Recently I’ve been seeking a way to improve the way I remove light pollution from my astrophotography images. In this post I am going to compare several different techniques for doing this and try to decide which is the best. So, if you want to improve your astrophotos read on!
I will compare the following:
Gradient Xterminator
Graxpert
Manual methods to reduce light pollution in Photoshop
Two kinds of images
The first kind of image that I need to remove light pollution gradients from consists of a smaller depp sky object and a large area of sky which needs to have the light pollution reduced. This is quite an easy image to handle as it is easy to extract the background gradient or skyglow and leave the nebula/ galaxy alone.
The second type of astro image is when there is nebulosity covering large areas throughout the image making it more difficult to remove without affecting the details of the object we want to enhance. This is the type that I am currently seeking an effective solution for. Up to now I have been using background extraction in Siril with varying success.
When to apply light pollution and gradient removal
There are two possible points in your astrophotgraphy post-processing workflow when you might want to remove any light pollution or gradients you see. The most effective, according to many, is to remove gradients from your linear image. In other words, before you stretch your image. The reason for doing this is to prevent stretching from making the gradient or haze from light pollution worse and therefore harder to manage.
The second point is later during your editing workflow when you have already stretched the image maybe several times but then found there is still some light pollution that needs to be reduced.
I wanted to compare the different methods that I know of and the tools I have access to in order to figure out which are the best and when I should consider changing how I remove any light pollution in my images. Should I use different methods depending on the image or always the same one?
When removing light pollution from a linear image we will need to stretch the image only to view the gradient in order to remove it but the stretch should not be applied to the image once it is saved. Fortunately many tools, such as Siril or Graxpert, for example, allow us to apply a temporary stretch like this.
I will also need to be careful to apply the exact same stretch to all my images to check the effectiveness of the different programs. This means that my images should be matched as close as possible for editing.
Two types of light pollution removal tools
There are tools that are simply pretty much one click tools and other methods that will need us to follow a few steps such as those that are carried out in photoshop manually. If a one-click tool works best then why do it manually? Let’s see if this holds true.
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