Drizzle and dual ba...
 
Share:
Notifications
Clear all

Drizzle and dual band filters


(@ennui2342)
White Dwarf Customer
Joined: 3 years ago
Posts: 17
Topic starter  

I've been experimenting with drizzle on data from an l-extreme filter with some interesting results which I thought I'd share. In the attached picture of the jellyfish nebula the left integration is using the Ha-OIII color algorithm with normal drizzle. I've noticed when I do this (not just in this case) that I get this kind of basket weave texture in high magnification. The middle integration is switching to using Bayer/X-trans drizzle - surprising how much better this is - great result!

Where I get a bit lost is with trying to break out Ha and OIII whilst drizzling. The third pane is Ha-OIII extract Ha algorithm with Bayer/X-trans drizzle. Although the tooltip says the algorithm should be ignored in this case, you can see it actually isn't and is producing a grayscale image but it's not clear to me what's actually happening. It looks like there's bayering artefacts remaining in the image, and I don't think it is Ha - if I switch to extract OIII it looks like the same output. Ideally what I'd like is the quality of the Bayer/X-trans drizzle with the ability to separate out the Ha and OIII data. It seems I have to choose between bayer/X-trans drizzle with Ha-OIII color or normal drizzle with Ha-OIII extract - have I understood this right, or missed some way of doing this?

I should just add that extracting the two channels has really made a massive difference to my processing workflow and results. Thanks very much for adding this capability, it's highly valuable!

-Mark

image

ReplyQuote
Topic Tags
(@ennui2342)
White Dwarf Customer
Joined: 3 years ago
Posts: 17
Topic starter  

I see there is a fix for this in yesterdays release - I'll grab it and give it a go! Thanks.

-Mark


ReplyQuote
(@vincent-mod)
Quasar Admin
Joined: 5 years ago
Posts: 4736
 

Sorry for being late, but this may indeed be the bug you encountered and is fixed. Hope it does the trick!


ReplyQuote
(@mabula-admin)
Quasar Admin
Joined: 5 years ago
Posts: 3122
 
Posted by: @ennui2342

I see there is a fix for this in yesterdays release - I'll grab it and give it a go! Thanks.

-Mark

Indeed Mark, This is from the detailed release notes 😉

https://www.astropixelprocessor.com/community/release-information/astro-pixel-processor-1-083-preparing-next-release/

  • FIXED, BAYER DRIZZLE WITH THE HA-OIII debayer algorithms, enabling bayer drizzle with the Ha-OIII extract Ha or extract OIII algorithms did not work correctly. It showed the exact same result which was similar to the Ha-OIII mono debayer algorithm. It now works correctly as is show in the next screenshots:

Bayer Drizzle with Ha-OIII mono (so mix of the Ha and OIII signals):

BayerDrizzle HaO3 mono

Bayer Drizzle with Ha-OIII extract Ha (only Ha):

BayerDrizzle HaO3 extractHa

Bayer Drizzle with Ha-OIII extract OIII (only OIII):

BayerDrizzle HaO3 extractO3

A HOO composite of these Ha and O3 signals made with the RGB Combine and Selective Color tools (data courtesy of Ian Barredo @tracer, asi533 Optolong L-Extreme filter):

HOO custom cbg SC St

 

 


ReplyQuote
(@ennui2342)
White Dwarf Customer
Joined: 3 years ago
Posts: 17
Topic starter  

Mixed results so far... It definitely is now pulling out the signals properly, whereas before they looked the same no matter the algorithm, now it's clear the Ha and OIII are being extracted. However I'm seeing some banding on OIII and mono, while the Ha and color look great. Left to right is color, mono, OIII, Ha.

-Mark

image

 


ReplyQuote
(@mabula-admin)
Quasar Admin
Joined: 5 years ago
Posts: 3122
 

Dear Mark @ennui2342,

Thank you, glad to see that the signals are as expected for Ha & OIII.

Please be aware of the requirement for using Drizzle in general:

  1. You need a lot of data, many frames !
  2. They need to be undersampled
  3. And all the frame need to be well dithered

 

What you are describing as banding, are well-known drizzle artefacts in fact. It means that not all pixels in the target drizzle grid are receiving enough data... leading to artefacts.

So it is very likely that you don't meet the drizzle requirements in your data with the drizzle settings that you used.

As a first step, enlarge the drizzle droplet size, then probably the drizzle artefacts reduce and the result will be less noisy as well 😉

Assuming you did dither you data with a random dither (so in all directions), how large was the dither step between exposures?

Which drizzle settings did you use for droplet, scale and kernel?

And how many frames were your processing with what kind of setup and exposure time?

Mabula

This post was modified 5 months ago 4 times by Mabula-Admin

ReplyQuote
(@ennui2342)
White Dwarf Customer
Joined: 3 years ago
Posts: 17
Topic starter  

@mabula-admin Thanks for the advice, I'll give that a go - haven't played with the drizzle settings at all because its a 2hr integration 🙂 I just automatically assumed it was something I had done wrong because it only was showing on the OIII rather than a lack of undersampling.

The data is 237 300s frames on a Redcat with an ASI533mc which gives a scale of 3.1 arcs/pixel, dithering every 2 frames by 5 pixels. I used 0.5 droplet, with 2 scale and tophatkernel.

-Mark


ReplyQuote
(@ennui2342)
White Dwarf Customer
Joined: 3 years ago
Posts: 17
Topic starter  

I should add that the reason I'm drizzling is because by eye the stars do look undersampled and blocky. On the right is a normal integration with no drizzle, on the left is the Bayer drizzle. Fantastic results for the color image.

-Mark

image

 


ReplyQuote
(@mabula-admin)
Quasar Admin
Joined: 5 years ago
Posts: 3122
 
Posted by: @ennui2342

@mabula-admin Thanks for the advice, I'll give that a go - haven't played with the drizzle settings at all because its a 2hr integration 🙂 I just automatically assumed it was something I had done wrong because it only was showing on the OIII rather than a lack of undersampling.

The data is 237 300s frames on a Redcat with an ASI533mc which gives a scale of 3.1 arcs/pixel, dithering every 2 frames by 5 pixels. I used 0.5 droplet, with 2 scale and tophatkernel.

-Mark

Since it is Bayer Drizzle, you need to be aware that with droplets of only 0.5 you need a massive amount of data..., much more than you process now. This is because the bayer holes really are not well covered quickly. So try droplets of 1.0 and keep scale just at 1.0 to start with 😉

What you can do to find nice drizzle settings for any particular set is to use the Composition Crop mode in 6) Integrate. You can then simply test the drizzle settings an a small interesting part of your field of view 😉 Then when you have nice settings, giving you a fine balance between noise and sharpness and no drizzle artefacts, apply those settings on the full composition. Oh, keep the default kernel as well. Don't use the point kernel with Bayer Drizzle.

Let me know if this helps.


ReplyQuote
(@ennui2342)
White Dwarf Customer
Joined: 3 years ago
Posts: 17
Topic starter  

Why did I not spot the composition crop! That will certainly help with experimentation. I'll let you know how it goes, thanks Mabula.

-Mark


ReplyQuote
(@mabula-admin)
Quasar Admin
Joined: 5 years ago
Posts: 3122
 
Posted by: @ennui2342

I should add that the reason I'm drizzling is because by eye the stars do look undersampled and blocky. On the right is a normal integration with no drizzle, on the left is the Bayer drizzle. Fantastic results for the color image.

-Mark

image

 

Indeed 🙂 Okay try droplets of 1.0 with scale 2.0 and let me know if the artefacts dissapear and the stars still look good ;-). It will definitely be less noisy. The smaller the droplets, the noisier is will be and more sharp. This is what drizzle will do, you need to find a balance to your liking between noise and sharpness.

Mabula

 


ReplyQuote
(@ennui2342)
White Dwarf Customer
Joined: 3 years ago
Posts: 17
Topic starter  

The crop tip sped things up a lot, thanks Mabula, though still took quite a while to experiment as it takes a long time to load in file mappers for that many images (is there any way to reuse the file mapping between runs?). I read up a bit and now understand why I was having the problems with the bayer drizzle. I would suggest tweaking the pop-up that encourages switching from drizzle to bayer drizzle for CFA data - it implies this is a like for like swap rather than the fact that your settings will likely also need changing.

I had trouble finding any settings with this data that I was happy with for the bayer drizzle. By the time the patterns were more under control the stars had returned to blockiness. In the end I settled instead on debayering first plus standard drizzle at drop size 1 and scale 2 for the Ha and OIII - It's not as sharp as the bayer drizzle, but the fixed patterns are down to an acceptable level. For the colour integration I ended up doing a bayer drizzle with the same settings which seemed to cope better. 

The screengrab shows the following: top row left to right is OIII drizzle, colour no drizzle, Ha drizzle; bottom row is colour bayer drizzle, colour drizzle, and no drizzle just scale 2.

I have to say I still can't get my head around why the OIII has worse patterns than the Ha - I'm assuming the Ha is from the red pixels and OIII from blue and green so I would have expected OIII to have more data to work with and fewer holes to cover. Maybe I don't understand the algorithm you're using to break out Ha and OIII data from the RGB? I'm also puzzled why the colour data is better - technically there's still the same holes to cover, so shouldn't it show the same fixed patterns in each colour that I see when I break out Ha and OIII, or is the overlaying of the fixed patterns canceling out into something that looks like random noise? One other thing to note is that the colour drizzle seems to have better colour than the colour bayer drizzle which has a greenish cast - assume this is because of double the green pixels in the CFA seeping through.

Thanks for all your help - I thought I understood this after reading your great forum post on drizzle, but it turned out I didn't until I read some more 🙂 I'm happy with where I've got to now and in the end I'm being really picky at very high magnification here which is not going to make any visible difference to the final result. It's good to know what's going on behind the settings though!

-Mark

image
This post was modified 5 months ago by ennui2342

ReplyQuote
(@mabula-admin)
Quasar Admin
Joined: 5 years ago
Posts: 3122
 

Hi @ennui2342,

The crop tip sped things up a lot

Excellent 🙂 I will have a look at the tooltip, maybe it will be easier if I internally use 2x droplet size when Bayer Drizzle is enabled? then you can use same droplet size with Bayer and Bayer Drizzle and better compare it? I will think about it

I had trouble finding any settings with this data that I was happy with for the bayer drizzle. By the time the patterns were more under control the stars had returned to blockiness. In the end I settled instead on debayering first plus standard drizzle at drop size 1 and scale 2 for the Ha and OIII - It's not as sharp as the bayer drizzle, but the fixed patterns are down to an acceptable level. For the colour integration I ended up doing a bayer drizzle with the same settings which seemed to cope better.

Yes, okay.

I have to say I still can't get my head around why the OIII has worse patterns than the Ha - I'm assuming the Ha is from the red pixels and OIII from blue and green so I would have expected OIII to have more data to work with and fewer holes to cover. Maybe I don't understand the algorithm you're using to break out Ha and OIII data from the RGB? I'm also puzzled why the colour data is better - technically there's still the same holes to cover, so shouldn't it show the same fixed patterns in each colour that I see when I break out Ha and OIII, or is the overlaying of the fixed patterns canceling out into something that looks like random noise? One other thing to note is that the colour drizzle seems to have better colour than the colour bayer drizzle which has a greenish cast - assume this is because of double the green pixels in the CFA seeping through.

Yes, the green cast in Bayer Drizzle is definitely produced by having 2x green pixels over red and blue. It is clear that the amount of information in R & B suffers relative to green and so you get a green cast. Much more data would remedy that for the color bayer drizzle using the same drizzle settings.

I think the O3 will have much less signal in general versus the Ha data, leading to more problems?

I the end, you would like to make a Ha O3 bi-color composite, right? So I would not concern myself with the Ha O3 color result. I would focus on getting nice Ha + O3 stacks and then make a nice bi-color, it wiil look much better than the color result where normally Ha will dominate over O3, thus seeing little of the O3 contribution.

Mabula

 


ReplyQuote
(@bjoernh)
Molecular Cloud Customer
Joined: 1 year ago
Posts: 4
 

Hi there!

I have a very similar problem as  ennui2342 with the same setup: Redcat, ASI533mc-pro and a Optolong l-enhance dual narrowband filter in my case. I have nearly 8 hours worth of data (130x 3min), drizzled every third frame by max 5 pixels randomly in both axes. When I try to use bayer drizzle, these artifacts appear. It doesn't matter if droplets are anywhere between 1.2 to 2 and scale at 1 or >1 leads to similar results, with different appearances of these artifacts. They become very prominent once the scale is above 1. They always have a frequency of 3 pixels, no matter what scale I use.

Attached first image HA, second image OIII extract.

Any ideas how to fix this?

HA Bayer Drizzle
OIII Bayer Drizzle

ReplyQuote
(@ennui2342)
White Dwarf Customer
Joined: 3 years ago
Posts: 17
Topic starter  

Glad to hear it isn't just me doing something silly Björn! I tried many different setting combinations and just couldn't get this to work, after 22 hours of data captured on the same target the o3 and mono integrations were still awful and I gave up and resorted to separating the channels post integration using pixinsight pixelmath rather than doing the separation in APP. The HaO3 colour integration is excellent so this gives a good result, even though I'd prefer to do the separation in APP with x-trans as it should be higher quality!

-Mark


ReplyQuote
(@mabula-admin)
Quasar Admin
Joined: 5 years ago
Posts: 3122
 

Hi @bjoernh & @ennui2342,

I have never experienced this myself to be honest with my data, so it might be still a problem with the data or the dither steps being too small. A dither of max 5 pixels is really small in my experience. Are your dither steps really random? If not, it could explain this ugly repeating pattern in your dither results.

I can not exclude that there might be an issue with Bayer Drizzle in combination with these Ha-O3 extract formula, so probably it is good if one of you or both can share your data with me so I can test and exclude some problem of APP's processing here 😉

Please upload it using the instructions at the top right of the forum and let me know once uploaded.

Mabula


ReplyQuote
Share: