my comment relates to how to make full use of the color gamut available to you
it is common to find Halpha many times more abundant in an object than [OIII] or [SII]
if you made no levels adjustments at all and combined ha, s2 and o3 together to make a color image then it would be dominated by the color you assign to halpha
so if you boost the signal in the o3 and s2 channels so that the histograms are of similar extent to the halpha then you get maxium use of the color gamut
Let me show you examples:
here is an image where the channels were balanced pretty well; notice how there's no one color that overwhelms the overall blend
here's a somewhat older image that wasn't quite so well balanced (was still developing the method that is so commonly used now by so many)
finally I recommend assigning the channels in the wavelength order for most objects:
Red = [SII]
Green = Halpha
Blue = [OIII]
that assigns the longest wavelength data to the longest wavelength color, Red and so on...
----- Original Message -----
Sent: Tuesday, July 14, 2009 4:12 PM
Subject: Re: [NBI] NGC6888 Putting it Together
Richard,
Thanks for the link to the article, it was helpful.
One question about the histograms. You say that the histograms of the OIII and SII channels should be stretched to closely match the Ha image. Is this true in all cases? NGC6888 seems to be predominantly "red" (if Ha is assigned to red), so wouldn't the resulting color image have a red histogram that is wider than the OIII and SII?
joel
--- In narrowbandimaging@yahoogroups.com, "Richard Crisp" <rdcrisp@...> wrote:
>
> welcome to the group Joel.
>
> I tried to look at your images but they weren't loading. But let me say a few words that may be of some help:
>
>
> I wrote the original article on narrowband imaging and it appeared in S&T in aug of 2005
>
> the draft of the article is here:
>
> http://www.narrowbandimaging.com/tricolor_emission_line_imaging_crisp_page.htm
>
> the key things to keep in mind are to keep the histograms of the three channels untruncated and of similar shape so that you make full use of the available color gamut and avoid having one color (typically hydrogen) dominate the mix
>
>
> ----- Original Message -----
> From: jkeshort
> To: narrowbandimaging@yahoogroups.com
> Sent: Tuesday, July 14, 2009 3:16 PM
> Subject: [NBI] NGC6888 Putting it Together
>
>
>
>
>
>
> Hello,
> I am new to this group, and am new to narrowband imaging. In fact, I'm working on my first narrowband image, a bi-color image of NGC6888 (Crescent Nebula). I feel as though I have good Ha and OIII data with round stars and a sharp image. However, I am struggling with putting them together into a color image. It seems as though when combining the images the color gets completely washed out. I've tried mixing different arrangements, all with the same result.
>
> You can see the Ha image here: http://www.buckeyestargazer.net/New%20Image%202.html It is 2hours in 15min subs through an Orion Eon 80ED, mounted on an LX200GPS. The OIII image can be seen here: http://www.buckeyestargazer.net/New%20Image%203.html
>
> Any advice as to how to combine the images would be most appreciated. Perhaps the best thing would be for someone to take the raw Ha and OIII images and see what they can do with it, then tell me what they did. I'd be glad to send the images to someone willing to do that, but I realize that's a tall order! Thanks in advance for any advice.
>
> joel
>
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