (Lab family), background (black / white / transparent / custom), gamma. Gamma applies to the combined image; left-panel thumbnails intentionally ignore it.

• Colors — curated palette apply, hue tune wheel, color-vision safety report.

• Axes — WCS tick style, title, labels, legend, combo swatch, band labels.

• Canvas — facecolor (incl. transparent), overlays (compass / beam / scale bar when [overlays] is installed).

Mode dropdown (same session, different combine strategies):

Fast preview (checked by default) updates the combined view from the same downsampled buffers as the left panels — good for stretching, colors, mode, and gamma. Click Plot Full Resolution when you want the publication WCS figure (axes, overlays) used by Save Image / Export Script.

Backgrounds and RYB paint

These three panels are what the Compositing tab is driving (same linear stretch for a fair RGB vs RYB comparison):

See also Backgrounds and RYB paint mixing and Color-space compositing suite.

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Save and export

See save_and_export and saving_outputs:

• Save Session… → JSON (paths + settings)

• Save Image… → format from extension

• Save FITS… → RGB cube + provenance

• Export transparent… → RGBA stamp

• Export Script → recreation .py

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Qt desktop GUI notes

Same session model and most controls. Browser tends to get new features first. The Qt combined canvas keeps the matplotlib navigation toolbar; panel previews are simpler QLabels.

More Qt / classic result shots: Gallery.