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 ƒ/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.
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.