Test of a PixInsight Toolbox Script to build a synthetic SHO image from an OSC image taken through an Altair Quadband filter.

The image was captured using AstroDMx Capture, through an Altair Starwave 60 ED refractor with an 0.8 reducer/flattener and 2" magnetic filter holder with an Altair 2" Quadband filter, and an SVBONY SV605CC OSC 14 bit CMOS camera.

The Elephant trunk nebula

RGB image

It is best to remove the stars before the nebulosity is processed. Star removal can be done in PixInsight, Gimp or Siril.

The starless RGB image was processed with a PixInsight scripts:

Scripts  ► Toolbox  ►  CreateHubblePaletteFromOSC

PixInsight with the synthetic SHO image on the left

Starless synthetic SHO image

This image doesn’t look like a typical published SHO image but it does look like many SHO images when they are first constructed. It is usual for SHO images, which are very green, to be selective colour processed to reduce the green and to introduce the familiar golden tones of the Hubble palette. PixInsight, Photoshop, Affinity Photo and other software are all able to do selective colour processing.

Synthetic SHO image loaded into Photoshop CS2 for selective colour processing

Selective colour processing in Photohop CS2 to bring out the Golden hues and the blue.

Curves processing in  Photoshop CS2

Neat Image was used to denoise the image .

Starless synthetic Hubble palette

Stars that were removed from the original image

Synthetic Hubble palette image with the stars replaced

The Wizard nebula with Altair Quadband filter data

Processed RGB image

The stars in the original RGB image were removed by starXterminator in PixInsight. However, they could have been removed by Starnet++ in PixInsight, the Gimp or Siril.

Then:

Scripts  ► Toolbox  ►  CreateHubblePaletteFromOSC

The CreateHubblePaletteFromOSC script was applied to the starless RGB image which produced a very green synthetic SHO image.

The image was saved along with the stars image, and the synthetic SHO image was denoised in Neat Image. (of course, denoising could have been done in PixInsight or other software such as the GMIC plugin in the Gimp.

Then the denoised image was loaded into PhotoShop CS2 and subject to selective colour processing to reduce the green and introduce the desired golden hues characteristic of published Hubble Palette images.

Progressive stages of selective colour processing

Final stage of selective colour processing

Curves were used to further process the synthetic SHO image.

The image was then denoised again in Neat Image.

Synthetic SHO starless image

Synthetic SHO image with stars back

In conclusion, the PixInsight Toolbo script CreateHubblePaletteFromOSC is very capable and with an OSC image produces a result that can, by selective colour processing, produce a reasonable approximation to a true SHO image. It should be noticed that the same script can produce its own version of every possible palette that can be constructed from Ha, SII and OIII data except SOH, which must be an oversight. We shall explore these in the future.