Author Topic: Recipes for Bi-Color HA OIII of NGC 7000?  (Read 627 times)

Offline bvalente

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Recipes for Bi-Color HA OIII of NGC 7000?
« on: 2019 July 31 09:31:09 »
I would love to see some examples of bi-color processing for HA and OIII for my finished data?

what recipe do you use to create a narrowband bi-color RGB image? My recipes never seem to look very good, i'm hoping to get some insights here.

These are registered and cropped .xisf masters of HA and OIII so they are ready to go (although i haven't done anything like linear fit, just registration)

HA https://www.dropbox.com/s/ola8rw1avl9f4o0/NGC%207000%20HA%20master.xisf?dl=0
OIII https://www.dropbox.com/s/0chm3btjdbw13ba/NGC%207000%20OIII%20master.xisf?dl=0

Thanks!

Brian


Offline pfile

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Re: Recipes for Bi-Color HA OIII of NGC 7000?
« Reply #1 on: 2019 July 31 10:26:03 »
i think the Ha image suffers from bad flattening; there is a strong bright circular large-scale artifact there. you should probably resolve that before trying to process the image.

rob

Offline bvalente

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Re: Recipes for Bi-Color HA OIII of NGC 7000?
« Reply #2 on: 2019 July 31 10:27:52 »
Rob that's fair feedback thanks. Unfortunately the bigger fix won't be happening anytime soon. i found out the filter wheel i have did not set the filters accurately so there is some amount of mis-registration for the flats. and btw, that is for the last 18 months of data.

i can fix that as part of DBE short term, I'm replacing that filter wheel with a higher quality one, but in the meantime, i got what I got :) :(

Right now i'm primarily interested in recipes for color combination, knowing the corners won't be the greatest

Offline pfile

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Re: Recipes for Bi-Color HA OIII of NGC 7000?
« Reply #3 on: 2019 July 31 10:54:37 »
ok, well even with DBE it's hard since there is so much signal where you're trying to extract the background.

have you tried straight HOO or maybe HO (0.2*H+0.8*O) ?

rob

Offline bvalente

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Re: Recipes for Bi-Color HA OIII of NGC 7000?
« Reply #4 on: 2019 July 31 11:04:22 »
Rob i agree it's a tough call for DBE - and why i'm swapping out that hardware

on your recipe HO (0.2*H+0.8*O)

are you suggesting blue = 0.2*H+0.8*O?

Thanks again

Brian

Offline pfile

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Re: Recipes for Bi-Color HA OIII of NGC 7000?
« Reply #5 on: 2019 July 31 11:28:34 »
yes, the idea is that where there is Ha at strength 1, there is Hb at strength 0.2-0.3; Hb is deep blue. however of course atmospheric extinction means that you wouldn't necessarily see that exact proportion if you had an Hb filter... so it's kind of fudged. the 0.8*OIII is because @ 496um, the OIII signal is 100% green and about 75% blue. you might experiment with that proportion as well.

you will get different results depending on whether or not you have linear fit the OIII to the Ha. while there is no physical basis for linear fitting them, the combination may look better as usually the Ha signal totally dominates the OIII and in the combination you don't really see the OIII at all if they are not linear fit. since it's a narrowband image, you might as well do what you think looks best...

rob






Offline bvalente

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Re: Recipes for Bi-Color HA OIII of NGC 7000?
« Reply #6 on: 2019 July 31 11:35:28 »
Here is
HOO
https://www.dropbox.com/s/yq13wa7wps68y0n/NGC7000_HOO.jpg?dl=0

and 
HO(0.2HA + 0.8OII)
https://www.dropbox.com/s/4oj6krjokylblef/NGC7000_HO_Hx0.2_Ox0.8.jpg?dl=0


There's no miracle to this combination process, just the above. linear fit didn't seem to do much but I can also monkey with some other processing like curves. I don't know - the color doesn't look very good to me.

Maybe i'm just comparing to others that include SII and i just need to get on with collecting that data, like
https://apod.nasa.gov/apod/ap161011.html


Thanks

Brian

Offline pfile

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Re: Recipes for Bi-Color HA OIII of NGC 7000?
« Reply #7 on: 2019 July 31 11:45:30 »
yeah bicolor is sometimes rough. it's true that SHO images are way more interesting color-wise and look much better.

i think in your processed images the gradient is still messing things up. i suppose you could use ColorMask to get a green mask and then tweak the green a little bit so it looks more blue. but processing this data is really difficult...

rob

Offline bvalente

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Re: Recipes for Bi-Color HA OIII of NGC 7000?
« Reply #8 on: 2019 July 31 11:50:59 »
Thanks Rob

so when you say processing this data is really difficult, are you primarily concerned with the gradient, or equally concerned there is no SII?

It's one challenge to gather more data, it's another challenge to say the data i have is not very workable


Brian

Offline pfile

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Re: Recipes for Bi-Color HA OIII of NGC 7000?
« Reply #9 on: 2019 July 31 12:16:30 »
well i was trying to say that (i assume) you have done DBE to the masters for those jpegs, but i can still see the gradient hanging around. so i think that limits what you can do with the data color-wise, since reds that aren't really there start becoming dominant when you push the saturation, etc.

maybe its worth a try with ABE to see how it solves the gradient.

rob

Offline pfile

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Re: Recipes for Bi-Color HA OIII of NGC 7000?
« Reply #10 on: 2019 July 31 23:19:59 »
i found that using axial symmetry in the Ha image helped extract the gradient a little better.

i also did an HOO mapping without stars (using starnet++).

there's a zipfile attached with a dynamic crop icon and a dbe icon for the Ha. however, it is on a workspace named "tulip" and i'm not sure what PI will do when you load that since most likely you don't have a workspace with that name.

rob



Offline bvalente

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Re: Recipes for Bi-Color HA OIII of NGC 7000?
« Reply #11 on: 2019 August 01 07:55:27 »
That's fantastic Rob, beautiful image. Thank you for including the icons,

i'll study up!

Thank you again, so much

Brian