Darktable losing wanted night sky detail when exporting to JPEG

Question

I took some night sky photos and messed around a bit in Darktable (Windows) to make the stars pop. The problem is that the exported JPEG dulls out the stars, even though I am exporting at 100% quality.

Taking a screenshot (windows+print screen) of the raw image in Darktable looks like the following:

However, the exported a JPEG from Darktable looks like this:

Any advice on how I can preserve the bright dots when exporting?

Edit: Asked by user to save an PNG. I saved to PNG with 8bit and compression set to 0:

Answer 1

Preview and exported images look different because the demosaicking and interpolation algorithms used are different. Even when viewing the exported image at reduced magnification, the down-sampling algorithms are likely different (nearest neighbor vs bicubic vs cubic vs lanczos). Bicubic and cubic will tend to look softer.

Consider adding a final sharpening step after any additional post processing you plan to do. If you intend no further processing, you can add additional sharpening from within darktable.

Answer 2

Per this thread, this effect could be because of the way the Profiled Denoise module:

The “profiled denoise” module and the way how the image preview is generated. To make it fast the preview only takes “part” of the image. IRC in the full image view, the image is not even demosaic? Once you zoom in a bit you will notice, that it gets unsharp like the export.

To tweak the denoising I always use the 100% view. The default settings of profiled denoise are too “strong” most of the time. So you need to change the values. I use the approach described in the manual with the two different modes and blending. And for demosaicing I switch to “VNG”
_{-- Christian Kanzian}

This may or may not be your problem, (the OP of that thread had a different problem that might or might not have gotten fixed), but it's worth a try.