NGC 1313 in .. wait for it .. colour!

[rogerg]

Hi all,

It is exceedingly rare I publish a LRGB image but here is one. Data from a couple of weeks back I just got around to doing some more work on.

I have attached LRGB and Luminance only. To be honest the Luminance only has more detail - it seems my RGB frames have really brought down the quality of the image?

As per normal I have struggled to achieve a respectable result out of the LRGB data. This final LRGB image actually has the Luminance image overlayed and masked to hide awful green stars! I think they are because of the 2x2 binning of RGB frames or because some RGB frames were slightly softer on focus.

If anyone feels like playing, here are the LRGB frames:
https://www.dropbox.com/sh/jfb56phxg6pe2ii/1Xh1oum3lN

R=20x300s Bin 2x2
G=14x300s Bin 2x2
B=20x300s Bin 2x2
L=20x600s Bin 1x1

ST8-XME, 12" @ 2180mm (0.84"/pixel)

Shown at 1:1.

All suggestions for improvement (other than the obvious "more data would be good") welcomed :)

Regards,
Roger.

[RickS]

Roger,

A very quick & dirty attempt at processing in PI... not sure it's a huge improvement but it's different :)

I was too lazy to do much with the stars but given more time I would have done some deconvolution to make the sizes similar in R, G & B to reduce the halos. Another trick I probably would have tried would be to split the image into L*a*b* and use a star mask to blur the a and b components. That smudges the star colour a bit and can reduce halos and colour up the white centre a bit.

If you're interested I can list the steps.

Cheers,
Rick.

[rogerg]

Thanks Rick,

I love the colour variance you have, the dynamic difference in colours across the galaxy. In comparison mine looks more monotone aside from the bright pink regions. Was that using a Linear Fit or such in PI that got you that good colour variation?

You seem o have lost some fine detail in the galaxy for some reason - looking slightly "blotchy" in parts, perhaps due to what you used to get the star colour better? (looking at the pink detail in particular)

Thanks for your efforts, much appreciate the discussion to improve my poor LRGB attempts.

Regards,
Roger.

[RickS]

Roger,

I did a CosmeticCorrection at the start to get rid of some cold pixels in the Luminance and that left some artifacts in the brighter areas (it even managed to join some small stars together). I think that's what was responsible for the loss of detail. I wouldn't normally use CC this way but I didn't have a master dark for my normal technique... probably would have been better to leave the cold pixels and clone them out later.

For the RGB the processing steps were: [L]RGBCombine, DBE (twice), BackgroundNeutralization, ColorCalibration (with galaxy as white reference), SCNR to reduce green, light TGVDenoise, stretch, ACDNR chrominance noise reduction, Luminance masked curves saturation boost, masked curves desaturate background.

I think the "magic" step was the saturation boost. There's usually plenty of colour lurking in these images but you have to drag it out (and sometimes you have to be more selective about what you do and don't enhance).

Cheers,
Rick.

[Ross G]

Nice capture Roger.

Ross.

[allan gould]

That's a good image Roger and I like the processing
Allan

[rat156]

Hi Roger,

Couldn't do much with the colour. The green subs are out of focus, hence the green rings around the stars.

Here's my attempt at processing, quick and dirty. Perhaps you could gran Rick's colour and the luminance from this...

Cheers
Stuart

[astronobob]

Interesting Rodger, looks pretty decent from here :thumbsup:
I havent done LRGB data & wanted to try in PS but havent Fitts reader ATM after some major reconfiguring whole PC. should get onto it one day ?
All the best :thumbsup:

[rogerg]

Thanks all for your responses. I still love the colour balance Rick achieved and wished I could get that dusty well balanced look with all my galaxy shots. I was making leaps and bounds with PI a few weeks ago. I haven't had the enthusiasm/energy to open the observatory the last couple of weeks but am now tonight capturing some fresh green data, hopefully in sharper focus this time.

Thanks :thumbsup:

[rogerg]

Rick,

I have new green data and have been trying to make something of it.

Your level of wizardry with PixInsight is an order of magnitude higher than mine. I'm wondering, with our Background Neutralisation and Colour Calibration, howdo you select a ROI being that of the galaxy ... Given I have one image file open which is the DBE modified LRGB combined image, do I select that same image for the white and background reference? I'm doing this but not seeing any change in my image ... just a bit confused about how to use the tools :screwy:

And second question ... Saturation Boost - what tool do I use for saturation? I can't find a process for it :screwy:

Thanks!

[RickS]

Roger: to use the galaxy as a white reference you draw a preview which includes the galaxy, or a representative slice of it, and as little background as possible. Use that preview as the white reference in the ColorCalibration dialog. Similarly, you can use a preview of a background area of the image as the background reference.



The easiest way to boost saturation is with the CurvesTransformation process. Just select the "S" curve and play with it.

You won't want to boost the saturation of the faint areas since this will make chrominance noise and faint colour gradients more visible. A technique that works well is to extract the CIE L* (Lightness) component of your image and use it as a mask:


use the menu Image>Extract>Lightness (there's a button you can click as a shortcut) to extract the L* component as a new image which will be your Lightness mask
use HistogramTransformation to stretch the mask and clip the black point to protect the background
apply this image as a mask to the original
now apply the saturation boost (real time preview is useful to get the amount of boost right)
remove the mask unless you want to use it for whatever you're doing next

Let me know if you have any problems. Good luck with the new data.

Cheers,
Rick.

[nebulosity.]

I had a play in Nebulosity, not much to look at compared with yours :lol:

Cheers
Jo

[atalas]

Roger Its actually a very nice galaxy,and sure a few technical issues to over come but looks to me you'll get there soon!

[alpal]

Hi Roger,
I had a go at processing your galaxy.
What do you think?
Just edited to give more colour to stars & make them softer.
It was processed in : Fits Liberator, DSS, PS CS5, Fitswork4.

cheers
Allan

[rogerg]

Thanks Allan, your result looks similar to what I'm now achieving since acquiring the new green data. What my attempts (and yours I think) lack is the variance of colour Rick achieved which shows that yellow dusty look together with the blue and the pink of nebulosity.



Thanks Atlas :) It is a nice and interesting galaxy.



Thanks Jo, yeap, similar to what I'm seeing now :)



Thanks again Rick ... I'm working through your notes and various attempts ... stay tuned!

[alpal]

Alright Roger,
a different stretch on the Luminance to reveal fainter details & altered colours.
I kept more of the noise in it.

cheers
Allan

[alpal]

And the same crop as Rick's.

[rogerg]

That certainly does have the better colour balance I'm aiming for :thumbsup: Very subtle difference but some how I will get there.

[alpal]

Yes & if you wanted more colour: