Post-processing images (examples: M42 and M51)

[AstroPhil]

Hello everyone,

I wasn’t sure whether to post this here or in the “Image processing, Help and Techniques” thread but as I class myself as relatively new to the business of imaging in general, hopefully this is a good place (if not, mods, feel free to move).

So far I’ve been having fun using a Starlight Express Ultrastar on my two Refactors (ZS71 and Tak FC100DL): even though this CCD is uncooled, it’s cheap and flexible enough to get me going (as well as doubling as a guider if I go further etc.). But I digress. Thanks to this forum and some recommended books, I’m happy with the standard processing method for lights, darks, flats, bias, dark/flat etc. And have so far used freeware (DSS) to process the images (image capture done via Nebulosity).

My question is this: once the stacking/processing is complete, there is then a myriad suite of options for tinkering with the final image. I’ve so far used the rather basic levels/stretch in DSS, as well as Photoshop (CC2017). Both seem to work okay and my image of M42 seems better with the DSS version (I think this was a Log(root) option) rather than the more expensive PS. For the M51 shot, I went with the PS processing. So, do folks have a ‘standard’ type of post-processing workflow they like, and works well in terms of making nice images? Or is is a simple case of trying all the options until it ‘looks good’? Is the key starting point the levels (say?).

Also, is there any trick to avoiding blowing out the centre of bright objects whilst still capturing fainter detail further out?

Thanks!
Phil

P.S. A bit more info for anyone interested. The images of M42 were 1 minute subs (30m total) using the ZS71; the M51 was 5 minute subs (75m total) using the Tak. Both used an 0.8 reducer. Original data here if anyone cares to tinker! https://www.dropbox.com/sh/av61hdwspfm6aan/AAApZrr3PmkOuPsgwMU74mmKa?dl=0

 

M51_adj_emb_procF.TIF

m42_adj_emb_procF.tif

[Art Gecko]

Hi Phil,

I've been doing AP for about a year or so and also class myself as a beginner, so my advice may not carry as much weight as others here on SGL... but I do feel that I can point you in the right direction, so here goes...

1: DSS is used for stacking images. Nothing else. If you use the post processing tools to look at the final image, make sure you check the box marked "embed changes but do not apply them" otherwise you will lose the colour from your images which seems to have happened in the examples above and you will find that post preocessing in proper software will be much harder if even possible at all.

2: post processing can be done in a range of software (not DSS) including Photoshop, gimp, nebulosity (which you have) pixInsight, astroArt... to name few. Learning curves vary but all will do a fine job and there are plenty of turorials around for the most popular ones like Ps and PI on here and YouTube.

3: Many people have a set "workflow" they follow as a standard path to pull the data out of their images, then make tweaks to bring out certain details... if you look around you will find links to workflows that you can follow to create a reasonable image in your preferred post processing software... personally, I like Photoshop.

4: in regards to not blowing out bright regions of your image, layers are your best friend! Stretch your image until the bright region looks ok, then duplicate the layer and stretch that to bring out the fainter stuff then add a layer mask and "paint out" the blown out areas to reveal the nicely stretched layer beneath.... works in Photoshop, other software may have different methods.

most of all, have fun while you're learning all this stuff... astrophotography has to be one of the most technically challenging hobbies to take up, so dont worry if it takes a while to get it all coming together... like I said I've been doing it a year now and still consider myself at the very bottom of the learning curve! I think you never really stop learning in this game! 

[bobro]

Hi Phil,

Greetings from just across the water!

Lovely images and nice scopes to image with!

Good advice from Art above. I thought to add a bit more about colour, but realised your CCD may be mono....

Bob