Another attempt

[alan4908]

After watching several tutorials on how to process narrowband images, I thought I'd have another go at reprocessing my recent (and first) attempt at a Hubble Palette with IC1396. I think this is an improvement but I'd appreciate any constructive comments 

Alan 

LIGHTS  R:7; G:6: B: 6 x 600s; H:8:O:12:S: 5 x 1800. BIAS: 100; DARKS: 30 x 1800s; FLATS: 40 x 0.2s at -20C

 

Crop of the trunk:

 

[Charic]

.......amazing to think this is all up there, just requiring the right equipment and the skills to process the data.

Well done.

[aparker]

Great result - what tutorials did you watch?

[alan4908]

Thanks for the comments. 

7 hours ago, aparker said:

Great result - what tutorials did you watch?

I watched these before my reprocessed attempt:

1. Don Goldman - how to create a Hubble Palette

Tutorial 9: Clipping layer mask method in Photoshop for tri-color narrband data using Ha, OIII and SII

http://astrodonimaging.com/tutorials/

2. Bob Franke - how to adjust the colour in a Hubble Palette to get pleasing images

http://bf-astro.com/hubbleP.htm

3. Doug Hubble 

Video tutorial on general narrowband processing

NGC281 step by step

https://www.youtube.com/watch?v=A6C7ZVaxKqA

Since I like RGB rather than narrowband starfields, I also use a program called Stratton which does an amazing job of removing stars whilst preserving details.
When I've obtained a starless nebula I then blend the RGB starfield into the nebula via PS Screen, which I think gives a more natural look than PS Lighten.

Download Stratton from here:

http://www.zipproth.de/

Alan

[PatrickGilliland]

Certainly going the right way - a little less saturation will avoid the introduction of colour artifacts and help with the ringing.  But def going the right way with this - Paddy

[alan4908]

13 hours ago, PatrickGilliland said:

Certainly going the right way - a little less saturation will avoid the introduction of colour artifacts and help with the ringing.  But def going the right way with this - Paddy

 

The main item that I noticed when I processed this image was the relatively large noise levels of the SII and OIII data compared to the Ha (I really could have done with more data). I attempted to minimise this impact by using only the Ha as the Luminescence layer and using quite heavy blurring on the colour image to reduce the chromatic noise.  Whilst I think this was largely successful, it wasn't perfect. 

By ringing do you mean the small coloured star halos around the stars, which I presume are caused by slightly too much saturation in the RGB starfield ?  

Thanks for the encouragement Paddy.

Alan

 

[PatrickGilliland]

OIII and SII are always going to be noisier i go with a mix to help alleviate this r=sii*.76+ha*.24, g=ha*.85+sii*.15, b=oiii.  Strengthening the S+H channels by featuring ha in both helps reduce noise in both.  Mixing these to with the noisier oiii is then a little more forgiving.

I then adjust away from the green using SCNR (can also be done with colour tools in PS) to get near to this (some additional colour tweaking is required but you will have the foundation.

Halo's yes - could be poor blending or over saturated 

You could try this

1.  Take your image and create two new layers.  (or you can create 1 but you will have to rename the locked base layer 'colour' and then its is editable, set to colour and a new lum layer)

2.  Set lower layer to colour and upper layer to luminosity.

3.  Add a layer mask to the colour layer then invert (ALT+I to select CTRL+I to invert) should now be black.

4. Select the colour image (not the mask) then apply a heavy gaussian blur to the the image.  Watch the gaussian blur window, in it select a star that has the issue and keep blurring until it all gets kit fuzzy and the ringing effect is gone. You could find you need to go quite high on the slider 30-150 points is possible depending on the star and halo size.

5.  Click OK - nothing has happened yet as masked.  Select paint brush tool and a suitable pixel size 20-60 pixel is good start. Set paint brush foreground colour to white.

6. Click on your colour layer to activate.

7. Now paint around the stars (you can include the star itself but may sacrifice some star colour if so - in NB though thats fine) that have black halo's. (Can be used for any halo - equally as useful where a star is changing the colour of local nebulosity) - you will see the blurred image now apply itself in the selected area.

8. Finally blend the mask in - subject to the effect caused this can be 10-50 %, the eye will tell you when you have enough.

 

It's a go to for me when i need to recover an error.

 

Paddy

 

[alan4908]

Paddy 

Thanks for the processing tips.

I'll definitely try your suggested formula for noise reduction on the colour mapping (r=sii*.76+ha*.24, g=ha*.85+sii*.15, b=oiii) and I think I also need to experiment with your star "deringing" approach .  

As a matter of interest, what do you recommend using for the Luminescence layer - or is this object dependent ?

Alan

[ChrisLX200]

Personally, I don't like to remove _all_ the green because (I think) it adds another dimension of shading which affects the 3D appearance - it differentially shades what otherwise would be a plain brown>blue palette (looking more like a bi-colour in effect). As always, there is plenty of room for personal interpretation in generating your preferred colour palette and some will not agree!

ChrisH

[PatrickGilliland]

3 hours ago, ChrisLX200 said:

Personally, I don't like to remove _all_ the green because (I think) it adds another dimension of shading which affects the 3D appearance - it differentially shades what otherwise would be a plain brown>blue palette (looking more like a bi-colour in effect). As always, there is plenty of room for personal interpretation in generating your preferred colour palette and some will not agree!

 

ChrisH

You're absolutely right Chris (although a lesson i have only picked up on recently) - if used correctly green can add more range to the colour spectrum and provide a less 'processed' feel.  From a personal taste perspective i had previously subscribed to 'green should not be seen' unless a PN approach.  That said a little green may be present and not perceived as primary colour (which i think is the key).

However, in hindsight i have been a little premature previously in the full removal of green.  Leaving some green in  will create more range in the image so even if you adjusted the green much later in the process subject to your taste it would provide more tonal range than my version be it with some green or some more variation to the brown thus maintaining the 3D effect you mention Chris.  I think my view is now 'Green should not be perceived as a primary colour in the image' not quite as catchy  but probably more accurate.    

My new rules are never kill anything 100% as if you do you are likely losing something that can't be recovered later.  In this case green creating tonal range and perceived texture.

However the approach above i think is a solid starting point so hopefully was of help.

Cheers

Paddy

 

[ChrisLX200]

That is what's great about this hobby - no absolute right or wrong but simply an attempt to generate an image with aesthetic appeal. For the purists - you lose no science value if you keep the raw data, astrometry and photometry can still be carried out on that, and indeed, I routinely scan my data for asteroids and report the results

ChrisH

[alan4908]

After taking on board the comments from @ChrisLX200  (green is OK) and  @PatrickGilliland (star halos and colour artifacts) I thought I'd have another go 

My major revelation was discovering why I was getting star halos in the first place:  basically when I was importing the RGB starfield data from CCDstack into PS I wasn't paying attention to the pixel value displayed in CCDstack for the starfield, since quite a few of the stars had values of between 200 and 255 it meant that they where going to be virtually impossible to colour. If you attempt to colour these, you end up with halos.  I also discovered (via one of Adam Block's Cosmic Canvas videos) that an easy way to eliminate halos is to use the PS smudge tool - set it to colour mode with a brush strength of about 40% - I presume this is doing a similar thing to Paddy's suggestion.

On the colour artifacts - these appear to mainly attributable to my use of the star removing program Stratton and insufficient blurring of the resultant image.

So, after implementing a few corrections  and turning down the colour saturation a little, the image below resulted. 

Alan