Getting star colour 'in' stars...

[StargeezerTim]

Hi folks.

Does anyone have any tips for getting star colour inside the stars or processing tips to improve them? I use DSLRs and the star colour seems to be contained at the edge of stars with the centre staying white. In the crop attached I used iso 400 to try and ensure they were not blown. It always seems to be like this. its not areal problem but any help and tips welcome. Cheers, Tim.

 

[happy-kat]

Is that a camera lens? Is it a bit of red and blue CA?

Your smaller less bright stars are all orange looking at that.

[PhotoGav]

What length subs have you used in the above image? You might find that some very short subs capture the star colour to the cores. I constantly suffer from white cores. I reckon that@ollypenrice and @Barry-Wilson are the masters of rich star colour on here - they might have some crafty technique suggestions to share with us? I look forward to reading what is suggested.

[StargeezerTim]

5 minutes ago, PhotoGav said:

What length subs have you used in the above image? You might find that some very short subs capture the star colour to the cores. I constantly suffer from white cores. I reckon that@ollypenrice and @Barry-Wilson are the masters of rich star colour on here - they might have some crafty technique suggestions to share with us? I look forward to reading what is suggested.

They were 4 minute subs... I also look forward to Ollie's and Barry's suggestions.

 

[StargeezerTim]

26 minutes ago, happy-kat said:

Is that a camera lens? Is it a bit of red and blue CA?

Your smaller less bright stars are all orange looking at that.

No, it was a Star 71 scope. I don't think its CA. I could remove the colour edging in PS but then there would be no star colour.

Edit. Here is the result after using the defringe PS function. The is some yellow in the cores but no blue...

 

[pipnina]

11 minutes ago, PhotoGav said:

What length subs have you used in the above image? You might find that some very short subs capture the star colour to the cores. I constantly suffer from white cores. I reckon that@ollypenrice and @Barry-Wilson are the masters of rich star colour on here - they might have some crafty technique suggestions to share with us? I look forward to reading what is suggested.

3 minutes ago, StargeezerTim said:

They were 4 minute subs... I also look forward to Ollie's and Barry's suggestions.

 

Might be able to get colour by running soft median blur on AB channels in LAB mode? Wither in photoshop or gimp.

I'm no expert, it might not be ideal or work, but it could be worth trying?

 

[PhotoGav]

1 minute ago, StargeezerTim said:

They were 4 minute subs... I also look forward to Ollie's and Barry's suggestions.

 

Yup, that's quite long for a star cluster, so I'm sure much shorter subs would give you the core colour. Perhaps 60 or 120 seconds? Time to experiment, should we ever see clear dark nights again...!

Funnily enough, my current target is also The Beehive Cluster. Here's my initial quick experimental process with just one hour per RGB channel in 300s subs:

Yes, white core syndrome here too! I will be trying out some short subs for this one.

Good luck,

Gav.

[StargeezerTim]

28 minutes ago, pipnina said:

Might be able to get colour by running soft median blur on AB channels in LAB mode? Wither in photoshop or gimp.

I'm no expert, it might not be ideal or work, but it could be worth trying?

 

Thanks...I had a go with the Gaussian blur and some Layers. It is possible to blur the colour in to the middle but the stars have become quite soft... There is hope 

[iansmith]

I too struggle with this,but I have found that shorter subs help. I use 150s subs for the RGB background. After you've blurred the stars to get the colour, try a  little colour saturation (in your program of choice) and then use a sharpening tool to make them nice and solid again. I find if I do that, followed by a size reduction step or two for the larger stars, the stars star to look a bit more colourful.

Cheers, Ian.

[wimvb]

Stars that are overexposed will never show colour in the core. Stars that are not overexposed, can get colour in the cores as long as they are not stretched to saturation.

In PixInsight, you'd use masked stretch. In PS probably layers. You can also try Mark Shelley's arcsinh colour preserving stretch.

[Stub Mandrel]

In PS try splitting the image into two.

Use Noels 'increase star colour' along with decent gaussian blur to colour up but soften the stars in bottom layer.

Set the top layer to 'luminosity' to restore sharpness.

 

[ollypenrice]

I suspect that my star colour is in no small measure down to my camera, the much maligned Atik 11000 with sluggish, noisy Kodak sensor and terrible-looking numbers on the spec sheet! But it has d

                                                       e

                                                       e

                                                       p wells and doesn't saturate easily! (I think it's a great camera. I don't get comparable star colour from my Sony chipped Atik 460 and, by the way, I have more work to do to get the background sky clean on this camera as well.)

Where possible I use the RGB-only layer for my stars. This is easy in the case of pure stars-on-background. I just get the RGB and LRGB backgrounds to exactly the same value, put the LRGB on top and erase the stars.

I also use Noel's Increase Star Colour but you have to be careful because sometimes it will exaggerate differences in colour between one side of a star and another and it can also swing the stars awry on the cyan-magenta axis.

Olly

[Barry-Wilson]

For me, it is the sensor I use with 5.4micron pixels and plenty of RGB subs that helps.

For processing, using PI the tools are named differently to those in PS but are aiming to achieve the same result.  In the linear phase I use the Repaired HSV Separation script which aims to improve colour within the star core.  This requires a re-combination back to RGB using Channel Combination in HSV mode.  I use a masked Stretch for the RGB as well.  From time-to-time I also use some convolution on a cloned RGB image protected with a carefully constructed StarMask to help blur the colour within the stellar core, then blend this result back into the original RGB.  I am now more frequently than not adding Luminance to my RGB via CieLab mode in ChannelCombination or combining this method with the LRGBCombination in some direct proportional blend in PixelMath.  Gentle, ie very small amounts of, colour saturation also helps; sometimes iteratively, always with a good StarMask.

I regularly create StarMasks of different scales enabling stars of certain sizes to be isolated for processing; often combining masks with max(starmask1, starmask2, .... etc).  Don't forget that sometimes you need to use Convolution to help round out the mask stars.  There are a number of techniques to help produce the right mask and Warren Keller's book or DVDs are a good reference source.  I will if needed create a mask to isolate a single troublesome star: using PixelMath, you can create a clone with all pixels of value 1, then another clone of all pixel values 0.  Noting the centre co-ordinates of the star, using Clone Stamp of the correct pixel size, softness etc, you can then create a mask for a single star (or a small number) by placing the clone stamp at the exact co-ordinates of the star.  Using convolution you can then feather the edges to the degree required.

The above does take time and patience - but it is fun, right?

I have a couple of PI tutorial's on my smugmug website and I will endeavour to get round to creating one on bespoke StarMasks.

HTH

[PhotoGav]

Thank you @ollypenrice & @Barry-Wilson for your interesting replies. Not that I got much of what you said Barry, you and your PI wizardry. You make it work though!

I look forward to gathering a load more data on the Beehive and seeing what I can produce.

@StargeezerTim - good luck with your continuing collection and I await your version with interest. Thank you for asking the question - it was a good'un!

[carastro]

I think part of the secret is not to over expose and over stretch your stars in the first place.

Olly's idea of using the RGB stars and removing from the LRGB processing would no doubt help with that, and I even resorted to doing just that myself once not realising it might be a regular process to some imagers.

I was watching a video yesterday from Adam Block (a bought one) and he talks about using lab colour in Photoshop to increase the colour in certain parts of the image, and if you select/expand and feather the stars you could use it for that too.  

Photoshop: Mode/lab colour.  Use the a) channel for red and green adjustments and b ) channel for adjusting blue and yellow using the Brightness and contrast tool (contrast tool slide to the right).

This would only work if you haven't previously saturated or over stretched the stars though.

Carole 

[StargeezerTim]

2 hours ago, carastro said:

I think part of the secret is not to over expose and over stretch your stars in the first place.

Olly's idea of using the RGB stars and removing from the LRGB processing would no doubt help with that, and I even resorted to doing just that myself once not realising it might be a regular process to some imagers.

I was watching a video yesterday from Adam Block (a bought one) and he talks about using lab colour in Photoshop to increase the colour in certain parts of the image, and if you select/expand and feather the stars you could use it for that too.  

Photoshop: Mode/lab colour.  Use the a) channel for red and green adjustments and b ) channel for adjusting blue and yellow using the Brightness and contrast tool (contrast tool slide to the right).

This would only work if you haven't previously saturated or over stretched the stars though.

Carole 

Thanks Carole, and all those who contributed. The thing that made the difference for me was making a mask, just allowing work on the bigger stars, then switching to Lab mode and using the saturation slider a little... I thinks its come out pretty good... compared to my first go.  It does something odd to the yellow stars... I got a few bicolour yellow blue stars that had to be erased! I have a way that works 

 

[carastro]

Glad it worked, haven't used it myself yet except I tried it out on a couple of old images while I was watching the video.

Carole 

[clarkpm4242]

If you can trawl through this extensive library...

http://www.clarkvision.com/articles/nightscapes/

...there lies within free software downloads and a method of stretching images that retain the star colour.

I have used it, and it does work.

Paul

[Hallingskies]

I think your first image is really quite good to look at.  Didn’t really understand a lot of what followed. With all of the expensive software around these days, I think it’s only too easy to overcook things...