Light pollution reduction
Light pollution is the main problem in astrophotography, but, as you will see below, with Nebulb it is very easy to reduce it a lot and get the night sky to be shown in the pictures as it really is.
IMPORTANT: Nebulb does not use any artificial intelligence or algorithms that make things up. What appears in the images is because the camera has captured it, because all Nebulb does is remove the light pollution while preserving the information underneath.
In order to reduce light pollution in Nebulb, the "Light Pollution" module is available (in the right tool panel):
IMPORTANT: The key to greatly reduce light pollution is to keep the image noise as low as possible (the lower the noise, the more it is possible to reduce light pollution). For this reason, Nebulb is based on image stacking, as it is the most effective technique to reduce noise and, moreover, the one that is able to extract the maximum information from the images. Or, to put it another way, stacking not only eliminates noise, but also concentrates in a single image all the good information that is scattered in the original images.
Reduction
The first step in reducing light pollution is to use the "Reduction" slider.
By means of this slider, light pollution can be reduced to the desired level (in up to 5 reduction stops). In other words, this control allows you to gradually select the desired level of reduction, from a level of 0 (light pollution remains as it is) to a level of 5 (light pollution is reduced in 5 stops).
Below are some images in which you can see the effect of the "Reduction" slider (from 0 to 5 stops):
As can be seen, the more light pollution reduction is applied, the darker the sky becomes, while the Milky Way becomes clearer and clearer as it is no longer hidden by the light that used to cover it.
And this is precisely the great advantage of Nebulb's light pollution reduction: it manages to eliminate the light gradients in the sky, preserving all the information of what lies below.
IMPORTANT 1: Light pollution reduction is effective against all types of artificial lighting (regardless of colour), as well as against moonlight.
IMPORTANT 2: The light pollution reduction is applied on the sky part of the image, not on the ground part.
Gain
Although applying light pollution reduction largely eliminates the effect of artificial light (and also moonlight), it is true that the sky can be a little dark. This is precisely what the "Gain" control is there to correct.
By adjusting the gain it is possible to increase (or decrease) the level of intensity of the sky, while respecting all the information in it. In a way, the "Gain" slider is like adjusting the exposure of the image, but during the process of light pollution reduction. The result obtained by adjusting the gain is not exactly the same as when modifying the exposure, but it is quite similar.
For this reason, it is recommended to first adjust the gain (without exceeding it to avoid that nothing is "burnt") and then, if necessary, adjust the exposure, as the "Exposure" control prevents "burnt" areas much better.
Below you can see how the image in the example above looks when increasing the gain:
Evenness
The "Evenness" slider allows you to balance the different brightness areas of the sky, i.e. it lightens the darker areas of the sky to make it more even.
As you can see in the image below, increasing the "Evenness" slider makes the highest part of the sky less dark, while at the same time respecting the brightness of the rest of the sky.
Also, the effect of this control is particularly noticeable when there is a large light imbalance in the sky (because light pollution is more intense in some areas than in others). Below you can see an example of this situation:
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