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WIERD!!


Rodd

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I am flabbergasted.  This was collected with Televue np 101is and STT-8300.  I have never been able to render as nice an image as I would like from this data--a whopping 30 hours ( 10 each of Ha, SII, and OIII).  Here is the Ha stack compared to an individua; sub.  My eyes may be deceived, but I think the sub looks better than the 10 hour stack.  It makes no sense.  I checked all the subs and they are fine--I certainly have used worse in an image.  These images have not been processed at all--just a screen stretch using the STF tool in PI.  This makes no sense to me.  No wonder I have not been satisfied with my many attempts.  Any ideas?  

 

Single sub

1119459761_Ha30minsub.thumb.jpg.af5187eab6d966a6e511205446953f5b.jpg

10 Hour stack

133208205_Ha2030minsubs.thumb.jpg.2d518dc2f045e40bed8eea6d057b13f4.jpg

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There really can be no answer from us looking at two JPEGs. If you are doing long subs in excellent conditions - then, as you see, a bunch of them will not pull out  too much more detail. You will get a better SNR with the stack but if there is not too much noise in the single sub.....well there is only so much that stacking will do with that too. Only to be expected I think........but each target will be different.

I have often planned many hours of subs on targets only to stop at half my planned amount - simply because I knew many more hours would not make a huge difference. Now, (you may have noticed from my posts), I test what I have from time to time....after 3 hours of data; after 5 hours of data.....whenever it is convenient to have a look (and not at any set points). Sometimes it is just not worth getting  say 10 + 10 + 10 hours of SHO.....but you may find your time is better spent with e.g 8 hours Ha + 12 hours SII + 10 hours OIII.....or whatever....depending on the signal from the object you are shooting.

I don't necessarily agree that the single sub here is clearer and deeper. You say you have just done STF. The stacked image I would imagine will lend itself better able to be processed than the single sub....I am sure the fine detail is there to be drawn out. Just perhaps it is a fact....that you did not need 10 hours of subs to get it!

Have fun and enjoy the journey. Perhaps it will be clear again for me tonight (I have 3 different images needing more data)....but in the meantime I have lots of work to do in the garden!

Edited by Kinch
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Not weird at all.

You are relying on STF to provide you with same level of stretch - and it is not happening.

Stacked data is lacking contrast due to different level of stretch and that does not look nice. If you really want to see the difference - you need to do "split screen" approach. Copy half of still linear single sub data and paste it over still linear stack (have them aligned of course so they form proper image after copy/paste operation).

Then proceed with any stretching / processing. This will make obvious difference for given level of processing as both sides of the image will undergo same processing.

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2 hours ago, vlaiv said:

Not weird at all.

You are relying on STF to provide you with same level of stretch - and it is not happening.

Stacked data is lacking contrast due to different level of stretch and that does not look nice. If you really want to see the difference - you need to do "split screen" approach. Copy half of still linear single sub data and paste it over still linear stack (have them aligned of course so they form proper image after copy/paste operation).

Then proceed with any stretching / processing. This will make obvious difference for given level of processing as both sides of the image will undergo same processing.

Well since I have processed a couple hundred images and this is the only time this has happened....yes, wierd.  That is what the stud is for, to show you an approximation of what the image will look like with a generic stretch.  Never before has a single sub looked brighter and revealed more details at normal viewing scales than a stack of subs.  In this case 10 hours.  So yes, wierd.  Most of the time the faint regions are not even visible in the single sub.  Not in this case.  

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3 hours ago, Kinch said:

There really can be no answer from us looking at two JPEGs. If you are doing long subs in excellent conditions - then, as you see, a bunch of them will not pull out  too much more detail. You will get a better SNR with the stack but if there is not too much noise in the single sub.....well there is only so much that stacking will do with that too. Only to be expected I think........but each target will be different.

I have often planned many hours of subs on targets only to stop at half my planned amount - simply because I knew many more hours would not make a huge difference. Now, (you may have noticed from my posts), I test what I have from time to time....after 3 hours of data; after 5 hours of data.....whenever it is convenient to have a look (and not at any set points). Sometimes it is just not worth getting  say 10 + 10 + 10 hours of SHO.....but you may find your time is better spent with e.g 8 hours Ha + 12 hours SII + 10 hours OIII.....or whatever....depending on the signal from the object you are shooting.

I don't necessarily agree that the single sub here is clearer and deeper. You say you have just done STF. The stacked image I would imagine will lend itself better able to be processed than the single sub....I am sure the fine detail is there to be drawn out. Just perhaps it is a fact....that you did not need 10 hours of subs to get it!

Have fun and enjoy the journey. Perhaps it will be clear again for me tonight (I have 3 different images needing more data)....but in the meantime I have lots of work to do in the garden!

This is one sub Brendan

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4 minutes ago, Rodd said:

Well since I have processed a couple hundred images and this is the only time this has happened....yes, wierd.  That is what the stud is for, to show you an approximation of what the image will look like with a generic stretch.  Never before has a single sub looked brighter and revealed more details at normal viewing scales than a stack of subs.  In this case 10 hours.  So yes, wierd.  Most of the time the faint regions are not even visible in the single sub.  Not in this case.  

Why don't you just try what I suggested to see if it will make any difference to your perception of quality of each image?

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1 minute ago, david_taurus83 said:

Not that you need telling, as your images are stunning, but have you tried processing just the Ha stack? Did you take any subs under moonlight? It does look a bit softer than the single sub but also very clean of noise.

I have long ago.  I thought I would revisit. Each attempt leaves me unsettled and I had forgotten why.  You know you bring up a good point.  But other times when I throw inferior signal strength subs into the mix they do not soften the image, they just impart less brightness.   When I check, a stack with a few dimmed subs still has a higher SNR than a stack without them.  Of course, if a sub is totally black or clouded out that is different

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great images.... Im so interested in this subject because i just cant see the advantage of a ten hour integration over a 5 hour. ive never seen enough detail change in my own final stack to continue shooting for ten hours when i can do two targets at 5 hours each. just my opinion. I tend to do 6 hours max over a few days if im doing HARGB. if its a single osc shot ill do 4 hours total.

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1 hour ago, vlaiv said:

Why don't you just try what I suggested to see if it will make any difference to your perception of quality of each image?

I will later when I get home.  O700 here now.  Off to work.  Regardless, every time I integrate a bunch of subs the stack is ALWAYS better than a single sub by a very wide margin using stf.    Most of the time dimmer regions are not visible in the single stack, except for this time.  If you stub your toe and turn sound to look and there is nothing there, what will you believe, the fact that there is nothing there do you could not have stubbed your toe, or the blood pooling beneath your foot

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33 minutes ago, Dan13 said:

great images.... Im so interested in this subject because i just cant see the advantage of a ten hour integration over a 5 hour. ive never seen enough detail change in my own final stack to continue shooting for ten hours when i can do two targets at 5 hours each. just my opinion. I tend to do 6 hours max over a few days if im doing HARGB. if its a single osc shot ill do 4 hours total.

Your right--when you are right--sometimes 10 is needed sometimes 5 is needed.  But this is 1 sub

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1 hour ago, vlaiv said:

Why don't you just try what I suggested to see if it will make any difference to your perception of quality of each image?

Well--thats also my point....it should not take that type of effort to see the difference between 10 hours and 30 min--especially since the 30 min is 1 sub. 

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36 minutes ago, Rodd said:

Well--thats also my point....it should not take that type of effort to see the difference between 10 hours and 30 min--especially since the 30 min is 1 sub. 

Not really, or rather - it depends.

We have to be pragmatic about this and understand what is going on.

I'll try simple analogy and then connect that with real world example in imaging.

Consider this (I just realize that this may involve more mental gymnastics than I initially envisaged since we are used to different temperature units - but try to convert to F what I say in C) -

Difference between half an hour and 10 hours is x20. That is sqrt(20) = ~x4.5 improvement in SNR.

Now consider the difference between water that is at body temperature and one that is x4.5 colder - or about ~ 8.2C.

There will be wast difference in sensation between the two. Splash 37C water on someone and they wont get too excited - maybe a bit annoyed because they are wet now. Do that with 8.2C water and it is likely that they will jump from their seat - it will feel rather cold.

Drink a glass of water on one temperature and other and you will see very big difference. Swim in water with said temperatures and difference will be huge.

Now, consider 8.2C and 1.82C water or maybe even between 1.82C and 0.4C. Both are very cold, both are near freezing but we don't ascribe big difference between those temperatures - but they are still x4.5 ratio in value.

 

You know that for each additional imaging time - SNR improves like square root of time spent. If you want to double SNR, you need to spend x4 imaging time on target. At some point you enter region of diminishing returns since we can't tell difference between 50 and 100 SNR but we can tell difference between 5 SNR and 10 SNR. Notice that both are x2 improved.

If I do this:

Stack.gif.9aa1079faab0fe85f11607d93799413f.gif

Everyone will see the obvious difference between the two:

- Stack is lacking hot pixels and cosmic ray artifacts

- Stack is much much smother - all the grain is no longer there (SNR is indeed improved adequately for x20 longer exposure)

- Images are stretched differently and stack lacks contrast - it is much "flatter"

Everything seems to be as one would expect for high signal target and half an hour vs 10 hour of exposure (except the difference in stretch).

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6 minutes ago, vlaiv said:

Stack is lacking hot pixels and cosmic ray artifacts

- Stack is much much smother - all the grain is no longer there (SNR is indeed improved adequately for x20 longer exposure)

- Images are stretched differently and stack lacks contrast - it is much "flatter"

Everything seems to be as one would expect for high signal target and half an hour vs 10 hour of exposure (except the difference in stretch

I totally disagree with the contention.  First of all.....Fahrenheit and Celcius?  My brain is not ready for that.  More importantly, in the above example, the single sub is MUCH better than the stack--yes the stack does not have as much noise or cosmic rays--but the details in the single sub are much sharper and deeper (you can see more details).  No question.  The stack is terrible to my eyes.  Garbage.  I won';t even process it.  The single sub shows promise, the stack looks terrible.  You are not supposed to have to process a stack to make it look like a single sub--the opposite is true.   If you honestly believe this is normal.....I'd say you are blinded by theory and are not looking at the images.

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Id go back over your stacking parameters and try again and see if you get the same result, maybe something was off.

Ive just separated your images and put one on each of my dual monitors, IMO i can tell which one is the 10 hour stack by doing this and now think the stack is better but marginally. This goes back to my previous post, i dont believe IMO 10 hours data on a single target is justified compared to say 5 hours.

In this case it still is strange because your single sub is very close to that of a stacked image, but then again with a 30 min sub i think your at the limit of getting the most detail you will from that target in any given shot. by taking 19 more your really only fine tuning the detail lines and not the whole nebula.

Stacked image is cleaner -less distorted/less noise-more detailed , not sure what else your after here....

 

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6 minutes ago, Dan13 said:

Id go back over your stacking parameters and try again and see if you get the same result, maybe something was off.

Ive just separated your images and put one on each of my dual monitors, IMO i can tell which one is the 10 hour stack by doing this and now think the stack is better but marginally. This goes back to my previous post, i dont believe IMO 10 hours data on a single target is justified compared to say 5 hours.

In this case it still is strange because your single sub is very close to that of a stacked image, but then again with a 30 min sub i think your at the limit of getting the most detail you will from that target in any given shot. by taking 19 more your really only fine tuning the detail lines and not the whole nebula.

Stacked image is cleaner -less distorted/less noise-more detailed , not sure what else your after here....

 

The stack sucks---I won't even process it.   The level of detail visible in the single sub is MUCH more than the stack.  details completely disappear in the stack!!!   1 30 min Ha channel is not enough to produce the type of images I like to produce at least not in my sky.  You keep saying 5 hours vs 10.  This is 1/2 hour.  Not the same.

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Just now, Rodd said:

The stack sucks---I won't even process it.   The level of detail visible in the single sub is MUCH more than the stack.  details completely disappear in the stack!!!   1 30 min Ha channel is not enough to produce the type of images I like to produce at least not in my sky.  You keep saying 5 hours vs 10.  This is 1/2 hour.  Not the same.

Your missing my point, Maybe its my fault. I joined the topic to discuss the advantages/disadvantages of 10 hours integration or 5 hours. i think 10 is over kill and wont benefit any more...thats just my findings.

with regards to your issue, i dont believe the single frame is better when inspecting it differently, i think the stack is.

Try and re process, its the only option. Its near impossible for a single sub frame to be better then a final stack so maybe your processing was off.

then stack half the data (5 hours) and compare that to you ten hours. Id say you will save yourself 5 hours sleep after seeing the results.

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2 minutes ago, Dan13 said:

Your missing my point, Maybe its my fault. I joined the topic to discuss the advantages/disadvantages of 10 hours integration or 5 hours. i think 10 is over kill and wont benefit any more...thats just my findings.

with regards to your issue, i dont believe the single frame is better when inspecting it differently, i think the stack is.

Try and re process, its the only option. Its near impossible for a single sub frame to be better then a final stack so maybe your processing was off.

then stack half the data (5 hours) and compare that to you ten hours. Id say you will save yourself 5 hours sleep after seeing the results.

As I said before--your point depends on the target, the focal ratio one is shooting with and the sky.  As far as the single sub above and the stack--there is absolutely no question in Vlad's demonstration that teh stack is much less detailed than the single sub.   Just look at the dark structure.  It is sharp and well formed in the sub and almost invisible in the stack.   For me, that sub is excellent and I would be (and was) eleated to get it when I did.  The stack is tosh, as they say.........If you think the stack is better, you must like images that are totally smeared with noise suppression.  Becuase that is what it looks like--the dark structure is gone.  NOT the way 5, 10, or 20 sub stacks are supposed to look compared to a single sub used in those stacks

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Tbh Rodd, Your attitude towards @vlaiv earlier and now myself is uncalled for.

You dont want to take any advice or info on board , you sound like you know best so i would advise to continue as you were and do you.

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2 minutes ago, Dan13 said:

Tbh Rodd, Your attitude towards @vlaiv earlier and now myself is uncalled for.

You dont want to take any advice or info on board , you sound like you know best so i would advise to continue as you were and do you.

Truth hurts.   Instead of trying to see slights and attitude in written words--why not just concentrate on the staements made?.  I guess you are so perfect that no one should disagree with you.  Just look at the images and stop worrying about attitude that is not there.   I never asked for advise....we are discussing the sub and stack.  I asked for an analysis--one that I dissagree with.  Sorry.

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28 minutes ago, Rodd said:

As far as the single sub above and the stack--there is absolutely no question in Vlad's demonstration that teh stack is much less detailed than the single sub.   Just look at the dark structure.  It is sharp and well formed in the sub and almost invisible in the stack.

 

2 minutes ago, Rodd said:

Truth hurts.   Instead of trying to see slights and attitude in written words--why not just concentrate on the staements made?.  I guess you are so perfect that no one should disagree with you.  Just look at the images and stop worrying about attitude that is not there.   I never asked for advise....we are discussing the sub and stack.  I asked for an analysis--one that I dissagree with.  Sorry.

I agree with all that you've said - no much point in going back and forth saying the same. This is why I proposed you do "split image" approach.

I'm trying to explain to you that level of contrast and how much dark structures stand out - depends on contrast and level of stretch. STF did not apply same level of stretch on both images - it is algorithm that examines noise and some other features and then calculates some level of stretch. It does not mean it is best stretch to show what is in the image.

Given that stack and single sub have different levels of noise - STF will stretch them differently. In order to compare them - one needs same level of stretch - and possibly simplest way to do it is to make single image out of two halves while still linear and then stretch such image. It is guaranteed to have same level of stretch and will show differences easily.

Alternatively - post stack and single sub and I'll gladly combine them for you and upload still linear result - for you to stretch to your liking as well as demonstration stretch done by me.

In the mean time, what do you think about this:

 

Stack2.gif.3429026103b882a380a7e5011d6baccc.gif

Which version do you prefer now?

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5 minutes ago, vlaiv said:

Which version do you prefer now?

Obviously the stack.....but, regardless of the processing that went into it, my point was normally, when I integrate my subs I use the STF the way it was meant to be used--so you can see the image and make decisions about cropping, and where to place the DBE points, and well, you know.  That is why screen stretches are valuable...essential actually unless one likes working blind.  This is my point....in every other instance...bar none, the STF screen stretch of the newly integrated stack ALWAYS looks superior to the STF screen stretch of an individual sub.   Everything you have said may be right....but it doesn't change the fact that this is an unusual, hence "wierd" occurrence.  I did process this data and it came out OK--over processed as was my won't 2 years ago, but yes, the stack CAN be made to look better than the single sub.  Can you imagine how much better if the stack started out looking better instead of blurry and faint?

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