Swansea Astronomical Society Blog

You may have noticed that in posts such as Anne Startup's recent post of the Spider nebula, she mentions removing stars from the image, doing some processing of the starless image and then replacing the stars.

There are a number of ways of doing this and reasons for doing it. The resulting final image will not be overwhelmed by the stars and the stars will not be bloated.

I have produced an animation of a processing of our Pelican nebula image to illustrate these points.

The images in the animation are as follows:

• Original image stretched enough to show the stars.
• Image with stars removed.
• The removed stars in a star mask.
• Image with stars removed.
• Image with stars removed stretched to reveal the nebulosity.
• Stars from the star mask placed back in the stretched nebulosity image.
• What the original image looks like if simply stretched, causing some star bloating and overwhelming the image with stars.

Click on the animation to get a closer view

Animation of the above images

It is, of course, not essential to preform processes such as this. It is the personal preference of the person processing the images. The decision to do this will depend to an extent on the density of stars in the image and to what extent they overwhelm the visibility of the nebulosity. Not all images will benefit from the process, but some certainly will.

Various software packages are able to remove stars with various degrees of success. The program used here is a neural net program called Starnet++v2 and is the same program used by Anne in her Spider nebula post.

Steve Wainwright

posted by astroimager  # 2:19 PM 0 Comments

 Click on an image to get a closer view

2 pane white light mosaic using the Baader Herschel Wedge and Jim's Ascent 80mm, the camera was a Hypercam 178 

Best 20% of 2000 frames using my Hypercam 174 and the Quark fitted on an Altair Ascent 80mm, f/7 refractor. I sharpened and stretched them in IMPPG. Finished in Photoshop CS3.

H-alpha images

posted by astroimager  # 6:45 PM 0 Comments

I was using my 8” Richie Cretian f/8 and the ultra star camera as a digital eyepiece.

Click on an image to get a closer view

posted by astroimager  # 6:32 PM 0 Comments

My third image from Portugal, IC4l7.

A combination of narrowband nebula with RGB stars added at the end. 8 hours exposure using the Atik428, Altair 70edt refractor and the Ioptron IEQ30pro mount.

After integration using Pixinsight's WBPP script which also crops the images, I removed the stars using Starnet2. The star image had the saturation increased slightly. I then permanently stretched the starless nebula, performed HDR and noise reduction. I ran SNCR to reduce the green and obtain the blue/gold Hubble palatte before using pixelmath to re'introduce the RGB stars for a more natural look.

I then used Photoshop CS3 to adjust the colouring to bring out the Oiii contribution in the blue sections of the nebulae.

Click on the image to get a closer view

The Spider nebula IC417 Hubble palette

Anne Startup

posted by astroimager  # 1:53 PM 0 Comments

A blend of stacked images captured with an f/5, 130mm Newtonian and coma corrector with an SV405CC OSC camera an an LeNhance filter, and an f/6, 60mm ED refractor and Field flattener with and SV605CC OSC camera and a UV/IR cut filter. The images were blended using Picture Window Pro 2.5 and post processed in the Gimp 2.10. 

Click on the image to get a closer view

The Orion and Running Man nebulae

Steve Wainwright

posted by astroimager  # 4:10 PM 0 Comments

Here's my second image from Portugal, IC1396, the Elephant's Trunk nebula, two versions.

Total imaging time 6 hours using my Atik 428 ccd, Altair 70edt refractor on the Ioptron IEQ30pro mount.

RGB filters using 5 minute subs and Ha, Oiii and Sii filters using 15 minute subs.

Click on an image to get a closer view.

Image 1

RGB stacked subs combined and colour calibrated in Pixinsight. I then used a narrowband combination script to add Ha to the red channel, Sii to the green channel and Oiii to the blue channel. I then permanently stretched the resulting image, used Starnet++2 to remove the stars and then stretched the starless image further. After processing the nebula and removing noise, I increased the saturation of the star image and then recombined them using pixelmath. I then used the star image as a mask for further noise reduction and slight star reduction.

Image 2

This time I combined the narrowband images using the Hubble palette then lightly stretched the image before removing the stars as above. I then reduced the green in the nebula image to create the blue and gold Hubble palate, did some noise reduction as above, then used the stars from the RGB stacked subs to add the stars with pixelmath. This gives more natural looking stars in a narrowband image.

Both images were then opened in Photoshop and had selective colour applied to bring out various areas in them.

Anne Startup

posted by astroimager  # 5:48 PM 0 Comments

I was using my 8” Richie Cretian f/8 and the ultra star camera as a digital eyepiece.

Click on an image to get a closer view

Jim Startup

posted by astroimager  # 2:43 PM 0 Comments

Here is my first processed image taken in Portugal. 4 and a half hours exposure using Ha, luminance and RGB subs. All taken with the Atik 428 mono ccd, Altair 70edt refractor on my Ioptron IEQ30pro mount.

Stacked and calibrated using Astropixelprocessor, Ha added to the red channel of the lrgb image, then background neutralised before removing the stars using Starnet++2.

The star Navi was removed quite well but glare was still present due to the high humidity when I was collecting the colour subs. I cloned this out before permanently stretching the image. The image with just the stars was also stretched but very gently to keep them  smaller. After some colour balancing of the nebula, I returned the stars using pixelmath.

Click on the image to get a closer view

IC59 and IC63

Anne Startup

posted by astroimager  # 12:27 PM 0 Comments

When imaging efforts are frustrated by bad weather such as we are having this week, with torrential rain to dampen your spirits; this is the time to revisit your data from earlier imaging sessions and to re-process them to see if there is any more information to be squeezed out of the images you captured.

Here is a re-processing of our image of M29, the Cooling tower cluster in Cygnus with a view to revealing the surrounding nebulosity.

Click on the image to get a closer view

M29 and surrounding nebulosity

Steve Wainwright

posted by astroimager  # 10:56 PM 0 Comments

This image was the result of stacking in Deep Sky Stacker but processing in the Gimp and Neat Image.

Click on the image to get a closer view

M45 The Pleiades

Steve Wainwright and Nicola Mackin

posted by astroimager  # 2:52 PM 0 Comments

Andromeda galaxy. Settings were 1min and ISO3200 and 350 images. I was using a 1300D DLSR Canon camera mounted on a Skywatcher 72ED APO refactor telescope with a field flattener. The telescope was mounted on a Skywatcher EQ5 tracking mount. I used a Bantinov mask and a intervalometer attached to the camera. The image was a stack of 350 images stacked in DSS and processed in the GIMP. 

Click on the image to get a closer view

M31 Andromeda Galaxy

Chris Playle

posted by astroimager  # 12:05 AM 0 Comments