How can you keep star colour?

[swag72]

Looking at the images produced by Peter Shah, they are vibrant and absolutely full of star colour. In my images I seem to lose this. Now I know that there is a massive difference in price between the two set up's, but is there a general rul of thumb or way of maintaining the colours in the stars?

Or perhaps there's some necessary equipment that you need, for example a CCD and filters. Perhaps great star colour really can be achieved with a DSLR?

Hope there is an answer to my question, other than you need to spend ££££'s!!

[swag72]

I understand about not clipping the highlights to maintain the colour. But, for example, my 1000D (modded) is clicking away now at M66, but already my star colour has gone with 5min subs - I am using a CLS clip filter - So what can I do to combat the white only stars?

[Merlin66]

Provided the star image is not saturated and the RGB data is still there, you can use a G2V star as a reference - this one should be white, to find a colour correction matrix -which when applied - should correct the other star images.

[swag72]

Can you explain in easy terms?!! I think I know what you are saying, but how on earth do you do that?

[Merlin66]

I'm not sure there are "easy terms" - you're looking at some serious manipulation of the RGB components of your image.

Carte du Ciel and other mapping programs can give you the classification of the stars in your field of view. (I use astroplanner V2 - it has a separate catalogue of the G2V stars).

When you find a suitable G2V star, you need to look at your image and see what colour it appears - too blue? too red??

Adjust the RGB sliders in your imaging processing software to give a white star image. The slider positions should then be used for similar images to "correct" the colour balance. if your star images are over saturated (histogram shows it "clipped" at the top end) then you're very limited in making these corrections.

Hope this helps.

[AndyUK]

(Maybe it's cheating, but have you looked at Noel's Actions? There's an action entitled "Increase Star Colour"...?)

[ollypenrice]

(Maybe it's cheating, but have you looked at Noel's Actions? There's an action entitled "Increase Star Colour"...?)

It is not cheating because the star colour you have will be intensified. FIne if it is right, but if it is wrong...

DSLR images do not seem to show much star colour compared with CCD. I don't know why.

PixInsight has an all star colour calibration routine which I find works well, though I haven't been using it long.

But finally, I think we'd all like to know how Peter gets his star (and other) colour so utterly perfect!!! I know he did do a G2V calibration.

Olly

[AndyUK]

(Thanks Olly - I'ev always felt a little guilty going to that action almost by default...!)

[swag72]

I was hoping that someone may point me to something in PI to assist with this. It does seem though that if I want lovely star colour it's going to take a CCD at the very least?

I'll have a look at that PI menu Olly, thanks.

[ollypenrice]

I was hoping that someone may point me to something in PI to assist with this. It does seem though that if I want lovely star colour it's going to take a CCD at the very least?

I'll have a look at that PI menu Olly, thanks.

Sara, it is in one of Harry Page's tutorials. It is called colour calibration on the menu but you can choose the all star method or the nearby galaxy method according to Harry.

One thing to watch is not over stretching and so lifting your bright data off the scale. You can do a second stretch of the linear data in which you look onlly at the stars. When they are right stop, paste that on as a layer, select the stars and erase the rest.

I confess, though, that star colour is not a strong point in my images! At least PI gets rid of the green horrors and I have my own action for de-magentarizing blue stars. Bodge bodge, better to get it right in the first place!!

Olly