M81 with some questions...

[Galaxyfaraway]

This is maybe my 3rd attempt at a galaxy and I am trying to figure out the best way of doing it since I live in a red zone of London suburbs.

I took this over 2 nights (well, 1.5 really, as my guiding wasn't working and plate solver wouldn't comply after meridian flip...) with my 8" EdgeHD SCT with 0.7x reducer and Atik 490X. Around 20 Luminance subs at 10 mins each  (1x1) and around 15 RGB subs at 5 mins each, but binned 2x2. I use Astrodon filters but also have an LP filter permanently in my image train. 

Question: should I only use RGB and create a synthetic L channel, given LP, or continue trying with the actual luminance? Gradients are horrible with luminance but RGB doesn't have as much detail (only red filter seems to be more sensitive).

My stars are all over the place (colours pop out everywhere, in the wrong way), how can I control this better?

Also, as I wrote, the red filter seems to have much more detail than the rest and when I add all the channels into PS, the red colour just overpowers everything (and in general, how can I keep the star colours as they are and not have the red and blue go crazy - I am not sure the name for it, but it looks like chromatic aberration on steroids).

Any other general tips would be great...

Thank in advance. GFA

PS: I cheated with the core: just changed the temperature to make it look a bit more glowy; for some reason, I barely had any yellow colour from the data...I will post stacked images, if of interest.

 

 

[Galaxyfaraway]

Here are the images out of DSS, I only adjusted levels a bit (blacks etc) in Lightroom to make them a bit more 'even' in terms of signal and brightness etc and also tried to remove gradients in the Luminance. Then I transferred the files into PS before assembling into RGB, combining with Luminance and colour correcting a bit (using levels for individual colour channels). I then went back to LR (I feel more comfortable in LR than in PS where I am still learning the ropes) where I twisted all the knobs possible to try and make it look like a galaxy...

So luminance was 10 mins at 1x1 (about 20) and RGBs were 5 mins at 2x2 (about 15 of them). I realised that I might be oversampling? Resolution per pixel at bin 1x1 is 0.47" which is too low, no?

1. Luminance, 2. Red, 3. Green, 4. Blue

PS: I have reattached them in full res tiffs, in case it's more useful (wow, it's a generous file size limit this site has..).

 

 

 

 

2019-04-01 12_48.57 L Autosave.tif 2019-04-01 12_50.08 R Autosave001.tif 2019-04-01 12_51.24 G Autosave002.tif 2019-04-01 12_52.42 B Autosave003.tif

[ollypenrice]

Broadband is always going to be difficult from London suburbs because both the LP and the filter to block it will affect the signal strength per filter.

The most powerful anti-gradient tool of which I'm aware is Dynamic Background Extraction in Pixinsight. However, since you have Ps, you could try Russ Croman's Gradient Xterminator plug-in. (The big advantage of DBE, however, is that you can run it on the linear data while seeing its effect on a temporary screen stretch. In truth I use PI only for this tool and its SCNR green noise reduction, but there is a free equivalent on Rogelio's Deep Sky Colors website. It's called Hasta La Vista green. You might find this useful as well.) DBE also carries out a colour calibration across the full range of brightnesses.

In Ps you can use the Eyedropper set to Colour Sampler to put 4 markers on the background around the image. Go for 3x3 or 5x5 Average with this tool. Then the info palette gives you a readout for the brightness per colour at each sample point. If you aim for about 23/23/23 for starters you'll have got your background right and that's always a good starting point. Resist the temptation to black clip the histogram in order to get rid of a colour gradient. You'll also be getting rid of a lot of precious signal. I always concentrate first on the background sky because it is the foundation of the image and, along with the stars, the hardest part to get right.

I think the image as posted shows that you'll find a solution.

Olly

Edit: I doubt that there is any point in imaging at 0.47"PP with city seeing. (You'd also need a guide RMS of less than 0.25arcsecs.) Even an arcsecond image scale can be hard to exploit. I'd bin the L 2x2. At least I'd try it: there are often unpredictable side effects from any change like this but in theory you should be binning, yes.

[Galaxyfaraway]

13 hours ago, ollypenrice said:

Broadband is always going to be difficult from London suburbs because both the LP and the filter to block it will affect the signal strength per filter.

The most powerful anti-gradient tool of which I'm aware is Dynamic Background Extraction in Pixinsight. However, since you have Ps, you could try Russ Croman's Gradient Xterminator plug-in. (The big advantage of DBE, however, is that you can run it on the linear data while seeing its effect on a temporary screen stretch. In truth I use PI only for this tool and its SCNR green noise reduction, but there is a free equivalent on Rogelio's Deep Sky Colors website. It's called Hasta La Vista green. You might find this useful as well.) DBE also carries out a colour calibration across the full range of brightnesses.

In Ps you can use the Eyedropper set to Colour Sampler to put 4 markers on the background around the image. Go for 3x3 or 5x5 Average with this tool. Then the info palette gives you a readout for the brightness per colour at each sample point. If you aim for about 23/23/23 for starters you'll have got your background right and that's always a good starting point. Resist the temptation to black clip the histogram in order to get rid of a colour gradient. You'll also be getting rid of a lot of precious signal. I always concentrate first on the background sky because it is the foundation of the image and, along with the stars, the hardest part to get right.

I think the image as posted shows that you'll find a solution.

Olly

Edit: I doubt that there is any point in imaging at 0.47"PP with city seeing. (You'd also need a guide RMS of less than 0.25arcsecs.) Even an arcsecond image scale can be hard to exploit. I'd bin the L 2x2. At least I'd try it: there are often unpredictable side effects from any change like this but in theory you should be binning, yes.

Many thanks for the reply! I will check out the gradient tools. I simply used the gradient tool and radial filter (which applies a kind of vignetting around the galaxy) in Lightroom, wherever there was a gradient but it made everything too black. I presume Pixinsight's tool works in a  completely different way. This software scares me, as it looks completely gibberish to me on the first glance...

Stars: how does one get more (any!) colour in the stars? (and avoid the massive red and blue halos?). When I put RGB together, there is immediately too much red colour (picture attached) and any tutorials I followed seem to not have such imbalance at the starting point. The stars are white and the only colour is only in the halos...

Binning: 1x1 somehow looks smoother than 2x2. But I understand it might be an illusion.

And lastly: any views on whether to RGB or LRGB for broadband imaging in LP? I read contradictory things about this.

[Galaxyfaraway]

PS: Does the Astronomy Actions Tools still work with the current version of PS CC (I think I have version 20) for mac? And do their gradient removal tools work well? Or is the gradient xterminator tool still better? The astronomy action tools seems like the thing to have for lazy post-processors like myself...Do people still use them?

[ollypenrice]

I don't know if Noel's Actions work on the latest Ps but I find some of them very useful. Increase Star Colour pulls colour from the halo into the core which is fine if the colour is right in the first place! I still use CS3.

Pixinsight can indeed be accused of being written in near-gibberish but DBE is not too hard to fathom. Harry Page's tutorials are helpful.

I don't know whether L helps or hinders in LP but someone should know.

Olly

[Galaxyfaraway]

3 hours ago, ollypenrice said:

I don't know if Noel's Actions work on the latest Ps but I find some of them very useful. Increase Star Colour pulls colour from the halo into the core which is fine if the colour is right in the first place! I still use CS3.

Pixinsight can indeed be accused of being written in near-gibberish but DBE is not too hard to fathom. Harry Page's tutorials are helpful.

I don't know whether L helps or hinders in LP but someone should know.

Olly

Oh I am sure Pixinsight is brilliant! It's just me who is too stupid to learn...Once I get better with PS and actually feel more confident that something can be done with the data at all, I will dive into Pixinsight.

Probably a stupid question but what is roughly the workflow process (after LRGBs are stacked), tutorials seem to vary greatly. Is there one that is particularly close to what you do?

When the 4 channels go to PS, should they be stretched individually first and background adjusted, then combined into RGB, then adding luminance? And should most of the adjustments be done on RGB layer, or together with Lum? I read somewhere you mentioned to add luminance gradually, so the adjustments are all done to the RGB layer or with Luminance added (and image flattened). 

The beginning of processing is kind of puzzling for me, then I see some light on the horizon, especially if the Astronomy Action Tools can help...

Thanks again.

[emyliano2000]

Hi. I have the exact same problem with the luminance. I also live in one of London suburbs, Bushey to be more exact and I keep trying to shoot luminance with no good result. The gradients are horrible and all my efforts with DBE in pixinsight, GradX in PS didn't solve the problem.

Lately I've been getting other weird artefacts and patterns in the luminance stack but I will open a new thread for it because I don't wanna hijack your one.

So far, I only have one RGB photo shot with the mono camera and I decided to do a RGB only instead of LRGB for the same reason. I'm thinking of just increasing the exposure time for each filter to get somewhere close to what the luminance filter would pick up. I even used a baader neodymium instead of the L with no better results.  Don't know.

And to be honest I haven't seen much more in the stretched luminance stack than the stretched RGB blend.

I'm nowhere near giving advice on what should be done as I only have one RGB photo shot with a mono camera in the bag but regarding the RGB blending what I do is process each channel separately until I have a pretty good result and then use an action tool in photoshop from an action pack (Annie's astro actions) that is doing the blending for me.  After that I continue to work on the photo until I have a result that I'm happy with. 

Emil

[Galaxyfaraway]

6 hours ago, emyliano2000 said:

Hi. I have the exact same problem with the luminance. I also live in one of London suburbs, Bushey to be more exact and I keep trying to shoot luminance with no good result. The gradients are horrible and all my efforts with DBE in pixinsight, GradX in PS didn't solve the problem.

Lately I've been getting other weird artefacts and patterns in the luminance stack but I will open a new thread for it because I don't wanna hijack your one.

So far, I only have one RGB photo shot with the mono camera and I decided to do a RGB only instead of LRGB for the same reason. I'm thinking of just increasing the exposure time for each filter to get somewhere close to what the luminance filter would pick up. I even used a baader neodymium instead of the L with no better results.  Don't know.

And to be honest I haven't seen much more in the stretched luminance stack than the stretched RGB blend.

I'm nowhere near giving advice on what should be done as I only have one RGB photo shot with a mono camera in the bag but regarding the RGB blending what I do is process each channel separately until I have a pretty good result and then use an action tool in photoshop from an action pack (Annie's astro actions) that is doing the blending for me.  After that I continue to work on the photo until I have a result that I'm happy with. 

Emil

Wow, I am actually right next to you! (Stanmore). But your skies are probably dark skies compared to mine ? 

I do see some detail in Luminance that I don't see in the RGB, I think, or maybe it's my imagination, it's just the gradients are a pain...(I will attach luminance and red channel again, just for reference). I will download all these tools first and maybe try to process one more time. 

Very nice image with nice star colours! It's interesting with the background: I always imagine it being quite black in space, but apparently it's not as black as one thinks  ? 

[ollypenrice]

18 hours ago, Galaxyfaraway said:

Oh I am sure Pixinsight is brilliant! It's just me who is too stupid to learn...Once I get better with PS and actually feel more confident that something can be done with the data at all, I will dive into Pixinsight.

Probably a stupid question but what is roughly the workflow process (after LRGBs are stacked), tutorials seem to vary greatly. Is there one that is particularly close to what you do?

When the 4 channels go to PS, should they be stretched individually first and background adjusted, then combined into RGB, then adding luminance? And should most of the adjustments be done on RGB layer, or together with Lum? I read somewhere you mentioned to add luminance gradually, so the adjustments are all done to the RGB layer or with Luminance added (and image flattened). 

The beginning of processing is kind of puzzling for me, then I see some light on the horizon, especially if the Astronomy Action Tools can help...

Thanks again.

I never stretch the colours before combining. (I've never tried it, mind you.) I combine my colours in my stacking program, AstroArt, usually at equal weighting, and then stretch this RGB as one image so all channels get the same stretch. Before running my linear RGB through DBE I used to give it an initial stretch in Ps and then look at the histogram in All Channel View. I tried to get the top left of the histo peaks aligned right-left to the same point by moving the black point slider to drag that channel's peak left. Be careful not to clip the data while doing this, though. To get the colours to the same value for the background sky in each channel you can use the black point in Levels and maybe make small adjustments in Colour Balance set to shadows. In preparing my RGB my processing objectives are entirely different from those of my luminance layer. My RGB priorities are simply low noise and strong colour saturation (because the luminance will dilute it). I will often reduce the saturation in the background sky by using the colour select tool to identify it but I want strong star and object colour. Depth of faint structures and sharpness of detail are not at all important in the RGB layer. 

I then process the luminance with the priorities being: background sky to the right level (between 20 and 23 in Ps.) Small stars. Faint structures lifted into view. Bright areas controlled to avoid saturation (which may mean a softer stretch of the same data used as a layer). Noise reduced unobtrusively in faint areas. Details in strong signal sharpened (but stars excluded from sharpening.

I add the L to the RGB in small iterations as explained earlier.

Olly

[emyliano2000]

11 hours ago, Galaxyfaraway said:

Wow, I am actually right next to you! (Stanmore). But your skies are probably dark skies compared to mine

You are more than welcome to come over and shoot your luminance from my back garden if you think it might be better. ?