Reprocessing Old Data - Reflection in the Dark - The Iris Nebula

 A long-Overdue Update and a Fresh look at the Iris Nebula

It has been a while since my last post. The past few months have not left much time for imaging or writing, but I have still been active in the hobby - attending NEAF (Northeast Astronomy Forum), participating in astronomy outreach, and working with our club's imaging group to install and tune some new gear.

Since I don't have any data to play with, I decided to try and reprocess some old data with new tools and techniques. I chose my image of the Iris Nebula (Reflection in the Dark). The Iris Nebula is a great test subject for reprocessing because it combines bright reflection nebulosity with dim dark dust. This makes it a challenge to bring out the dark nebulosity and dust without blowing out the brighter regions. You can view the original blog post here.

The two new tools that I used in processing this image were Multiscale Gradient Correction (MSG) and Multiscale Adaptive Stretch (MAS) in PixInsight. MSG is newer tool in PixInsight that removes the gradient in the background of the image. This tool worked well for this image but is not my first choice for gradient removal as it is tedious to use. MAS is new tool for making an image non-linear (stretching). I really like this tool, it allows a lot of control and retains good color saturation. I believe the resulting image has a much cleaner background and the dark dust/nebulosity has improved contrast. 

Reprocessed Version of the image:

Reflection in the Dark - The Iris Nebula - Reprocessed in June 2026. Image originally captured in May 2023.

Before and After Slider:

Processing Details:

Linear Processing:

• Started with existing master from original processing run
• Spectrophotometric Flux Calibration (prerequisite for Multiscale Gradient Correction)
• Multiscale Gradient Correction to remove the gradient
• BlurXTerminator (Correct Only) to fix any star aberrations
• Spectrophotometric Color Calibration to color calibrate and neutralize the background
• BlurXTerminator (Full) to perform deconvolution and sharpening

Non-linear Processing:

• Multiscale Adaptive Stretch to make the image non-linear
• StarXTerminator to remove the stars

Non-linear Process - Starless Image:

• NoiseXTerminator to remove noise
• Histogram Transformation to make adjust the histogram after noise reduction
• Create HDR Script to recover detail in bright areas of the image
• NoiseXTerminator - additional noise reduction
• Curves Transformation to add Saturation
• Curves Transformation to add intensity and contrast
• Image Blend Script for sharpening
• Exponential Transformation for additional intensity and contrast

Conclusion:

It was fun to come back to older data and rework it with newer tools and techniques. This project was a good reminder that old data can still have something new to offer, especially as processing tools improve and our own skills continue to develop. Hopefully the stars align soon and I am able to collect some new data. In the meantime, stay curious and keep looking up!

Clear Skies!

Ernie