One of the frustrating aspects of narrowband imaging is the amount of exposure time necessary to get a narrowband image with blue, gold, and neutral colors, specifically the colors of the Hubble Palette (SHO). It can take many hours to acquire the exposures needed to be able to produce an image that looks good using the SHO/Hubble Palette.

What typically happens with an image that doesn’t have enough exposures is an image with a green cast to it. While there are certainly ways to achieve the Hubble/SHO color effect using masks and curves transformations on this green image, I created an easy way to convert your green narrowband image into one that comes close to a Hubble/SHO Palette image.

Here’s a sample narrowband image of NGC 6188 that has a primarily green cast to it and processed to use the Hubble Palette (SHO):

The image is good, except that it is completely green. Using my technique, you can end up with an image like this:

Note the blue, gold, brown, and neutral tones of this image. I achieved this effect using something called a lookup table, or LUT. The LUT essentially tells Photoshop or Photopea.com how to transform colors to achieve the desired effect. I created the LUT using specialized software and exported the resulting file so that you can use it on your own images.

Using the Narrowband LUT with Your Own Images

You need to start with a narrowband image that you processed in some way to produce a TIF or PNG file. For example, in PixInsight, you might use the AutoIntegrate.js script using the default options. It would be best if you ended up with a primarily green image.

Once you have the green image, open it using Photoshop CS6 or later, or Photopea.com and do the following (the following directions are for Photopea.com, but you can easily adapt them for Photoshop because the menu selections are similar):

  1. Download this ZIP file and extract the contents someplace convenient on your computer
  2. From the menu, select Layer – New Adjustment Layer – Color Lookup
  3. Next to LUTs, click the downward-pointing arrow
  4. Click the second downward-pointing arrow that comes up
  5. Select the option Load .icc .cube .look .3dl
  6. Select the file you downloaded in step 1

The screen changes and displays the image with the narrowband LUT applied. Click the eye icon next to the new layer on the right side of the screen (above the Background layer) to disable or enable the effect. You can adjust the effect’s strength by adjusting the Opacity slider to taste. You can incorporate the adjustment layer into your image by selecting Layer – Flatten Image and perform further adjustments from there.

Conclusion

In this article, you learned how to apply a LUT to an image to transform it from a primarily green narrowband image into a Hubble/SHO palette image.