Reduction of chromatic aberration
Within the "Preprocess" module you also have a utility to reduce the chromatic aberration of the image before stacking.
In Nebulb the chromatic aberration reduction is made based on an estimation made directly on the image itself (no preset value is used for each lens). Because of this, the chromatic aberration reduction may vary for different images captured with the same lens (depending on how the effect of chromatic aberration is seen in the image). And, for this reason, it is also possible to apply chromatic aberration correction to any lens, even if the lens metadata is not saved in the image file.
As with luminance noise reduction, chromatic aberration reduction is performed directly on the original RAW image (before demosaicing to obtain the color image on Bayer filter sensors (the vast majority)).
ATTENTION: Chromatic aberration reduction is available when importing RAW images from Bayer sensors. That is, chromatic aberration reduction cannot be used when importing images in TIFF or JPEG format and also when importing RAW images from Fuji cameras (the sensor these cameras have (X-Trans) is different from the rest of cameras with Bayer filter). In these cases, the chromatic aberration reduction option is disabled and cannot be selected.
Here are a couple of examples where you can see the correction you can achieve with Nebulb chromatic aberration reduction:
Cropping (at 200% zoom) of a corner of an image with chromatic aberration | Result of chromatic aberration reduction |
Cropping (at 200% zoom) of a corner of an image with slight chromatic aberration | Result of chromatic aberration reduction |
IMPORTANT: It is not recommended to perform any lens correction (especially distortion correction) in another software before importing the images into Nebulb, as such corrections may negatively affect the stacking. Note that during stacking, lens distortions have to be corrected (implicitly) in order to align the stars accurately, so if the images have been previously modified with another correction this may cause strange artifacts to appear in the resulting stacked image. Therefore, in case you want to correct the image distortion, I recommend that you do it on the final image obtained from Nebulb.
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