Red cast to LRGB images

[blinky]

I have followed a couple of Pixinsight tutorials on LRGB but seem to not be able to get a nicely balanced image.  The next target after M31 the other night (See my other post about that) was M45.  I got about 3 hrs of LRGB data but for some reason the Red channel seems to have, well Im not sure to be honest! It looks almost like light pollution or clouds but cant be since its only in that channel.  I can only think that it's actually OK and Im doing something wrong in my workflow which was roughly as follows:

Stack and Alight etc

DBE

noise reduction

Linear fit against the L

LRGB combine 

Photometric calibration

Background Neutralisation (make no difference!)

Then Levels/Curves/Saturation Boost/More noise reduction etc

 

Here are JPG's of the channels and what I manged to produce - All channels have been stretched exactly the same:

For some reason the images below are Blue, Green, Lum, my attempt at processing and Red is last

[Shibby]

I'd say it's light pollution, which always shows up more in the red channel due to sodium street lights, even though many have now been replaced with whiter LED lights.

[blinky]

Ah,thanks for that, makes sense.  I do have a light pollution filter but have not used it since moving out of town. Maybe I should start again!

[wimvb]

That looks very nice already.

 

I think you may get even better results if you apply lrgb combination after stretching. Use channel combination of your r, g, and b masters. Then dbe, colour calibration, etc. After stretch of rgb, and stretch of l you do lrgb combination.

Process the rgb image for best colour. You can safely do heavy noise reduction. Process L for best detail, use noise reduction sparingly. Then combine.

Good luck

[blinky]

Thanks for the tips! Had another go and it's a lot better but your idea sounds like the way forward

[martin_h]

There is a lot of dust around M45, and apart from around the main stars, will show as red.

[newbie alert]

Looks nice data, what's your setup as the stars around the edges look like maybe  you  need a spacer

[blinky]

28 minutes ago, newbie alert said:

Looks nice data, what's your setup as the stars around the edges look like maybe  you  need a spacer

Yes, I think I need to add more spacers as the focal reducer is a tad too close.....  The setup is:

ZWO ASI1600MM Pro

10mm spacer (I think - cant check 'cos Im at work)

Telescope Services Off Axis Guider

ZWO 8 Position Filter Wheel (with LRGB and Ha, O3, SII Filters)

Altair 1.X Flattener

Altair Optics 70mm frac

 

[wimvb]

1 hour ago, blinky said:

ZWO ASI1600MM Pro

10mm spacer (I think - cant check 'cos Im at work)

Telescope Services Off Axis Guider

ZWO 8 Position Filter Wheel (with LRGB and Ha, O3, SII Filters)

If you swap the filter wheel and the spacer, you get less vignetting, and the guider will get more signal. Especially with nb imaging, life will be a lot easier.

Camera - fw - guider - (spacer) - reducer - scope

[newbie alert]

1 hour ago, wimvb said:

If you swap the filter wheel and the spacer, you get less vignetting, and the guider will get more signal. Especially with nb imaging, life will be a lot easier.

Camera - fw - guider - (spacer) - reducer - scope

Agreed.. not that you have any halos but I think the closer the filters are to the sensor the better..

Plus 1 for the oag in front of the filter wheel

[ollypenrice]

I don't think the colour's far out at all,  just a tad too red in the lower brightnesses. I'd expect DBE (at the linear stage) to sort this out, perhaps if you increased the tolerance value slightly. Failing that you could bring in the black point in red or lower the grey point in red for a global reduction. It's great to see those faint red hints in the lower left nebulosity, though. Don't lose them!!

On the other hand, what's creating those curious dark red artefacts around bright stars. Each bright star is surrounded by four dark circles, above, below and to each side. These don't seem to be in the individual channels so processing is creating them.

Do I gather you stretch the RGB colours separately before combining? I never do that, nor does anyone I know, to the best of my knowledge. NB imagers often do, but not RGB imagers, I don't think.

Olly

[Laurin Dave]

38 minutes ago, ollypenrice said:

On the other hand, what's creating those curious dark red artefacts around bright stars. Each bright star is surrounded by four dark circles, above, below and to each side. These don't seem to be in the individual channels so processing is creating them.

Olly

They look like ASI1600 microlensing artefacts to me.. unavoidable it seems (to me at least) around bright and not so bright stars.. easiest to see on the blue channel 

Dave

 

[ollypenrice]

48 minutes ago, Laurin Dave said:

They look like ASI1600 microlensing artefacts to me.. unavoidable it seems (to me at least) around bright and not so bright stars.. easiest to see on the blue channel 

Dave

 

Still, they seem to emerge far more strongly in the RGB than in any other channel...

Olly

[Laurin Dave]

59 minutes ago, ollypenrice said:

Still, they seem to emerge far more strongly in the RGB than in any other channel...

Olly

Pretty sure that's what they are, first thing I imaged when I got the same camera was M45. Everything looked fine until channel combine when they showed up.  Maybe there's a processing routine in PS or Pi that will mitigate them.   Recent thread from Cloudy Nights about them if anyone's interested.   https://www.cloudynights.com/topic/639998-removing-asi1600-microlensing-artifacts/   . Great camera though.   Just avoid bright stars if the effect displeases you..   

Dave

[ollypenrice]

23 minutes ago, Laurin Dave said:

Pretty sure that's what they are, first thing I imaged when I got the same camera was M45. Everything looked fine until channel combine when they showed up.  Maybe there's a processing routine in PS or Pi that will mitigate them.   Recent thread from Cloudy Nights about them if anyone's interested.   https://www.cloudynights.com/topic/639998-removing-asi1600-microlensing-artifacts/   . Great camera though.   Just avoid bright stars if the effect displeases you..   

Dave

How about combining the colours in AstroArt? You can download a free trial version which won't save but might give better results. If you try this, begin by opening your three colours and go first to Image-Align and choose Star alignment, Translation and Rotation. Apply and then go to Trichromy and put red in red, green in green and blue in blue (of course!)

Olly

[Laurin Dave]

 

2 hours ago, ollypenrice said:

How about combining the colours in AstroArt? You can download a free trial version which won't save but might give better results. If you try this, begin by opening your three colours and go first to Image-Align and choose Star alignment, Translation and Rotation. Apply and then go to Trichromy and put red in red, green in green and blue in blue (of course!)

Olly

Thanks for the tip Olly, I'll give that a go, see what happens and let folk know.

Dave