If you take a lot of astrophotography, you know all about gradients. They are almost always present in your images and they must be removed to smooth the sky background and make your image look its best.
Color gradations are caused by light pollution, bad flat frames that haven’t cleaned up your optics, dark corners, and even natural gradations that appear in the night sky.
There are already some good software based solutions for gradient removal, such as the DBE and ABE tools in PixInsight, a paid image editor. There are also some great plug-ins for Photoshop and Related Photos from RC astronaut, It’s amazing. I use them all the time.
Now, many night photographers are praising this free, open source software called GraXpert. In my review, it works well as paid options and as a bonus, gives you the option to save the stretched version automatically, which will save the imager time and effort .
This is an example of the galaxies M65 and M66. I loaded the file in FITS format, but you can load a TIFF file or even a JPEG file. It is recommended that you use the best image formats for dynamic range, which will result in JPEG not being as expected.
Here is the image before any gradient work:
You can see the uneven red of the background on the left and it’s even more obvious on the right side of the image.
You press the “Generate Grid” button on the app and this will appear:
The software will try to place markers or what it calls sample points where the background sky is. It avoids galaxies and stars. It’s just looking for the sky background. Those markers can be removed with a single click or dragged to another location. I noticed the software missed some areas on the top right and needed some more on the leftmost edge, so I added them. If the sample point appears in a part of a nebula or part of a galaxy, simply move or delete the point.
Then when you’re satisfied you hit the “Calculate Background” button and your gradient will be nicely scaled down.
It did a great job on this image, although there is still a red streak on the left.
I’ve tried GraXpert on a number of images and get good results each time. I’m also happy to see the software in development. You now have the option to save the image that GraXpert has created in a stretched format. I still have some work to do in Photoshop to get the image just right, but auto-stretch is a useful and time-saving feature.
This is an image I processed of the Veil Nebula. GraXpert reduced some nasty gradations in the original, then I did some star reduction and color balance in Photoshop.
As I said above, GraXpert isn’t the only software that can delete astrophotography, but it’s free and works pretty well. It works on Windows, Mac and Linux. It is not a plugin, but a standalone application. There are video tutorials and PDF manuals and the software is easy to use.
It is not a complete editing solution. Once you clean up the color bands, you’ll want to be in a different editor for color balance, noise reduction, sharpening, or whatever else your image needs.
It is available on GraXpert websiteand I would like to know your impressions.
