Preparing Images for Starry Landscape Stacker
Typically, for each shot, you will have 10 or more exposures. You might also have a set of dark frames. Load your images, both your light frames and the corresponding dark frames, into the raw converter you prefer to use (e.g., Adobe Camera Raw, Lightroom, Aperture). Now you want to make some basic adjustments. I think the most useful adjustments are as follows:
reduce the contrast dramatically—I often set the contrast as low as it will go and increasing the brightness to compensate for shooting at a lower ISO setting. It is best to have the dark areas brighter than you want them to be in the final image. This will improve the alignment of dim stars. I also try to avoid making the bright stars so bright that they lose their color. You will darken the dark areas and make other tone adjustments after you have processed the images with Starry Landscape Stacker.
turn off sharpening and noise reduction—In Lightroom this is under "Detail". Applying sharpening or noise reduction to the original images before processing with Starry Landscape Stacker will reduce the quality of the final result.
apply lens chromatic aberration corrections
apply vignetting correction only if you are not using flat-field frames—using flat-field frames is more work but can give a better result.
Your goal at this point is to correct for lens errors and adjust the tonal range of the images so that not too many stars are blown out and the darker areas are a bit brighter than you want them in the final image, and nothing more. Be sure that identical changes are applied to all images—both the light frames and the dark frames. Pay particular attention to white balance. For example, in Lightroom, if the white balance is set to “automatic” and you “sync” the settings across all the images, the “automatic” setting is copied, not the specific temperature and tint. This means that the color balance is not synced. I always leave my camera in auto white balance and in Lightroom change white balance to "Custom" in the image that I am using as the master for syncing.
Once you have these basic corrections synced across all the images, you can go through the individual images and make adjustments to specific images. Mostly this means painting out any stray light from cars or flashlights in your images. There is no need to paint out anything that appears at a specific place in only one image like an airplane track. Airplanes (and sometimes cars and flashlights) appear in a different place in each image. Starry Landscape Stacker will remove these things as part of its processing. If you have something that sits in one place for several (but not all) frames, it is best to paint it out. Starry Landscape Stacker will make any errors in your painting less visible as part of the noise reduction process.
When you are done, export your images as 16-bit tiff files. Often the default is 8-bits, so be sure to change this. It is important that the exported files have 16-bits of data as Starry Landscape Stacker needs all the details it can get in the dark areas.
Most image processing tools allow saving of transparency data. For example, Lightroom has a checkbox labelled "Save Transparency" in the "File Settings" pane. It is important to not save transparency as this will confuse Starry Landscape Stacker. Most image processing tools default to not saving transparency.
When saving images for processing with Starry Landscape Stacker it is best to include all metadata in the images. Starry Landscape Stacker will copy this information into the files it writes which will make final processing and digital asset management more convenient than it would be if the metadata is stripped. Also, Starry Landscape Stacker uses the image capture time, lens information, and sensor information to improve alignment of the sky.
Starry Landscape Stacker can work with pre-built masks rather than generating its own. You can construct a mask image with any image processing tool (e.g., Photoshop, Pixelmator, Affinity Photo) and supply the mask to Starry Landscape Stacker along with the light frames and dark frames. The mask image must have the same pixel dimensions as the other frames and a non-zero value for sky and 0 for ground.
Once you have your 16-bit tiff files you can process them Processing Images with Starry Landscape Stacker.