Settings

Open the settings with Siderea → Settings… or ⌘,. They are defaults: what Siderea starts with, not what happens to the image in front of you right now.

Language

Option	Effect
System	Siderea uses your macOS language if it is translated, English otherwise.
English	The app and this help are in English.
Deutsch	The app and this help are in German.

A new language takes effect after a restart. When you change it, the settings show Takes effect after restarting Siderea. with a Restart Now button. The built-in help follows the same choice.

Appearance

Setting	Default	Effect
Color Scheme	System	System follows macOS (Light or Dark, also automatically at sunset), Light and Dark fix it. The change applies at once to every window, sheet and menu. The area behind the image stays dark in every scheme, so you judge faint nebulosity against black.
Text Size	100 %	Scales the text and the controls of the main window to 100, 115, 130 or 150 %: fonts, rows, bars, buttons, columns, tiles and the least window size grow with it. The help window and this settings window keep their size.

A new text size takes effect after a restart. When you change it, the settings show Takes effect after restarting Siderea. with a Restart Now button, as for the language. The help pages zoom with a pinch, independent of this setting. Increase Contrast in System Settings works in both color schemes.

Sheets such as Sessions and Calibration and Manage Sessions can be resized by dragging their edges; in a small sheet their content scrolls. Scroll bars follow the macOS setting Show scroll bars (System Settings → Appearance).

Display

Setting	Default	Effect
Auto-stretch new images	off	Every image you open starts with the auto-stretch of the preview switched on. Astro images are linear and look almost black without it, so switch it on if you want to see them stretched right away; the Auto pill in the image window's title bar does it per image.
Link channels	on	The auto-stretch uses one shared curve for all three color channels, which keeps the color balance. Off stretches each channel on its own. Only available while auto-stretch is on.

The Auto-Stretch item in the View menu and the Linked Channels button in the toolbar change only the current session, for the active image. The Auto pill in an image window's title bar switches that window alone. Opening the next image applies the defaults from the settings again. Neither setting changes the pixel data, the history or the export.

How the auto-stretch works: per channel (or once for all channels when they are linked) it takes the median and the median absolute deviation (MAD) of the pixel values. The MAD times 1.4826 estimates the noise σ (Hampel, 1974). The black point sits 3 σ below the median, and the midtones are chosen so that the median lands at 0.25 on screen, using the same midtones curve as Histogram Stretch.

Live preview

Setting	Default	Effect
Live preview by default	on	Modules show their result while you move a slider. The Live Preview button in the tool panel switches it for the current session. A changed default applies from the next launch of Siderea.
Preview size	2048 px	The longest side of the reduced copy the live preview works on: 1024, 2048 or 4096 px.

Smaller sizes react faster on large images, larger sizes show more detail. Apply always processes the full image, whatever the preview size.

Histogram

Logarithmic scale decides whether the histogram uses a logarithmic or a linear y-axis. The logarithmic scale is the default because the histogram of a linear astro image is one tall spike at the left. The LOG / LIN button on the histogram changes this setting too, so Siderea remembers the last scale you used.

Status bar

Show system usage (on by default) shows the CPU load and memory of Siderea, the disk space of the open project and the disk space of its linked frames in the status bar, see The status bar. Switching it off also stops measuring CPU and memory; the project and frame sizes are measured anyway.

iPhone and iPad

Mirror results to iCloud Drive (on by default) copies every finished stack, a preview and the frame report to iCloud Drive for the Siderea app on iPhone and iPad, see Siderea on iPhone and iPad. A project can also switch it off for itself in the Stack step.

Tools

Setting	Default	Effect
GraXpert	Automatic	The app that Open in GraXpert starts. Automatic looks for GraXpert*.app in /Applications and ~/Applications; Choose… picks another, Automatic goes back.
Exchange folder	Project cache or temporary folder	The folder the image is exchanged in: Siderea writes the file for GraXpert there and watches it for the result. By default cache/graxpert in the project, without a project a temporary folder.

See Open in GraXpert.