Converting Ha Mono to ‘RGB’

[Matt S]

Hello all
I’m trying to ‘persuade’ my Lunt LS35 deluxe Ha Solar scope and ASI120MM to image the Sun. I have an ASI224MC also, but have been advised to use the 120’s superior resolution.
My question is, having captured and stacked a suitable AVI movie, is it possible to ‘convert’ it into a pseudo RGB colour image in StarTools?
A few pointers would be gratefully received while the clouds smother another bank holiday in the UK…
Clear skies and sunspots galore!
Matt S

[Mike in Rancho]

Hmmm.

What do you mean by pseudo RGB? A mono Ha image would just be varying intensities of...well gray I guess. Even saved as RGB (which ST does), each pixel will have identical values in each channel, thus also all gray.

No variances will have been captured or processed into an image that I can think of in order to even faux up something reasonable, at least that has multiple hues. Not without selective masking, anyway.

Of course if you just wanted the mono gray image to be something other than gray, I imagine that could be done by opening (or perhaps composing, but I'm not sure it would give more options) your already-processed and saved image, but of course as non-linear. In the color module you could then give it a tint, I suppose, using the saturation and channel bias controls. Maybe?

[Matt S]

Mike
Thanks. That’s about the sum of it.
I read an article elsewhere which said that PhotoShop can assign RGB to greyscale images, hence why I wondered whether there is some trickery in StarTools that can do the same. My StarTools skills are still fairly novice, and I haven’t - yet - started exploring the Layer or Compose functions yet (lack of need), which is where I thought this capability might lie.
Best, M

[Mike in Rancho]

Hi Matt,

Well I have done something like that in Gimp, that perhaps is similar to PS? But that is taking known mono images from R, G, and B filters, and then "colorizing" them by (1) conversion from mono to something like sRGB color space, and then giving each the appropriate full color assignment. Then all the layers are flattened and become a single color image.

However, no way to do that here. The conversion into sRGB will still be gray because there's only one channel, in your case Ha.

But I agree that changing your image to "color," even just a single hue, might be more visually interesting than mono gray. In fact, in something like Gimp/PS, you might be able to assign the colorizing to match the shade that Ha would be - 656 a fairly deep red. In ST using color I think you would just be eyeballing it to taste using saturation and bias controls. There may be other options starting off with compose and the interpolate setting (and then matrix choices in color), but I'm not too well versed in that.

[Matt S]

Hi Mike
Grateful for your response. I’ll investigate buying an old version of PS for this purpose: nothing ventured, nothing gained. Doesn’t distract from my admiration of StarTools which continues to work wonders with my data.
Clear skies,
Matt

[Mike in Rancho]

Well, if you like PS and have other uses for it, maybe. But really for limited purposes (or at least as a test) I would just download Gimp rather than go buy anything. Free/open source, and a pretty complete alternative to PS. It will for sure allow you to convert mono to sRGB and then assign a hue to the image.

[hixx]

Hi Matt,
If You just want to assign a color hue to the greyscale, You could do this in ST as well:
1) In Compose module, load Your Ha image in all R, G, B slots
2) In Color module, use Bias sliders to blend coloring
This might not be as intuitive, but should do the job OK without the need to buy anything

cheers,
Jochen

[Matt S]

Hi Jochen

That is really very interesting, and timely given that I am now in a bidding war for PS6! I will certainly give this a go, once I can get a decent image.

As an aside, in my DSO images I am struggling to bring out the ‘typical’ red hue associated with star forming regions in galactic spiral arms. Would your suggestion work here, ie use the Compose module to ‘add’ a dedicated red channel and combine it?

Just a thought.

Thanks again - much appreciated. I am so grateful for the advice and for Ivo in developing this tool and selling it for next to nothing.

Clear skies
Matt

[admin]

Hi Matt,

There is a false color palette, specifically for solar imaging.
You can access it in the Color module via the Matrix parameter (choose "False Color: Solar").
It should yield a yellow starting point, but you can use the bias sliders to change the hue (e.g. reducing the green bias slider will maker the yellow less prevalent and bring out reds).

E.g. you'd transform something like this;

Sun_g.jpg (167.46 KiB) Viewed 16165 times

Into this;

sun_c.jpg (200.22 KiB) Viewed 16165 times

Hope that helps!

[admin]

As an aside, in my DSO images I am struggling to bring out the ‘typical’ red hue associated with star forming regions in galactic spiral arms. Would your suggestion work here, ie use the Compose module to ‘add’ a dedicated red channel and combine it?

For this you'd use the NBAccent module (assuming you'd like to accent visual spectrum data with Ha detail, correct?)