NGC4631 - LRGB

[JohnP]

OK - this has been doing my head in. I think main issue was trying to get colour through CLS filter - it really screws up the colour balance... rgb still crap but best I can do. On top of the 18x500secs L image I posted early in the week I got 1/2hr. each RGB at Chris's place..

Anyway this is it - not happy with colour but that's it for now (managed to get a bit of star colour but still not sure about balance).

Comments welcome - I've looked at this damn image so long I need some fresh eyes to tell me what's wrong..  I only wish I knew how to do RGB properly - I think I need to do some RGB G2V star calibrations...

Thks,  John.

[Mike]

Wow! It's really good. Stars look a little weird and kind of like 3D spheres. But the colours are great and loads of detail. I like it.

[PhilB]

I like it, John. Really good.

[MarkS]

John,

The colour version looks great!  However, you just have to accept that you won't get a natural looking colour balance on galaxies using a CLS filter - it's simply a fact of life.

Here's an example of an early one of mine with very similar colouring:
http://www.markshelley.co.uk/Astronomy/2008/m51v3_09032008.jpg

However, one advantage is that the CLS filter does emphasize the Ha regions of a galaxy.

For interest, here's a couple of technical points regarding the use of a CLS filter:

1) Using a CLS filter on a continous spectrum object like a galaxy, the filter will halve the amount of (wanted) light coming from the object.  This means that the filter must reduce the unwanted background glow by a factor of 4 just to retain the original S/N ratio (a square root law applies).  So to be worthwhile using a CLS filter (on a continuous spectrum object) the filter must reduce the background glow by a factor of much larger than 4 - if it doesn't, then you are wasting your time.

2) For most discrete spectrum nebulae, the CLS filter does not cut down the wanted light, so any reduction it makes in the background glow makes it worthwhile to use one.

Mark

[Rocket Pooch]

Wow! It's really good. Stars look a little weird and kind of like 3D spheres. But the colours are great and loads of detail. I like it.

Stars are 3D spheres.  I like it as well, most people use these cameras as guide camera's I think they forget thier origional purpose.

Good image John

[JohnP]

Well thks for all the comments makes all the hours slaving over this trying to sort out colour a bit less painful....

I think my initial problem was that when I was combining the L with the RGB the L was way too bright & was just totally washing out the RGB even if I increased the colour saturation to ridiculous levels the colour would barely show through & it would look horrible because of all the noise etc. Once I got reasonable RGB by lowering intensity of L I then spent an age trying to get balance right not only on galaxy but also background. Basically, I searched for images on web of same object & got as close as I could to the majority. I still don't think it's right but close enough - I mean its not like I am ever going to visit it to confirm one way or the other...

Once colour was close I then wanted to try & get a bit of star colour (the smaller stars had some colour but larger ones were totally washed out) - I read up on various techniques for increasing star colour & the one that seemed to work best was to select brighter stars & then do a selective curve adjustment to reduce the intensity of the cores of the stars followed by a 1 pixel application of minimum filter. It certainly helped colour some of the larger stars - I suspect this is the culprit for Mikes 3D globe comment - I will check but I have a feeling the colour of the stars may not go right to the core of the stars (these are still white) & so give a globe type appearance. I may have to selectively use sponge tool or something to spread colour right across star.

Mark - thks for comments re CLS filter - I think you could be right. I am guessing use of CLS filter is justified in Bromley to get the RGB but I would have been better off removing it when I got the RGB at Chris's place.

Anyway thks again for comments - gonna give this a rest now...

Cheers,  John.

[MarkS]

Mark - thks for comments re CLS filter - I think you could be right. I am guessing use of CLS filter is justified in Bromley to get the RGB but I would have been better off removing it when I got the RGB at Chris's place.

Yes, given Chris's dark skies, I would not use a CLS filter for galaxies - but I would use it for nebulae.

Mark

[mickw]

I like the colours John