How to reduce light pollution in a single image
Nebulb is a software based on image stacking, which is the most effective technique to achieve noise reduction to levels that are not possible in any other way.
However, in Nebulb it is also possible to apply light pollution reduction on a single image, although, obviously, the level of reduction that can be achieved is lower than when stacking multiple images (mainly due to the noise level).
As you will see below, the process is practically identical to the one followed by stacking images, except for the way of launching the processing. For this reason, this article focuses specifically on the particularities related to working with a single image, and for all common aspects direct reference is made to the article "How to stack images to greatly reduce light pollution".
1. Import the image
The first thing to do is to import the image you want to process, for which you can use the image import button or directly drag and drop the image onto Nebulb.
When importing the image it will be shown on the display.
2. Define the sky mask
The second step is always to define the sky mask so that Nebulb knows where the stars are in the image.
By clicking on the star button in the upper toolbar you activate the editing of the sky mask and then, using the different brushes, you can define it on the image.
For more information you can read these other articles:
3. Apply noise reduction
Since when processing a single image you cannot take advantage of the high noise reduction offered by stacking, in this case it may be especially interesting to apply the noise reduction available in the "Preprocess" module (in the left tool panel).
You can apply both luminance noise reduction and color noise reduction (in case there are also hot pixels in the image).
As you can see in the image above, for this example I have only applied luminance noise reduction because the image has no hot pixels.
4. Image processing
Next you must tell Nebulb to process this individual image in order to apply the light pollution reduction on it, for which you simply click on the following button (within the "Stack" module):
5. Apply light pollution reduction
At the end of the image processing nothing will have changed (to the naked eye), except that the post-processing modules in the right tool panel will have been enabled and you will be able to use them.
ATTENTION: The "Flying Objects" module is never enabled when processing a single image, because, in order to detect flying objects (meteors, planes, satellites...) Nebulb needs more than 1 image.
Therefore, you can now use the "Light Pollution" module to reduce the light pollution in the image you have imported into Nebulb.
You can find more information about this in this other article: "How to stack images to greatly reduce light pollution".
6. Apply image development settings
The next step is to develop the image, for which you have the "Develop" module.
The most special feature of developing in Nebulb is that, by means of the 3 buttons at the top of this module, it is possible to set adjustments to be applied to different parts of the image: on the whole image (left button), on the ground part (central button) or on the sky part (right button).
Below are the development parameters that I have applied for this image:
7. Improve the sky
In Nebulb you also have a module with specific processes to improve the sky (star reduction, star glow and noise reduction).
Below, you can see how I have applied some star reduction and noise reduction on the sky to improve this part of the image:
8. Sky/ground blending
The last step is to adjust the blending between the ground part and the sky part, for which you have the "Blend" module.
And these are the settings I have set to adjust the sky/ground transition in this example image:
Here you can also see the comparison between the original image and the one I have been able to obtain by processing in Nebulb:
Original image | Final image processed in Nebulb |
You can find more information about this in this other article: "How to stack images to greatly reduce light pollution".
9. Export the final image
Finally, the only thing left to do is to export the processed image, for which you can use the "Export Images" module at the bottom of the left tools panel.
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