Post Processing...

[Stellaraya]

Hi everyone,

I Decided to try and take some photos of the milky way and subtract dark frame from it (first time). However the more dark frames I subtract the greener the image got and nothing I did corrected this without making the photo in my opinion unusable. what am I doing wrong? :shrug:


Any advice would be great...
Stellaraya

[rustigsmed]

Hi Stellaraya,

Which program are you using? Are you using Deep Sky Stacker?

Cheers

Rusty

[Stellaraya]

I use Gimp only for post processing...

[rustigsmed]

I haven't used gimp, but maybe someone on here can help.
Have you tried to realign the RGB channels after the dark frame subtraction?

[Stellaraya]

Ahh what? LOL I've done nothing to the dark frames what so ever.

Can you please explain what I have to do?

[rustigsmed]

it might more useful if you post the image up so people can have a look and give some advice :)

[ZeroID]

Stellaraya, Dark frames are used during the processing of stacked images in astro programs like Deep Sky Stacker which use them to eliminate hot pixels and the like.
Would help if you posted an image and explained better how you are trying to process your images. More information needed please.

[Stellaraya]

Id post one if it wasn't like 2.5Mb in size, working on reducing it but for now.. I'm loading the Light frame into gimp then opening the dark frame as a layer then selecting Subtract in the mode and reducing opacity to about 50-60%. Using one frame makes it slightly green using two or more makes it a sickly green that is hard to correct.

[rustigsmed]

you can resize in paint, or post a link to a site like flickr.

[Stellaraya]

Thanks, So here it is...

[multiweb]

Your dark subtraction is fine. The green cast is probably due to the milkyway being lower on the horizon. That's quite natural. There's a utility called Hasta la vista green (HLVG) which will remove green gradients from your pics. See repro attached.

[Stellaraya]

Does Gimp have that feature? I like how you kept the colours in the band

[multiweb]

Not sure about Gimp but PixInsight does. It's SCNR I think.