M31 - Overstretching - me?!

[PhotoGav]

Hi folks,

I've been fiddling around with this for the last while and seem to have hit a brick wall... here's my pic of M31 from yesterday evening:

SW 80 ED with FF/R on HEQ5. Canon 50D at 800 ISO. 11 x 180s subs, with 9 darks. Stacked in Nebulosity 3 and processed in PS CS3.

I like some of the dust lane detail, but there's so much noise coming through in the background and it just lacks any punchy colour to it... I've run out of ideas as to how to make it better.

So, any input, I'm a big boy, so can handle constructive criticism, would be greatly appreciated!

Thanks,

Gav.

[carastro]

M31 is quite difficult to bring out any colour.  Try increasing the saturation slightly.  Also fiddle with the selective colour to see if you can drag some colour out.

Carole

[lensman57]

Hi folks,

I've been fiddling around with this for the last while and seem to have hit a brick wall... here's my pic of M31 from yesterday evening:

180sStacked02Processed-sm.jpg

SW 80 ED with FF/R on HEQ5. Canon 50D at 800 ISO. 11 x 180s subs, with 9 darks. Stacked in Nebulosity 3 and processed in PS CS3.

I like some of the dust lane detail, but there's so much noise coming through in the background and it just lacks any punchy colour to it... I've run out of ideas as to how to make it better.

So, any input, I'm a big boy, so can handle constructive criticism, would be greatly appreciated!

Thanks,

Gav.

Hi Gav,

That is a pretty good capture with nice detail. Both M31 and  M33  appear to image with quite a bit of background noise, the only solution is the right exposure length and a very large number of them to smooh the capture. Just over a couple of weeks ago I did my 2nd capture of M31 with a Canon 1100d @ iso 1600 and 31subs of 150s , the image was very noisy, I think that I would have been better off with 300s exposure and the same number of the subs  but with 300s I wouldn't have had to stretch the data so much so the noise could have been better contained. 

A.G

[ollypenrice]

Saturation is a terrible noise monster so in a noisy image I'd try to avoid it, really. Here are two tricks to try which lift colour without noise. Both are Photoshop.

Make 2 copy layers.

In the top layer change the blend mode from Normal to Soft Light.

Flatten top layer onto middle layer so now you have 2 layers.

Change blend mode from Normal to Colour, put on a slight Gaussian blur (Between 0.5 and 1) and flatten.

Repeat as necessary.

And/or

Change image mode to Lab Colour.

In Channels make 'a' channel active and in Image-Adjustments lift the contrast be a crazy amount like 30. Do exactly the same for 'b' channel. 

Return to RGB mode.

Note that the Lab technique needs space on the left of the histogram pedestal or it will probably black clip, so be aware of this.

You can noise-reduce the sky by selecting it using the Colour Range tool and experimenting with fuzziness to get all the background but nothing much else selected.

Then run a noise reduction filter on it. Also you can zoom into pixel level and see if there are any obviously wrong pixels in there. You often get green ones but other rogue colours appear. Select them using Colour Select with fuzziness around 8 (but experiment) to select a sub set of the rogues. Got to Filter-Noise-Median and use the lowest value which sorts them out. Then move onto a different colour of rogues if such there are.

These and many other ideas can be found in the excellent book Lessons From The Masters, Ed Robert Gendler.

Olly

[PhotoGav]

Excellent, thank you Olly - I will give those a go. Sounds like a useful book.

[StuartJPP]

Some great advice there from Olly...

I recently reprocessed one of my very first proper attempts at astrophotography and it just happened to be M31 (of course). I have been trialling PixInsight which seems to do a great job of stacking DSLR images although I can't attribute the difference in processing to PixInsight as I have (hopefully) improved since my very first attempt and I didn't use PixInsight solely to get at the end result. You may be surprised at just how much you may have captured and these cold/windy/rainy/cloudy nights are good to use to reprocess and reprocess (and watch Youtube vids) until you can't get any more out of the data you have got.

I found this VERY long but it had some great tips in it:

http://www.astronomersdoitinthedark.com/dslr_llrgb_tutorial.php

Here's a before and after and a link to my original thread:

http://stargazerslounge.com/topic/194102-reprocessed-my-very-first-astro-image-before-after/

[PhotoGav]

Stuart, thank you for your response. I'll have a look at the tutorial and hopefully will manage to create something approaching what you have there. Beautiful M31!

Oh the curve, it's steeper than I ever realised!

[foundaplanet]

Saturation is a terrible noise monster so in a noisy image I'd try to avoid it, really. Here are two tricks to try which lift colour without noise. Both are Photoshop.

Make 2 copy layers.

In the top layer change the blend mode from Normal to Soft Light.

Flatten top layer onto middle layer so now you have 2 layers.

Change blend mode from Normal to Colour, put on a slight Gaussian blur (Between 0.5 and 1) and flatten.

Repeat as necessary.

And/or

Change image mode to Lab Colour.

In Channels make 'a' channel active and in Image-Adjustments lift the contrast be a crazy amount like 30. Do exactly the same for 'b' channel. 

Return to RGB mode.

Note that the Lab technique needs space on the left of the histogram pedestal or it will probably black clip, so be aware of this.

You can noise-reduce the sky by selecting it using the Colour Range tool and experimenting with fuzziness to get all the background but nothing much else selected.

Then run a noise reduction filter on it. Also you can zoom into pixel level and see if there are any obviously wrong pixels in there. You often get green ones but other rogue colours appear. Select them using Colour Select with fuzziness around 8 (but experiment) to select a sub set of the rogues. Got to Filter-Noise-Median and use the lowest value which sorts them out. Then move onto a different colour of rogues if such there are.

These and many other ideas can be found in the excellent book Lessons From The Masters, Ed Robert Gendler.

Olly

Thank you Olly, very useful..