Pixinsight drizzle woes.

[Anthonyexmouth]

Does drizzle in PI mess with the colour?

Got a fairly nice M31 image yesterday, added more data last night and thought I'd drizzle as im borderline undersampled. I've tried this in the past and always makes processing difficult for me. Is it my shortcomings or is this a quirk of drizzle?

 

[Anthonyexmouth]

Heres the image. One with drizzle the other without. same calibration frames and subs. 

Cant for the life of me get the same nice colour as I get with the non drizzle version? Or is the drizzle version a better colour? WDYT?

 

No Drizzle

 

Drizzle

[Stuart1971]

First of all why are you drizzling…? Are you well undersampled…?? 
I actually prefer the non drizzle version, as much more structure detail showing…👍🏻

[Anthonyexmouth]

Just now, Stuart1971 said:

First of all why are you drizzling…? Are you well undersampled…?? 
I actually prefer the non drizzle version, as much more structure detail showing…👍🏻

I much prefer the non drizzled one, but why can't I replicate it with the drizzle?

Astronomy tools says i'm slightly undersampled

[vlaiv]

17 minutes ago, Anthonyexmouth said:

Astronomy tools says i'm slightly undersampled

I would not trust it.

What is FWHM of your stack (in either pixels or arc seconds)?

[Anthonyexmouth]

10 minutes ago, vlaiv said:

I would not trust it.

What is FWHM of your stack (in either pixels or arc seconds)?

Drizzle 4.2

Non-Drizzle 2.2

the stack itself ranged from 1.2 to 2.0

 

That's according to subframe selector in PI. 

[vlaiv]

24 minutes ago, Anthonyexmouth said:

Drizzle 4.2

Non-Drizzle 2.2

the stack itself ranged from 1.2 to 2.0

 

That's according to subframe selector in PI. 

That is in pixels right?

You are then right where you want to be (maybe a bit over sampled actually ) - if your FWHM is 1.6px - then you are properly sampled. If it is less than that, you are under sampled - higher than that and you are starting to get into over sampled territory.

Don't bother with drizzle, but do see about that color. It does look better in drizzled version (not sure what the reason is).

[Anthonyexmouth]

3 minutes ago, vlaiv said:

That is in pixels right?

You are then right where you want to be (maybe a bit over sampled actually ) - if your FWHM is 1.6px - then you are properly sampled. If it is less than that, you are under sampled - higher than that and you are starting to get into over sampled territory.

Don't bother with drizzle, but do see about that color. It does look better in drizzled version (not sure what the reason is).

The drizzle (bottom) looks better? 

I thought the non drizzle was less muddy looking. 

Astronomy tools gives me this. 

 

[vlaiv]

11 minutes ago, Anthonyexmouth said:

Astronomy tools gives me this. 

I'm aware of what astronomy tools gives, and I think it is completely wrong.

I started a thread with explanations as to why it is wrong and giving much more accurate account of the whole thing (with background info and sources) but nothing was really done to remedy that and apparently many members disagree with me (or facts, not sure how to put it):

 

16 minutes ago, Anthonyexmouth said:

The drizzle (bottom) looks better? 

I was not referring to image itself, but color information in image - it does look better, or rather more accurate.

Non drizzled version seems to have teal tone to it, with reddish dust lanes and reddish/white core.

Drizzled version looks much more realistic in terms of color - central part of galaxy mainly contains yellow stars and should be therefore yellow. There is a bit more of hot young stars in spiral arms that are light blue. Dust lanes are brown.

All match what is expected in such galaxy.

 

[Anthonyexmouth]

18 minutes ago, vlaiv said:

I'm aware of what astronomy tools gives, and I think it is completely wrong.

I started a thread with explanations as to why it is wrong and giving much more accurate account of the whole thing (with background info and sources) but nothing was really done to remedy that and apparently many members disagree with me (or facts, not sure how to put it):

 

I was not referring to image itself, but color information in image - it does look better, or rather more accurate.

Non drizzled version seems to have teal tone to it, with reddish dust lanes and reddish/white core.

Drizzled version looks much more realistic in terms of color - central part of galaxy mainly contains yellow stars and should be therefore yellow. There is a bit more of hot young stars in spiral arms that are light blue. Dust lanes are brown.

All match what is expected in such galaxy.

 

Ah ok, so probably, the colour is down to my processing skills or lack of at the moment 

If my fwhm is hovering between 1.2 and 2 on my subs I should or shouldn't worry about drizzle?

[vlaiv]

12 minutes ago, Anthonyexmouth said:

Ah ok, so probably, the colour is down to my processing skills or lack of at the moment 

If my fwhm is hovering between 1.2 and 2 on my subs I should or shouldn't worry about drizzle?

Yes, you are properly sampled and nothing to be gained by drizzle.

[Anthonyexmouth]

Just now, vlaiv said:

Yes, you are properly sampled and nothing to be gained by drizzle.

Thanks. That'll save some time and disk space. 

[Stuart1971]

Anything under 3.0”/pixel does not really benefit that much from drizzle, in my limited experience….👍🏻