First ever attempt at HaRGB on NGC6888

[SlimPaling]

Hi ...

At last I have started to delve into using my Ha filter ... I incorporated 6 x 500 sec Ha subs to some 300 sec RGB subs a few days ago.

Spent many hours trying to figure out the best way of processing my calibrated & stacked images in Photoshop.

I combined the Ha & Red subs into the base RGB layer and used the Ha as the luminosity layer as per what I have managed to read in books and on the 'net.

I am reasonably happy with results so far, as I can now see a lot more detail in the main nebula, but I keep getting the dreaded "Salmon Pink" colours in the nebulas .... not sure how to overcome this :-(((

Mike

 

[bdlbug]

Great image - but using 100% Ha as luminance substitute is not something I do . Ha is as you’ve found out is  a ‘red’ channel enhancement and Olly Penrice has written many posts with his methodology to copy your RGB image red channel into a new temp image then copy in your Ha image as a percentage  (varies but around 30% as a start) and use blend mode lighten to combine as this will only change or enhance Ha reds when the level exceeds that in your original red channel so the stars will not take on a weird colour as they don’t have enhanced Ha emission - I’m on my mobile so can’t link to one of Olly’s posts but I’m sure someone will.

that should help you get rid of the salmon pink

[SlimPaling]

42 minutes ago, bdlbug said:

Great image - but using 100% Ha as luminance substitute is not something I do . Ha is as you’ve found out is  a ‘red’ channel enhancement and Olly Penrice has written many posts with his methodology to copy your RGB image red channel into a new temp image then copy in your Ha image as a percentage  (varies but around 30% as a start) and use blend mode lighten to combine as this will only change or enhance Ha reds when the level exceeds that in your original red channel so the stars will not take on a weird colour as they don’t have enhanced Ha emission - I’m on my mobile so can’t link to one of Olly’s posts but I’m sure someone will.

that should help you get rid of the salmon pink

Hi bdlbug ...

Thanks for this .... I have just tried your suggestion ... but I still get the same colour effects ?

If you (or anybody else) can point me to some of Ollie's posts covering this problem I would be grateful ..... not sure what software Olley uses ... but I currently do all of my processing in Photoshop ( PixiInsight is way over my head at the minute!)

After posting my image I realised that I had got some green stars ... so I have just run HLVG through it and have reposted it here.

Mike

[RolandKol]

Maybe it will help if you would post your stacked RAW files also....

Never seen anything like this....

[bdlbug]

Mike

read through this thread - a lot of information and option regards Blending Ha in a RGB image

Bryan 

[AstroAndy]

Hi Mike

Solid image.

I've found this of help: https://starizona.com/tutorial/using-an-h-alpha-image-as-a-luminance-channel/ .

Andy

[SlimPaling]

23 hours ago, bdlbug said:

Mike

read through this thread - a lot of information and option regards Blending Ha in a RGB image

Bryan 

Hi Bryan ...

Thanks for this ... I spent quite a bit of time trying to use this method but ultimately I found some problems. It all worked out until I paste the new HaR image into the RGB "red" channel but it came out totally black with no data. After several attempts  I gave up ?

 

5 hours ago, AstroAndy said:

Hi Mike

Solid image.

I've found this of help: https://starizona.com/tutorial/using-an-h-alpha-image-as-a-luminance-channel/ .

Andy

Hi Andy ..

Many thanks for this. I "Think" that I actually got somewhere with this method.

I have spent quite some time re-doing my Ha and RGB files using this method ... and I seem to have made some progress. The colours look a bit better that my first efforts ... to my eye anyway.

I am attaching my latest variant.

I suspect that I really need to do a lot more Ha images next time I image a similar object.

Mike

[peter shah]

I like your last rendition ...nicely done

[SlimPaling]

46 minutes ago, peter shah said:

I like your last rendition ...nicely done

Thanks Peter ... I feel as if I might be getting somewhere now .... still a long way to go I suspect ?

Mike

[wimvb]

+1 for the last (latest?) rendition.

If you add stretched luminance to an RGB image, even if that luminance contains Ha, this will add lightness contrast to the colour contrast that is already in the image. As a result, colours will become brighter, and "brighter red" in this case means red towards white, which is pink. If you extract luminance from a "perfectly balanced" colour image, you'll find it to be rather dull. This means that any luminance that you wish to add to a colour image, should be held back in processing as far as contrast is concerned.

Here's the idea in an image:

• top left: bright green to bright red gradient;
• top right: the luminance extracted from the rgb image. (not much contrast, as you can see)
• bottom left: a luminance gradient
• bottom right: LRGB combination of bottom left (L) and top left (RGB). Red becomes pink, and there's a new colour: yellow

[SlimPaling]

24 minutes ago, wimvb said:

+1 for the last (latest?) rendition.

If you add stretched luminance to an RGB image, even if that luminance contains Ha, this will add lightness contrast to the colour contrast that is already in the image. As a result, colours will become brighter, and "brighter red" in this case means red towards white, which is pink. If you extract luminance from a "perfectly balanced" colour image, you'll find it to be rather dull. This means that any luminance that you wish to add to a colour image, should be held back in processing as far as contrast is concerned.

Here's the idea in an image:

• top left: bright green to bright red gradient;
• top right: the luminance extracted from the rgb image. (not much contrast, as you can see)
• bottom left: a luminance gradient
• bottom right: LRGB combination of bottom left (L) and top left (RGB). Red becomes pink, and there's a new colour: yellow

Hi Wim ...

Thanks for taking the time to send this ... not too sure what you are telling though :-0

Are you saying to not give too much luminance to my RGB image but turning down the opacity of that layer?

Cheers Mike

PS: any snow over where you are in Sweden yet? I have relatives in Stockholm they haven't mentioned it yet!

[AstroAndy]

No problem, Mike.

[wimvb]

27 minutes ago, SlimPaling said:

Hi Wim ...

Thanks for taking the time to send this ... not too sure what you are telling though :-0

Are you saying to not give too much luminance to my RGB image but turning down the opacity of that layer?

Cheers Mike

PS: any snow over where you are in Sweden yet? I have relatives in Stockholm they haven't mentioned it yet!

In essence, yes. What I meant was that for LRGB combination to work, you need to "align" the histograms. Generally, B/W images have a lot more contrast than colour images, and if you combine a good looking B/W image as luminance with a good looking RGB image, you will probably get the bleached colour I was referring to. But if you hold the contrast in the luminance back, and let it provide detail in the image, you will get a better result. LRGB processing stems from the time when sensors were a lot less sensitive, and you needed long exposure times. To get good results quickly, you'd shoot a little colour at bin 2x2, and a lot of Luminance at bin 1x1, to provide detail. With modern sensors, and especially with cooled CMOS, you may not need luminance at all. Several imagers only collect RGB data, at bin 1x1. They may then combine the colour data to create a synthetic luminance master. This master is then processed for best detail, and combined with the RGB data, which was processed for best colour saturation/contrast.

No snow here yet, fortunately. We had some last week, but that vanished as the temperature went back to the high single digits. Atm it's cloudy with temperatures close to 10 C.

[don4l]

5 hours ago, wimvb said:

+1 for the last (latest?) rendition.

If you add stretched luminance to an RGB image, even if that luminance contains Ha, this will add lightness contrast to the colour contrast that is already in the image. As a result, colours will become brighter, and "brighter red" in this case means red towards white, which is pink. If you extract luminance from a "perfectly balanced" colour image, you'll find it to be rather dull. This means that any luminance that you wish to add to a colour image, should be held back in processing as far as contrast is concerned.

Here's the idea in an image:

• top left: bright green to bright red gradient;
• top right: the luminance extracted from the rgb image. (not much contrast, as you can see)
• bottom left: a luminance gradient
• bottom right: LRGB combination of bottom left (L) and top left (RGB). Red becomes pink, and there's a new colour: yellow

I like that chart.  It really compliments my processing method.

 

I usually calibrate and stack in CCDStack, and then produce two different Ha versions.  One is used as my red data and the other (less stretched) will be used as an "L" channel. 

I make an RGB in CCDStack.

In my graphics package, I split the RGB into H, S and L images.  I then recombine using the more gentle stretched Ha data as the "L".  This seems to get rid of noise in the G and B Data.

This sounds complicated, but in practice is very quick and easy.

 

I hadn't really understood why it works, but your chart above seems to demonstrate the effect very well.

I'm going to make up some similar charts tomorrow and have a little play.