M13 RGB & LRGB comparison

[fwm891]

Just a quick test to see if adding a luminance layer to an RGB image of M13 (and probably other star clusters) would make any difference in a beneficial way ? Comments please.

Data for the test: 20x20s subs in each RGB set, 40x20s luminance added to the LRGB image

Scope MN190, Camera Atik 383L+, Baader LRGB filters. Camera running at -10°C.

RGB image:

LRGB image:

Colour has shifted on uploading

[nephilim]

Lovely image of my favorite glob

Steve

[michael.h.f.wilkinson]

The LRGB is a bit snappier, touch less noisy, in my opinion.

Nice sharp images, and like the galaxy in there as well (NGC 6207)

[fwm891]

Thanks Steve & Michael,

Interesting note there on the LRGB, I found (looking at the original files) that the RGB had better colour and that the LRGB had tended to 'whiten' the stars too much...

There's also a smaller galaxy between M13 and ngc6207 - must find out what one it is?

[Gina]

With a close look the LRGB is definitely sharper Nice image Francis

[badgerchap]

LRGB is definitely sharper, and I'd say the core is a touch brighter too. Great shot though either way

[fwm891]

Thanks again everyone, seems the preference is for the LRGB. My initial feeling has been that the L brightened things too much and detracted from the colour content of the RGB alone.

Probably going to have to concede on this one and shoot LRGB's in the future. M13 is quite bright so it should help more on the dimmer less contrasty clusters.

[michael.h.f.wilkinson]

Thanks Steve & Michael,

Interesting note there on the LRGB, I found (looking at the original files) that the RGB had better colour and that the LRGB had tended to 'whiten' the stars too much...

There's also a smaller galaxy between M13 and ngc6207 - must find out what one it is?

I see what you mean. I think there is an even smaller one at (roughly) the 5-o'clock position with respect to M13, and even closer in. Might be an faint optical double however.

[ShineOn]

There's also a smaller galaxy between M13 and ngc6207 - must find out what one it is?

That'll be PGC 208507. Nice image.

Simon

[Tom OD]

I think the LRGB is a bit better, less noisey, and sharper. It made a big difference to the galaxy. Good job.

[fwm891]

Simon & Tom OD, Thanks for the comments and information re small galaxy.

Clouded out here for a few days - so I'm reading the AA5 manual ... you never know I may learn something

[Stargazer33]

Clouded out here for a few days - so I'm reading the AA5 manual ... you never know I may learn something

Things must be bad if you have resorted to reading a manual!

Very nice images. M13 was another one of my WOW moments last year when I saw it for the first time. It was interesting in my general ep, but then I put my 18mm in and hand on heart I did actually say out loud "oh WOW"!

I think I prefer the LRGB image...just. The core is sharper although it is starting to burn out. You have also lost some of the redder stars around the outside of the cluster, but I think the LRGB one just edges it.

[fwm891]

Thanks Bryan, It's a long time since I've done any visual observing with any more than bins, but like you M13 is just awesome in an eyepiece for the first time, (and subsequent views as well!)

[Uranium235]

Looks like you got the propellor too, nice job.

Try having a tinker with layer masks so you can get stars all the way to the core.

[fwm891]

I'm currently restacking all the subs using: dark and bias frame with different blend modes in AA5, this is producing much cleaner background and better gradations to the colour components, there are more luminance subs so they were cleaner to start with.

I'm also leaving it until the last possible moment to transfer the fit files to 16 bit tiffs for work in PS where I use some of Annie's actions to combine either RGB or LRGB images.

The RGB combining feature in AA5 is very good, but I'm not so keen on the LRGB synth routine to add the L layer to the RGB image. But still playing with this so time will tell.

[Matthew]

Well done Francis M13 is a favorite of mine and you've imaged it superbly,I prefer the LRGB image.

[andyo]

Nice image,the LRGB looks sharper and shows the core better

[ollypenrice]

I would not use a luminance layer for stars or clusters, even globulars. If you add signal you'll reduce noise, that's a given, and has happened here. However, wherever possible I now remove luminance from stars because it simply brightens their cores and burns out their colour in so doing. If you want smaller stars, and you want them to have strong colour to the core, shoot them in RGB only. To compare like with like you'd need to shoot as much total time in RGB as in LRGB. I believe that, if you did that, you'd get a tighter M13 in RGB only.

Where luminance comes into play is in capturing the faint stuff about three times as fast as you catch it from under a colour filter.

When selectively processing bright stars (Trapezium, Alnitak and the usual suspects) it is way easier to do a soft stretch in RGB only than in LRGB and layer it into LRGB for core control. In the 47.5 hour M31 collaboration the starfield itself is made from a miserly hour per channel RGB only. http://ollypenrice.s...TEC CORE-X3.jpg

I think that I first became interested in this technique after a comment from Rob Hodgkinson, to give due credit. It has done more for my starfields than anything else I've yet tried.

Olly

[fwm891]

Thanks Olly,

Noted. Many thanks for the constructive comments above - your jpg link is awesome.

Francis

[Pete Presland]

another vote for the LRGB, clearly see the propeller, and looks like a couple of fuzzies in there as well!

[ollypenrice]

another vote for the LRGB, clearly see the propeller, and looks like a couple of fuzzies in there as well!

Ah yes, the L will be a huge help for the fuzzies.

Olly

[kirkster501]

Hi, whats the very faint line running down, from top to bottom to the right side of the cluster? Its very faint and visible on both images. I am not beign picky - as if a newbie like me would be! - but wanted to know what caused it?

[Uranium235]

Looks like a satellite or meteorite hit, it seems to be part of the RGB data. Sigma clipping or SD mask stacking would sort that out in a jif.

[fwm891]

Hi, whats the very faint line running down, from top to bottom to the right side of the cluster? Its very faint and visible on both images. I am not beign picky - as if a newbie like me would be! - but wanted to know what caused it?

A sat trail - very bright across 1 frame. I should have dropped the frame but final image was intended to be a square crop and the line would have been removed