NGC 1499 California Nebula in SHO

The California nebula (NGC 1499 or SH2-220) is an emission nebula in the constellation Perseus. Due to its low surface brightness, it's hard to observe visually.

As the stars are looking ugly after linear fitting of the Ha, SII and OIII channels, I decided to combine in the pre-processing all channels (L, R, G, B, Ha, SII and OIII), which are offered by telescope.live,, that all channels are aligned. The Ha, SII and OIII channels were loaded in SiriL, denoised using the GraxPert python frontend for SiriL. Deconvolution was done using the SiriL implementation and then the new AutoGBE python script for background extraction was used. The latter was very tricky, because the calibration of the SII and OIII channels isn't optimal in this dataset (maybe this can be re-visited). After all this was done the stars were removed and the channels were linear matched (linear match with stars doesn't work in SiriL). Subsequently, the new Veralux Stretching was performed.

With this processing done the image was transferred to Affinity photo, a luminance layer was generated and tone mapped to emphasize the structure of the nebula. Then the colors were optimized in order to introduce a stronger separation between the blues and the yellows. Then the stars were re-introduced. The stars were used from the SPCC calibrated RGB channels of the corresponding dataset.