When imaging using narrowband filters such as hydrogen (Ha), oxygen (OIII), and sulfur (SII) in order bring out certain more detail in nebulae, the three separate filters are combined by putting the sulfur in the red band, the hydrogen in the green band, and oxygen in the blue band hence the SHO Palette (a.k.a. the Hubble Palette).
So shortly after processing this image using the traditional SHO Palette combination I happened to watch a video by Cuiv, The Lazy Geek (
AMAZING Hubble Palette technique!) where he described a new SHO processing method developed by Steven Miller of Entering Into Space. Steve's video (
Colorized SHO Palette NO MORE FIGHTING THE GREEN!) is very comprehensive and definitely worth a watch as is Cuiv's. The basic premises of this method is to colorize the Hydrogen, Sulfur, and Oxygen prior to combining them. The benefit of doing this eliminates the oversaturated green tint that typically is produced when combined. Additionally I learned a lot of new PisInsight tricks such as making masks with the ACDNR noise reduction function.
Method SummaryData from narrowband filters is gray so it is simply combined directly into the desired channel bands. The summarized version of using this method is as follows: First do your normal linear processing on each filtered band and then change each image from gray to RGB. Second, make the images nonlinear and equalize the backgrounds - I did this using EZ Soft Stretch which automatically stretches it and equalizes the background. Third, colorize the Ha to a gold color, the OIII to a deep blue color, and the sulfur to a red-yellow color. Lastly, the images are combined using PixelMath. The color combination selection in PixInsight will not work on RGB data.
Results
My normal narrowband processing in PI consists of cropping, dynamic background extraction, BlurX, StarX, EZ Stretch. After stretching the images (making them nonlinear), each filtered image was colorized using curves and then a bit of noise reduction was done using NoiseX. Figure 1 shows the final color of sulfur, Figure 2 shows the final color of oxygen, and Figure 3 shows the final color of hydrogen.
The three separate images were then combined in PixelMath with SII in the red channel, Ha in the green channel, and OIII in the blue channel. Figure 4 shows the result of the combination. The image looked very colorful and there was very little green, however, there was a lot of magenta. To get rid of that I did an inverse SNCR. Figure 5 shows that result which is the more traditional look. Some additional processing was done in order to make the colors more vibrant and the RGB stars from the originally processed image were blended to make the final version (Figure 6).
Figure 7 is the original image processed the traditional way a few weeks ago. I did some additional processing that I learned from Steve's video to make a second version of my original image (Figure 8). Since I liked certain aspects of both methods I decided to do a blend and produced a final image
(Figure 9).
Final Thoughts
1) There is little green in the combined image , howere there may be other over bearing colors.
2) There was more nebulosity in the combined image and it seemed to be more vibrant.
3) The colors may be highly subjective depending how the colorization is done.
4) The method seems to work and hope to try it out again.
Figure 1 - Colorized Sulfur (Yellow-Red)
Figure 2 - Colorized Oxygen (Blue)
Figure 3 - Colorized Hydrogen (Gold)
Figure 4 - Combined SHO
Figure 5 - Combined SHO after inverse SNCR
Figure 6 - Colorized SHO Palette
Figure 7 - Original Hubble Palette SHO Image
Figure 8 - Original SHO Image with Entering Into Space Enhanncements
Figure 9 - Blended Image (Fig. 6 and Fig. 8)
IC 410 - Tadpoles (2023)
Dates: 12-29-22, 1-9-23, 16, 18, 24, 2-6, 8, 10, 11, 14, 15, 18
Camera: ZWO ASI1600MM-Pro
Telescope: Astro-Tech AT115EDT 115mm Refractor Telescope
Barlow: None
Focal Length: 805mm (644mm w/ FR)
f/7
Focal Reducer: 0.8x AstroTech Field Flatterner/Focal Reducer
Mount: Orion Sirius
Filter Wheel: ZWO
EFW 8 x 1.25"
Filter: Antlia Ha, OIII; ZWO R, G, B, SII
Focuser: ZWO EAF
Autoguiding: ASI120 Mini attached to an Agena 50mm Guide Scope/ZWO 60mm Guidescope
Exposure: Ha 101 x 300, OIII 94 x 300, SII 77 x 300, R 30 x 60, G 29 x 60, B 37 x 60
Gain: 139
Offset 20
Sensor Temp: -20 C
Processing: NINA, PixInsight, Photoshop, BlurXTerminator, StarXTerminator, NoiseXTerminator, Bill Blanshan Masks.
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