combining non-linear narrowband data

[alistairsam]

hi,

I processed individual stacks in ha,o3,s2 as they had different gradients,
I want to combine them in the HST palette, but when I open them in the compose module, choose non-linear and don't activate tracking, I see only one channel in the colour module.
how do I combine stretched channels in the compose module?

Thanks
Alistair

[Carles]

Just an idea,

try doing Wipe to each file, but without stretching. It should keep the linear state. Save each wiped file
then use compose module to load the files already wiped

See if that works

Carles.

[admin]

hi,

I processed individual stacks in ha,o3,s2 as they had different gradients,
I want to combine them in the HST palette, but when I open them in the compose module, choose non-linear and don't activate tracking, I see only one channel in the colour module.
how do I combine stretched channels in the compose module?

Thanks
Alistair

Hi Alistair,

I am a little confused what you are trying to do ?

Processing stacks separately is not recommended for a number of different reasons. You do not need to remove gradients from the stack separately - Wipe will handle this (as matter of fact, it will handle this in the luminance and chrominance domain separately for even better results).

how do I combine stretched channels in the compose module?

Combining differently stretched channels does not make sense - your coloring will contain artifacts and suggest emission concentrations that do not exist. If that is what you are trying to do, then please don't do this - it is not sound documentary photography.

Combining channels that are still linear are less objectionable (but if they have been meddled with in the linear domain, noise will be worse). But if that is the that case, why are you avoiding activating Tracking?

That said, if you really must combine stretched channels for whatever reason, you can do so by setting Luminance, Color to "RGB, RGB (Legacy)".

Finally, gradients in narrowband data are fairly rare, as most unwanted signal never makes it past the respective filter. Are you sure it's not some issue with your flats?

Hope this helps,

[alistairsam]

hi

thanks for the replies, only reason I was processing them individually and then trying to combine was to remove gradients in each separately.
I will try and compose them as linear images and wipe.

I'm trying to create a narrowband image of the horsehead and have around 18 hrs of ha,s2,O3 but can't seem to arrive at a pleasing colour palette with HSO. as Ha is dominant, its overly green. can I adjust the ratio of the green channel to red and blue?
Also, instead of a synthetic Luminance, can I use just Ha as luminance or is there a better approach?

thanks
Alistair

[admin]

I'm trying to create a narrowband image of the horsehead and have around 18 hrs of ha,s2,O3 but can't seem to arrive at a pleasing colour palette with HSO. as Ha is dominant, its overly green. can I adjust the ratio of the green channel to red and blue?

In StarTools, uniquely, color is processed entirely independently of your luminance/detail. So, indeed, once you hit the Color module towards the end of your workflow you can change the coloring to your heart's content. The green dominance of Ha is not an issue and has not bearing at all on the coloring. You can even completely remap the channels after the fact. So if, instead of the default SHO palette, you wanted a HSO palette, or wanted different mixes of narrowband for the channels, then you can do that with impunity without having to start all over again. Narrowband processing in StarTools is extremely powerful.

You can see all this in action in this demonstration by your truly, where I process a SHO dataset which - indeed - shows that Ha dominance, as is expected in most cases.

Also, instead of a synthetic Luminance, can I use just Ha as luminance or is there a better approach?

You can use Ha as luminance only, sure; simply set the exposure time for the other datasets to 0. However, if the S-II and O-III is otherwise reliable (e.g. the "gradients" are not uneven lighting issues instead) and originate from the same camera, then you should really be able to add them to your Ha for a better (more comprehensive) signal.

Do you know what caused the gradients?

[RICH-DSO]

load them (tiff or jpg) as stretched and use the layer module...