Advanced settings for light pollution reduction

Advanced light pollution estimation

Nebulb first has to estimate the light pollution before it can reduce it, for which it uses default parameters that are optimal for most situations.

However, there are particularly difficult occasions (due to the existence of specific and intense sources of light pollution) in which these optimal parameters may not be the most appropriate, as they do not obtain the best possible estimate of light pollution.

Because of this, in some cases uneven areas may appear in the sky when applying light pollution reduction, as can be seen on the right-hand side of the sky in the following image:

Result of reducing light pollution 5 stops using the optimal estimation method

To solve these more complicated situations Nebulb has an advanced method for light pollution estimation.

Thus, selecting the "Advanced" method enables the "Density" and "Adaptability" controls, by means of which it is possible to adjust the light pollution estimation more precisely.

Density: This slider sets the number of points on the sky that Nebulb uses to estimate light pollution. A higher density can help Nebulb to better adapt to situations where light pollution changes considerably from one area of the image to another.

Adaptability: This slider regulates Nebulb's ability to adapt to variations in light pollution in the image. Thus, high values (above 3) can give better results in images where the light pollution is not uniform (some areas are very bright and others much less). On the other hand, low values (below 3) may work better on images where light pollution is fairly uniform. Also, in general, "Adaptability" values between 2 and 4 are usually adequate for the vast majority of cases.

IMPORTANT 1: The light pollution reduction adjustments are non-destructive (like all Nebulb adjustments), so you can test as much as you want and get the result you like.

IMPORTANT 2: In most cases the "Optimal" method usually gives the best results, but at any time you can also try the advanced settings.

IMPORTANT 3: In the case of using the "Advanced" method it is usually more effective to adjust the "Adaptability" than the "Density", so it is always better to try the "Adaptability" slider first.

Very irregular light pollution situations

In cases where light pollution is very irregular, or there are areas where it is much more intense than in others, it may be interesting to try the advanced settings so that Nebulb adapts better to the existing light pollution.

Here is an example where increasing the "Adaptability" a little bit gives a better result:

Result of reducing light pollution 5 stops using the optimal estimation method (the right part of the image shows some unnatural light irregularity)

Result of reducing light pollution by 5 stops, using the advanced estimation method and increasing the adaptability to 4 (in this case the right part of the image looks much more regular and natural)

Uniform light pollution situations

On other occasions (especially when using medium or long focal lengths) it may happen that the light pollution in the sky is very uniform. Well, as you can see in the following example, in these cases you may obtain better results with lower "Adaptability" values.

Image of the constellation Orion in which the light pollution in the image is very uniform

Result obtained by reducing the light pollution by 5 stops using the optimal method. The result is better than the original, but non-uniform areas around the Orion nebula appear

By applying the advanced method and reducing the adaptivity to 1, the nebulae around Orion are much more prominent and the overall uniformity of the image is also very good

Effect of setting inappropriate estimation adjustments

In general, adjustments are considered good when the sky, after applying the light pollution reduction, is uniform and natural (nothing unusual is observed).

However, if the sky is uneven (with light and dark areas where it should not be), it means that the light pollution estimation adjustment has not been the most appropriate.

Thus, here is an example of the difference between good settings and inadequate settings:

Image obtained after stacking (without any light pollution reduction)

Image resulting from applying light pollution reduction with the optimal method. In this case the result is very good because all the nebulae in the galactic centre of the Milky Way are perfectly visible, without any irregularities appearing in the sky

In contrast to the previous image, in this case there are strange light irregularities both above the horizon and in the upper right corner (due to a too low "Adaptability" value)

In this case the sky is perfectly uniform, but the problem is that the nebulae of the Milky Way appear too clipped (due to an over-adaptation in the estimation of light pollution by having set too high a value of "Adaptability")