Revisiting the Rho Ophiuchi cloud complex

Several years ago I took a sequence of images of the Rho Ophiuchi cloud complex and posted the result on these pages. As noted at the time I used a Nikon D700 paired with a Nikon 85mm Ć’/1.8 lens all mounted on an iOptron Sky Tracker. Images were stacked using Deep Sky Stacker and post processing was done using Photoshop CS6 and Astronomy Tools v1.6.

Rho Ophiuchi cloud complex
Rho Ophiuchi cloud complex

Since then I have been experimenting with different tools for postprocessing astro photos. Along the way I discovered some interesting software called rnc-color-stretch from Clarkvision.com.

The rnc-color-stretch algorithm does 3 main things. 1) Analyze the image histogram to maintain a black point or use set low level color throughout the stretching process. The histogram is analyzed at multiple stages from beginning to end. 2) A power stretch while maintaining the black point. 3) Recover lost color after the stretching process. How far you can stretch an image depends on the signal-to-noise ratio.

I’ve been testing this software on both recent and older images. I thought it might be interesting to try it on the Rho Ophiuchi images taken in 2015. Once again, I used Deep Sky Stacker to register and align the images. Then I ran rnc-color-stretch. The result is the image shown above. I thnk it did a fine job of pulling out the details and the color.