Compositing narrowband images

Narrowband astrophotography uses astronomical filters to capture images of light from specific wavelength bands. It is often used to produce images of nebulae. A dedicated astronomy camera tends to be used.

The resulting frames are monochromatic but can be processed by the Astrophotography Stack Persona just like full-color frames.

Several mono images, each taken with a different filter, can be manually composited into a full-color image.

The most commonly used filters detect Hydrogen-alpha (Ha), Oxygen-III (O-III) and Sulfur-II (SII).

A composited full-color image

An example of composited, full-color narrowband astrophotography.

Before compositing, use the Astrophotography Stack Persona to create three separate images, each from a different astronomical filter's frames.

To ensure you start with a document of the correct properties, including resolution and color format, use one of your already-stacked monochromatic documents as the base on which to perform the following procedure.

  1. Copy and paste a flattened version of each of the other two mono images onto a separate pixel layer in the new document.
  2. For each pixel layer in turn:
    1. Select Layer>New Adjustment Layer>Recolor.
    2. Clip the adjustment layer to the pixel layer. (See Layer Clipping.)
    3. Set the adjustment layer's hue uniquely to red (0°), green (120°) or blue (240°).
  3. Set each pixel layer's blend mode to Add.
  4. Perform additional post-processing work as necessary

There is no universally accepted color assignment for each chemical element, so experiment. For example, the Hubble palette assigns red to S-II, green to Ha, and blue to O-III.

Use your artistic judgment in post-processing. For example, you might:

An example of the Layers panel after post-processing is applied

After compositing, use additional features help to refine the result.