cybereye wrote:I separated my image into it's 3 components but found the green channel generation in the LRGB module to be a tad too strong. How does the green channel get created?
The green channel is created by averaging the blue and red channels, which is the same as layering red on top of blue with an opacity (or 'Blend Amount' in ST) of 50%.
With my playing around, and with some searching on the web, the best method I've found for creating the green channel is to layer the blue over the red channel in GIMP/PS and set the blue layer to "multiply" rather than "normal". The resultant doesn't seem to be as strong as either the blue or the red channels but gives a fairly pleasant result when all 3 are recombined.
As I have an OSC I need to separate my channels in PS (GIMP doesn't handle 16bit tif files although I have a 2.9 version to try...). This is not easy to do. Does StarTools have the capability for you to separate the 3 channels, ditch the green and then synthesis it using the multiply method I mentioned previously in this post?
I never heard of this method before, but ST can certainly do this. The LRGB module, when confronted with a colour image, extracts the relevant channel (e.g. if you click 'Red' and load a colour image, the LRGB module will only extract the red channel from that colour file). Using this, you can extract the relevant channels from a colour file.
So, to create a multiplication of the two channels;
Launch LRGB, click red, load image, red channel will be extracted, Keep (we're not interested in Tracking right now, so I just indicated the image has been stretched to get Tracking off my back
).
Launch LRGB, click blue, load image, blue channel will be extracted, Keep (again, we're not interested in Tracking right now).
Launch Layer module, 'Fill mask', click 'Undo > Bg' or 'Undo > Fg' to copy the undo buffer (which will contain the red data) into the foreground or background (doesn't matter for multiply operation). Set 'Layer Mode' to 'Multiply'. That's your new green channel. Click 'Keep', Save your new green channel.
Now to you simply use the LRGB module again to load R and B from the original image and load the new green channel we just made as G.
This option, I believe, would be a great help to we "Urban Astrophotographers" who use LP filters... well it would to me at least!!
I'd love to see your results as, to be quite honest, I doubt it would yield anything close to a correct colour. If you do go this route, however, I would use a synthetic luminance frame as well, so that your exposure time in the green channel doesn't go to waste. In this case, you can simply click the 'L' button and load the original image as the luminance file. The LRGB module will automatically average all the channels and create a luminance frame out of them.
There is one other thing you could do though to attain correct star colours; simply image without an LP filter for your RGB (colour) data, and use a blend (depending on exposure time) of the LP filtered data + non-LP filtered data as your luminance data. It may seem a bit tricky at first, but once you got the hang of it it should yield the best of both worlds in your situation.
You are looking for a method to create a synthetic green channel from narrowband data (not RGB data). In that case any talk about the 'correct' color balance is moot and the description in this document may well work to your satisfaction. What does stil stand though is my suggestion for an RGB solution in the face of the light pollution you're experiencing!