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wavelet transformations of the sky background modeling

From the extraction of the bottom of a deep sky image we can correct the problems non-uniform illumination and color, such as those associated with vignetting. This forms part of own calibration of the image, and ideally should be applied on raw data linear.

PixInsight has two processing modules extraction mechanisms and automatic dynamic background:

• AutomaticBackgroundExtraction (ABE)
  
• DynamicBackgroundExtraction (DBE)
  

In normal situations ABE get an excellent modeling of the background of the image, while DBE is more flexible and appropriate when faced with more complicated cases, especially when there is much to refine over the procedure, and the user can intervene dynamically over the image.

Depending on the nature of the problem in different lighting and / or color, image correction must be made by subtraction or division. The vignetting for example is a multiplier effect, so the division is more appropriate. On the other hand, light pollution and atmospheric extinction are additive effects, so that should be neutralized by subtracting.

This is a case of vignetting easy to correct with ABE by division. I have used most of the parameters included by default, except under the generation and global decline of samples, thus avoiding some of the boxes are included on the photographed object.

Figure 1 .- Original vignetting

Figure 2 .- Distribution of samples in ABE

Figure 3 .- Extraction Automatic background (pseudo-flat)

Figure 4 .- Correction to ABE by division

DBE is instead appropriate in more complex cases, as this wide-field photography affected by atmospheric extinction and light pollution. In this test uses only the default, which already introduce a significant improvement.

Being able to act dynamically on the image allows the user to manually place the samples on the bottom of the sky and forcing the modeling mechanism in difficult situations, such as gradients themselves Milky Way.