PhotoDemon; free, open source Photo editing software

Every so often I come across some software that, as far as I am concerned, has been hiding in plain sight. Such a program is PhotoDemon.

PhotoDemon is developed by Tanner Helland.

It was first released in 2012. It is open source and freeware, although donations can be made to the project. At the time of writing PhotoDemon is on version 2025.4.

PhotoDemon is not installed, it is an executable along with its required dependencies and requires no administrator privileges. Aside from a temporary folder – which you can specify in the Tools > Options menu – PhotoDemon leaves no trace on the hard drive. PhotoDemon can be run  from a USB stick or SD card.

It is lightweight, fast, completely portable and works with 8 bit, 16 bit and 32 bit images; unlike many photo editing programs which reduce higher bit depth images to 8 bits before they can be used.

Due to its portable nature, PhotoDemon is only available as a 32-bit application. This means it cannot load or save images larger than  about 2 GB in size.

Complex editing actions can be recorded as macros. A built-in batch processor lets you apply macros to entire folders of images. 32 bit 8bf plugins can be installed and used. The 32 bit 8bf, Hasta La Vista, Green, HLVG, from DeepSkyColours installs and works perfectly in PhotoDemon.

PhotoDemon is very intuitive and usable. Small touches like real-time effect previews, save/load presets on all tools, unlimited Undo/Redo, customizable hotkeys, mouse wheel and X-button support, and descriptive icons make it fast and easy to use. For those who know something about Photoshop, many of the keyboard shortcuts work the same way.

PhotoDemon has very extensive file format support, including Adobe Photoshop (PSD), Corel PaintShop Pro (PSP), GIMP (XCF), and major camera RAW formats, but at the time of writing, does not support the Fits file format.

Advanced multi-layer support, including editable text layers and non-destructive layer modifications

Colour-managed workflow includes support for embedded ICC profiles.

Its on-canvas tools include digital paintbrushes, clone and pattern brushes, advanced selection tools, interactive gradients, and more.

Adjustment tools include levels, curves, HDR, shadow/highlight recovery, white balance, and many more.

Filters and effects include perspective correction, edge enhancement, noise removal, content-aware fill called ‘Heal selected area’, and resize, unsharp masking, gradient and palette mapping, and many more. More than 200 tools are provided in the current build.

Screenshot of PhotoDemon using Curves on a Star layer that has been Screen blended with the starless layer.

Screenshot showing the adjusted stars layer

PhotoDemon is right up there with Photoshop, Gimp and Affinity Photo. It will be one of the tools in my workflow for processing astronomical images. I can recommend it to any astrophotographer who wishes to use a powerful yet intuitive program to contribute to the processing of her/his images.

I was unable to get it to work in Wine in Fedora or Ubuntu Linux. If it can be made to work in Wine a special Wine ‘bottle’ may have to be developed.

PhotoDemon can be downloaded from https://photodemon.org/

The Lobster claw nebula region

AstroDMx Capture was used with an SV605CC OSC colour CMOS camera and an Altair Starwave ASCENT 60ED doublet refractor with 0.8 reducer/flattener and a Pegasus Focuscube v2. An Altair 2” magnetic filter holder version 2 containing an Altair quadband filter was placed in the optical train.

The equipment was mounted on a Celestron AVX GOTO mount. An SVBONY SV165 guide-scope fitted with a QHY-5II-M guide camera was mounted on the imaging scope. An INDI server was running on the imaging Linux computer indoors. The guide camera was connected by USB to another Linux computer indoors running PHD2 autoguiding software via the INDI server. The mount and the focuser were controlled by AstroDMx Capture via the INDI server.

AstroDMx Capture slewed the scope to the star Altair and plate-solved to centre it. A Bahtinov mask was used to enable Altair to be brought into sharp focus.

Screenshot of PHD2 autoguiding

Then AstroDMx Capture plate-solved and sent the scope to the star HD 240247. This star was chosen so that the image would frame a region containing five objects: SH2-157, the Lobster claw nebula, NGC 7635, the Bubble nebula, NGC 7538 (emission nebula), NGC 7510 and M52 (open clusters).

AstroDMx Capture was used to capture 26 x 5-minute RAW exposures of the region.

Screenshot of AstroDMx Capture saving RAW FITS files. Live stacking was used to improve the preview of the captured image.

Negative preview

26 light frames, 5 dark frames, 50 bias frames, 50 flatfields and 50 dark flats. To capture the flats and other calibration frames, the scope was slewed to ther zenith and tracking stopped. The flats were captured using a device designed to avoid lateral light leakage and using a stack of 3mm thick acrylic white A5 sheets to evenly diffuse the light from a light panel and attenuate it sufficiently to get Flats of 1.5s duration.

The Flat field equipment

The data were calibrated, debayered, stacked and part processed in PixInsight and completed in GraXpert, Seti Astro Suite Pro Cosmic Clarity and Gimp. A Pixinsight Cosmic Photons script was used to Generate a Hertzprung Russel diagram of the stars in the image.

Hertzprung Russel diagram of the stars in the stacked image

The Lobster claw nebula region. All images with RGB stars.

RGB channels linked

RGB blend of linked and unlinked channels

Annotated image

HOO rendering

Hubble palette rendering

Classical SHO rendering

Meanwhile Nicola's mammoth refactoring of AstroDMx Capture is progressing nicely, although with the decision to make a number of functional and efficiency changes in addition to making the software Wayland compliant with Qt6, the process has taken longer than was initially anticipated. The ground is being prepared for the introduction of new frameworks such as Alpaca as well as new functionality.