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Old 27-07-2010, 01:01 PM
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How do I get rid of the pink and gain red

I have been over Rob Gendlers processing tutorials and am wondering how when using Ha data that I end up with lovely reds as seen by many images with Ha?

Currently I am getting pink or a plastic looking nebulosity. See these images.

Click here

And here

How do I maintain nebulosity and yet get the colour right?

I would appreciate your advice.
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Old 27-07-2010, 01:33 PM
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h0ughy (David)
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http://pixinsight.chttpom/examples/M57-CAHA/en.html as an example and http://blog.deepskycolors.com/PixIns...libration.html - hope it helps?
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Old 27-07-2010, 01:41 PM
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Good question. Not sure if I recall this correctly, in Photoshop I think you can switch from RGB to LAB color, and change the contrast in the A channel.

Now, how to avoid green stars?
James
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Old 27-07-2010, 01:51 PM
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No idea sorry Paul, but if it is any consolation, you are not alone, I get them as well.
There will be an answer.
Gary
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Old 27-07-2010, 02:19 PM
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Paul,

It would help if we knew what your work flow was.

Are you DDP stretching or just doing a standard histogram stretch ?
Is your Ha added after the final LRGB blend or in the middle.
Are you double luminance layering

What is the opacity of your Ha Luminous channel ?

I note that the Blue channel is clipped at the white point of your stars, green is also clipping.
Thats less than ideal

Ha stars are almost always different sizes to normal RGB stars so that has to be dealt with too

Cheers

Rally
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Old 27-07-2010, 04:05 PM
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David, I will take a look at that.

Rally,

Standard histo stretch but not much given that I am pushing high back ground ADU on all my colours.

I have tried adding Ha in CCDstack as Lum or in combination with Lum at around 40-50%. I have also tried adding it as luminosity in Photoshop and have tried a double luminosity layering too. Each time pink is the nebulosity colour or going too plastic. When I am using Ha Lum I am using it as no greater than 50% as directed by Rob Gendler.

I know about the white point clipping as I am trying to push the blue and Green and reduce the red to have a balanced impact on the colour. I don't agree with having to deal with the size in stars. This is a common point that many imagers get hooked up on. Halo colours are present in all Ha added images that I have seen across the internet.

So how do I prevent the pink?
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Old 27-07-2010, 04:29 PM
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Paul, the only way I have been able to increase red and reduce the pink is.
1. Reduce the intensity of the Ha when used as a luminance. Keep sharpened detail but just reduce the overall intensity.
2. Blend the unreduced Ha with the red channel before combining the colour channels.
3. Increase the saturation level of the combined image (Red) prior to combining the luminance layer.
4. Combine the luminance layer in photoshop rather than in CCDStack wher you have a bit more control of the blending levels.

It can be a bit of a juggling act but it does work to some degree. I even use a mixture of all these ideas to try and lift the red. Sometimes with better results than others times.
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Old 27-07-2010, 04:31 PM
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Paul,
Try this is CCDStack and see if you like it. Normalise your Ha, L, R, G and B. SUM Ha + R, SUM Ha+L (or mean or whatever)
Then color combine, using Ha+R for R, Ha+L for L.
James
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Old 27-07-2010, 07:17 PM
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Ok been trying a few things. I am happy with the background now and the colour is getting close but I still think it is a bit fluro. I have using Rob Gendlers image to compare.

Doug I used your tip about saturation of the reds prior to using the Ha as luminosity. No clipping but very close.

James I will try that method and see what transpires.

The first image is the old image and the second is the new image.

thoughts?
Attached Thumbnails
Click for full-size image (Lagoon HaRGB 105 45 75 75 cs 6e.jpg)
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Click for full-size image (Lagoon HaRGB 105 45 75 75 cs 6f.jpg)
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Last edited by Paul Haese; 27-07-2010 at 07:29 PM.
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Old 27-07-2010, 09:16 PM
rally
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Paul,

I think 50% Ha for luminance is possibly pushing it a bit high - the problem is that the recipe is different for different subjects, so its definitely not a one size fits all.

The Ha data shows all the nice detail so its very tempting to try and use it to the max.

I would be experimenting from 20-40%
I recall doing the same thing and dropped Ha right back and blended it with normal L, it ended up with around 25%.

Of course there is always the method of removing the stars and then adding them back in again later after you have tweaked the nebula !
Don't laugh - it does work.

Most of your stars are white in the centre with blue halos, so I am wondering if you clipped your stars during the stretching process at an earlier point while keeping an eye on the nebulosity.
The fact that you are pushing blue and green and boosting red to get rid of the pink is possibly a major contributor.
The Salmon Pink comes about as a result of adding Luminance and losing saturation not because you actually lost Red, thats byproduct of working in RGB colour space.

Controlling your stellar profiles to correct for colour distortion in processing by using DDP stretches for both RGB and L (or HaL) separately will help keep your stars their natural colour, but adding Ha afterwards is yet another process to be careful of,
So just wondering what the stars were like before you added the Ha ?

What was the FWHM of your LRGB and Ha images - could it be that some (eg B and G) were larger than the others ?

Cheers

Rally
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