Sadr edditing problem

Well obviously, the color balance is way off. I don’t use PI but In general, to get a starting color balance, assuming the three narrowband images are of similar density my workflow would be:

Correct gradients

LRGB recombination with alignment and linear matching

Plate solve

SPCC color calibration

This should get you close unless one of the frames is really out to lunch. In that case you can try pixel math instead. None of that will get you good star color though. SetiAstro has a great plug-in for that if you didn’t get RGB data.

After that it should be:

Sharpening

Noise reduction

Star removal

Stretching both the starless and star only plates

Final touch up of both plates and recombination (I usually use Affinty Photo as it gives me much finer control)

How are you assigning the channels? I know you are working from SHO data, is that the palette also? Have you tried others like Forax?

Tony Gondola · Aug 19, 2025, 08:11 PM

How are you assigning the channels? I know you are working from SHO data, is that the palette also? Have you tried others like Forax?

Standard way of assigning the channels

R - Sii

G - Ha

B - Oiii

My default workflow is to do linear fit and combine them in pixelmath. Usually Ha is quite dominant but in most cases I can create a good color composition via a reduction either with the curve tool or SCNR, but not on this target. I haven't tried fornax, I prefer the Hubble palette.

First of all, you need to correct the gradients in the image. There was a slight bottom right → top left gradient in all channels, I lazily fixed it with MARS. The lack of reference Sii data was inconvenient, but it should be doable still. Getting rid of gradients before color calibration is crucial, as they can skew the colors by quite a lot.

If you want to do a three-channel color composite of narrowband data, like SHO, linear fit is not a good nor reliable option to achieve good color balance. Neither are SPCC and PCC for that matter, as they’re not designed to create a good balance between narrowband channels but rather one that represents the relative intensities, which will pretty much always make Ha dominate over other emission bands. The way to do it right would be the Color Calibration process:

Start with making a background preview, somewhere where there’s minimal or no signal in any of the channels. In this image, the long dust lane in the middle is a good fit. Use Background Neutralization with that preview as the background reference. Then, in Color Calibration, select the same preview as a background reference. Then deselect Structure Detection and select Manual White Balance and play around with the sliders until you like the result. Optionally, if your color balance is off at the beginning, you can select a bright feature visible in all bands as a white reference and run Color Calibration with Structure Detection disabled to get an initial color balance.

People often massacre the green with SCNR when doing SHO - I believe this to be a mistake. To me, it’s basically throwing out 1/3rd of the data. Suppressing green itself is fine, in the end it’s up to personal preference, but there are other, better ways to achieve that: Color Calibration, Histogram Transformation, Curves. They all can make the image less green-dominant while preserving the delicate color gradients between yellow/orange and blue and the extra layer of color depth. If you are going to use SCNR, do it at a low strength and be careful not to lose the color depth, but if doing a serious edit I recommend giving other methods a shot.

Either way, if you don’t particularly like SHO here, I recommend exploring other color palettes, especially dynamic ones similar to Foraxx’s. Or trying out channel mixing/blending. Both give you much more room for creativity in my opinion.

Here’s what I came up with. Processing: MGC → Background Neutralization → Color Calibration → slight denoise in Sii and Oiii → StarX → Invert → SCNR @ 20% → Stretch → 2x Dowsample (for the Magma image, SCNR was skipped)
1. Normal SHO
2. Dynamic ‘Magma’ palette with a slight saturation boost. The pixel math for the palette was made by Uri Darom, you can probably find it online somewhere.
📷 SHO.jpg📷 Dynamic 'Magma'.jpg