Ha from 20th April

[Freddie]

Captured on 20th April with the usual FireCapture, AS3!, ImPPG and PS

Now to make a start on the high res WL

[Altocumulus]

Stunning!

[neil phillips]

I am no expert on Ha. Still learning about white light. But looks great on my 4k monitor. Smooth and detailed 

[TakMan]

That’s lovely Freddie…

Could I trouble you for some acquisition and also processing details please…. If you are prepared to share..?

I’d be interested to know how many frames you stack from your total and the sort of settings you use in AS!3 (size of alignment points and quantity) as I’m new to that version… I’ve been using the setting where it adds multiple sized points over each other - running into the 4-5 thousand - which takes ages on the wife’s Ryzen 5 laptop (can’t get AS!3 to work under WINE on my Mac).

Will be keeping this as a reference shot for my own data!

Damian

[Freddie]

Thanks for the comments guys. Much appreciated.

I'll gather my thoughts and post up some notes on capture and processing later.

[Freddie]

8 hours ago, TakMan said:

That’s lovely Freddie…

Could I trouble you for some acquisition and also processing details please…. If you are prepared to share..?

I’d be interested to know how many frames you stack from your total and the sort of settings you use in AS!3 (size of alignment points and quantity) as I’m new to that version… I’ve been using the setting where it adds multiple sized points over each other - running into the 4-5 thousand - which takes ages on the wife’s Ryzen 5 laptop (can’t get AS!3 to work under WINE on my Mac).

Will be keeping this as a reference shot for my own data!

Damian

For me, the key is that daytime seeing is rubbish so you need to do everything possible to overcome that. Having a go at WL imaging is good to get your eye in as it is so much harder than Ha.

One thing that isn’t lacking in solar is signal given the sun is so bright so I set gain as low as possible i.e. very low single digit to keep the noise down. Some would say that you need some gain to reduce read noise but my real world experience is that gain may reduce read noise but the overall addition of noise with gain swamps the reduction in read noise, so low gain for me. I also leave gamma well alone. I believe you said in a recent post that you were adjusting gamma during capture. The problem with that is that the data is lost for ever that way but if you leave gamma alone during capture you can always make adjustments in post processing. I aim for a histo about 60% which for me means an exposure of about 2ms.

The point of the low gain and hence noise is that it allows me to keep the number of frames in the stack as low as possible. I would never go above 100 and often use as few as 50. Given the seeing is usually so bad, having only a few frames in the stack keeps the image sharp. I use alignment size 56 typically which gives around 1,000 alignment points and have not seen any benefits from multi.

I then take the stack into ImPPG and try not to go too mad on the sharpening. Using only the absolute best frames means that it shouldn’t need much sharpening anyway. It’s then into PS where I adjust the overall brightness with levels. Take care with the black point as it is easy to lose detail in the umbra by setting the black point too high which just turns the whole umbra region black. I then use curves to add contrast to the whole image but again keep an eye on the umbra. You can protect the detail in the umbra by pinning the curve at the bottom or by using a layer for the umbra and a layer for the rest of the surface. I never use any noise reduction. For me, if you have to use noise reduction, it just means you have been too aggressive in ImPPG sharpening.

I have no doubt that others will use different methods to great effect and may disagree with my approach but this is what I do for what it’s worth.

 

[neil phillips]

17 hours ago, Freddie said:

For me, the key is that daytime seeing is rubbish so you need to do everything possible to overcome that. Having a go at WL imaging is good to get your eye in as it is so much harder than Ha.

One thing that isn’t lacking in solar is signal given the sun is so bright so I set gain as low as possible i.e. very low single digit to keep the noise down. Some would say that you need some gain to reduce read noise but my real world experience is that gain may reduce read noise but the overall addition of noise with gain swamps the reduction in read noise, so low gain for me. I also leave gamma well alone. I believe you said in a recent post that you were adjusting gamma during capture. The problem with that is that the data is lost for ever that way but if you leave gamma alone during capture you can always make adjustments in post processing. I aim for a histo about 60% which for me means an exposure of about 2ms.

The point of the low gain and hence noise is that it allows me to keep the number of frames in the stack as low as possible. I would never go above 100 and often use as few as 50. Given the seeing is usually so bad, having only a few frames in the stack keeps the image sharp. I use alignment size 56 typically which gives around 1,000 alignment points and have not seen any benefits from multi.

I then take the stack into ImPPG and try not to go too mad on the sharpening. Using only the absolute best frames means that it shouldn’t need much sharpening anyway. It’s then into PS where I adjust the overall brightness with levels. Take care with the black point as it is easy to lose detail in the umbra by setting the black point too high which just turns the whole umbra region black. I then use curves to add contrast to the whole image but again keep an eye on the umbra. You can protect the detail in the umbra by pinning the curve at the bottom or by using a layer for the umbra and a layer for the rest of the surface. I never use any noise reduction. For me, if you have to use noise reduction, it just means you have been too aggressive in ImPPG sharpening.

I have no doubt that others will use different methods to great effect and may disagree with my approach but this is what I do for what it’s worth.

 

I have seen some lunar done recently at high elevation. with a large  Cassegrain. The approach was similar. With a longer exposure And very low gain. ( the result was stunning) Though with a lot more frames used. But the point is, i also believe gain produces grain, the higher and higher its used. It comes out, and is very noticeable via sharpening. Is less tolerant to sharpening.

That's not to say i do everything with low gain. ( Saturn at 10") wouldn't work well. But there are occasions when the target is bright as you suggest that lower gain can be used effectively. And as you say lower noise needs less frames. As good as AS/3 is some bad frames will often get through.  New to white light as you know Freddie. But i think your logic is sound. Totally agree about black points. A lot of subtle detail is lost when taken too far. The slight grey appearance to some may seem wrong. But with a jet black Umbra all subtle detail is squashed. I see it a lot. Glad to see someone with as much experience in the field as you coming to similar conclusions. Your results show your technique working well. Though i will say under the worst seeing shorter exposures definitley have there place

 

[Freddie]

Thanks Neil. In terms of exposure, I agree that short exposures help in poorer seeing conditions if your can reduce from a reasonably long exposure but my experience is that when you are already down at 2ms, reducing it really doesn't make any difference.

[neil phillips]

50 minutes ago, Freddie said:

Thanks Neil. In terms of exposure, I agree that short exposures help in poorer seeing conditions if your can reduce from a reasonably long exposure but my experience is that when you are already down at 2ms, reducing it really doesn't make any difference.

Diminishing returns at those exposures i guess. 

[Pete Presland]

Very nicely captured

[TakMan]

Hi Freddie

Thanks for the reply and apologies for the lateness of my acknowledgment.

I'm not an experienced solar (or deep sky) imager, yet I'm interested in learning 'best practise' and find it fascinating the different approaches to get the best results/most out of a given system.

Firstly, can I ask, do you use any aperture mask for your AR152, or run it at the native f/6.5 ?

OK, to your reply!

On 28/04/2022 at 23:14, Freddie said:

you said in a recent post that you were adjusting gamma during capture

Correct, well sort of! I usually keep Gamma at neutral (1), so 'off' and modify that later in Photoshop if I wish as part of my own process. I always thought that was the 'right' way to do things.
I did attempt a few tests though last time out, reducing Gamma between 0.7-0.9 for some Proms and increasing Gamma up to 1.3 for disk images to add a bit more density/contrast.
This was after reading the new 'Solar Astronomy' book published by Axilone (edited by Christian Viladrich - who is an experienced imager over on SolarChat). Specifically for my camera (Basler aca1920-155), he suggested that his testing showed the camera applied any Gamma setting before the analog to digital conversion which had no effect on quantisation noise - Page 318), so could be a legitimate tool for capture.
I'm still going through my own data and think I will stick to a neutral Gamma setting at acquisition (although I can't see anything wrong with the data captured with Gamma modified) and just adjust Gamma to help locate prominences and achieve focus.

On 28/04/2022 at 23:14, Freddie said:

Some would say that you need some gain to reduce read noise but my real world experience is that gain may reduce read noise but the overall addition of noise with gain swamps the reduction in read noise, so low gain for me

I'm definitely going to have to try your method next time out!
I went the other way....
If using Mono12 I have Gain right up around 18.5 db and with Mono8 it's 30.5 db (db is now Basler's own Pylon software sets it - I'm on Mac and Phyon is the only software that supports the camera... although I am looking at a Windows gaming laptop to move to Firecapture at some stage).

These gain figures are not arbitrary but were settled on after loads of testing (well I ran the tests and processing in ImageJ and @vlaiv - of course!) did the data analysis to find the lowest noise for each using documentation from Basler and cross reference with the ZWO174 that uses the same chip.

I actually find Mono12 to produce cleaner data. There is less noise (and less vertical chip structure) in the dark 'space' regions when imaging proms. The offset is that Mono12 only runs to 110fps, produces larger files and require longer exposures (9-12ms).

Mono8 runs at 2-3ms and hits the full 165fps.

But., unlike your findings:

On 28/04/2022 at 23:14, Freddie said:

The point of the low gain and hence noise is that it allows me to keep the number of frames in the stack as low as possible. I would never go above 100 and often use as few as 50. Given the seeing is usually so bad, having only a few frames in the stack keeps the image sharp.

I need a minimum of 150-200 frames to stack in Mono12 to suppress the noise (usually choose 250-300) and 300-500 in Mono8. I felt I was on the right track as I capture 3-4000 frames in a 22-30 second capture run (so 10-15% chosen to stack) and then later read the same in the Solar Astro book "300 to 600 images for Ha disk images and 300 to 900 images for Ha prominences" - page 332...

I was also aiming for filling the histogram up to 80%, but have found this can clip the bright regions!

Having read (and re-read) your reply, I will definitely have to give your method a go. Perhaps I'll drop the gain down to a point where I can still capture at 2-5ms and take it from there (perhaps 5-10ms under better seeing).

I presume you use flats to remove any non-uniformity of your Quark..? Do you use BIAS (or dark frames) to calibrate the flats and/or the light frames...?

Lastly, I posted a few RAW data sets saved out of AS!3 over on my original thread. Could I trouble you (when/if) you have time to take a look - I'd be very interested to see your take on processing my data!

Enjoy the rest or your Bank Holiday, clear skies...

Damian

Edited May 1, 2022 by TakMan

[vlaiv]

Excellent image!

Things regarding noise levels are quite straight forward, although @neil phillips and myself already had discussion along those lines and did not reach the same conclusion.

Gain affects read noise in modern CMOS cameras in known way - usually there is a graph published for each camera, and one can easily measure their camera for read noise levels at different gain settings. Result is - read noise goes down with higher gain.

Gain does not directly affect any other type of noise. This is where Neil and myself had disagreement before. Freddie also seems to be sharing Neil's opinion on this - but that is not based on theory (nor experiment for that matter). Higher gain won't produce noisier results.

What can happen is that higher gain will produce noisier results if one exposes for histogram rather than for time. This is how higher gain can indirectly affect noise levels.

However - this is what I always caution people not to do - expose for histogram. Primary factor with lucky type / planetary imaging is to expose just enough to freeze the seeing. This is usually 5-6ms or less - depending on actual seeing at that moment. It is also related to aperture size and Fried parameter. It is also related to Greenwood frequency.

https://en.wikipedia.org/wiki/Greenwood_frequency

Coherence time is inverse of this frequency:

Quote

There are various ways to define the Greenwood frequency, but all the definitions attempt to represent the frequency at which the turbulence distortion of the image is changing. The reciprocal of the Greenwood frequency is sometimes known as the Greenwood or atmospheric time constant (τ₀). Since the distortions are approximately constant over a period less than this time constant, adapting the optical system at a faster rate yields negligible benefits; conversely, adaptive system performance degrades significantly as the response speed decreases below the Greenwood value, since that means that the distortions are changing faster than the system can adapt.

Freezing the seeing means just that - time period in which distortion is not changing. If we integrate for longer period of time and atmospheric distortion is changing during this time - we will capture both distortion and motion blur of this change. We want to avoid later and select frames with minimal distortion.

Once we have selected our exposure time - then rule is rather simple:

Increase gain until you are near of hitting saturation (you want to avoid saturation).

Different types of planetary imaging mean different brightness of the target - Solar Ha and Lunar probably being the brightest and here you don't have to raise gain much as you will have plenty of signal to start with and chance is that you will saturate pretty quickly if you up the gain.

Not sure what are usual signal levels with Ha (after all, it is pretty restrictive filter on its own), but for planetary where planets are much dimmer - one can go very high with gain on short exposures without saturation.

Keep in mind that it is bad to lower exposure time just to be able to raise the gain. This is counter productive as at those signal levels, shot noise is much higher than read noise. It only makes sense to raise the gain in order to lower read noise - once your exposure time is fixed. With fixed time - you have fixed shot noise as you have fixed signal levels. It only makes sense to lower read noise then without changing shot noise.

Also note that lowering exposure time less than coherence time will not yield sharper results - atmosphere is already frozen. If coherence time is 5ms and you expose for 2 seconds - you will get two frames with same distortion. Overall - you will have equal percentage of good/bad frames. You will have more frames - but total integration will be the same, and as far as SNR goes - best SNR for same total integration time is one that is consisting out of the least number of subs (that means the subs are longer and each sub already has higher SNR).

 

[Freddie]

Thanks for your comments everyone. Appreciated.

Damian, full 152mm at all times for me. Only calibration I use is flats. Taken out of focus on a bland area of the surface.

Vlaiv, thanks for your full explanation of the theory on this. Over the years that I have been imaging at high resolution in Ha and WL my real life experience of having tested various settings is that my low gain low stack count approach produces the best quality images.

Maybe there are just too many variables at play to just rely on theory rather than practical experience for solar imaging and I know Neil produces absolute top quality planetary images so I’ll be sticking with low gain for now. Always open to improve things though so if you can show some of your own high resolution Ha and WL images (particularly high resolution WL as that is my main interest in solar) that show the improved quality of your theory I would be very interested.

Edit: A thought whilst I was eating my dinner. Maybe we should be talking about settings that produce the best final image rather than specifically gain producing noise? I guess it is possible that increased gain doesn’t produce increased noise when noise is defined by the strict scientific term. What I do know though is that increased gain produces a lower quality final image because of something that looks like noise and that was the point of the discussion. So rather than hold back any future discussion about the effects of gain by referring to noise, we should just be discussing in terms of gain resulting in poorer quality images and therefore low gain is advantageous, be it because of actual as per the scientific term noise or just something that appears in the image at higher gain that looks like noise and you can’t just rely on theory, you have to get out in the field (or back garden in my case) Just a thought as I guess in the imaging section we are all just trying to produce the best images we can.

And for those that are wondering, it was roast chicken!!!!

Edited May 1, 2022 by Freddie

[vlaiv]

1 hour ago, Freddie said:

Maybe there are just too many variables at play to just rely on theory rather than practical experience for solar imaging and I know Neil produces absolute top quality planetary images so I’ll be sticking with low gain for now. Always open to improve things though so if you can show some of your own high resolution Ha and WL images (particularly high resolution WL as that is my main interest in solar) that show the improved quality of your theory I would be very interested.

It's not my theory, it is well established theory on how light and sensors work and well established theory of lucky imaging.

I'm not going to try to convince you that what I'm saying is right, after all, I'm just repeating what are well established facts. If you wish - we can run simple experiment that will show that increased gain does not mean increased noise - actual noise measured will in fact be somewhat less due to decrease in read noise (but otherwise shot noise does not depend on gain settings).

On the other hand, if you don't want to change anything in your work flow, then of course don't, after all, as above image shows, it's producing excellent results.

There is only one slight issue with recommending your workflow to people. It is based on anecdotal evidence - it works for you, under your circumstances. Theory works in all instances (where it is applicable), and it will work for everyone if properly applied. If it does not - then it is flawed and should be replaced with more accurate theory. So far we have not yet seen evidence that theory is flawed.

 

[Freddie]

Thanks for the comments Vlaiv and I wouldn’t want to try and convince you that you are wrong. All I know from my hands on experience of actually producing images is that the theory is all well and good sitting inside at a keyboard but when it comes to actually producing images, experimentation over the years has shown that increased gain, ends up with poorer quality images. Maybe you have produced some actual solar images that you can post up that show the opposite.

[vlaiv]

14 minutes ago, Freddie said:

experimentation over the years has shown that increased gain, ends up with poorer quality images.

Does this hold for increased gain while keeping exposure length the same?

[neil phillips]

6 minutes ago, vlaiv said:

Does this hold for increased gain while keeping exposure length the same?

A question Vlaiv. so in your opinion setting gain at say 80 on lunar. where read noise is higher than with higher gain settings with a ASI 290. Is not optimal ? is that correct ?

 

[vlaiv]

3 minutes ago, neil phillips said:

A question Vlaiv. so in your opinion setting gain at say 80 on lunar. where read noise is higher than with higher gain settings with a ASI 290. Is not optimal ? is that correct ?

 

Not the matter of opinion - higher gain settings for same exposure length and same number of stacked subs will produce less noisy image.

This is what math is telling us.

Only difference between two stacks - one with higher gain and one with gain 80, if exposure length is the same and of course same camera is used under same conditions - is amount of read noise. All other noise sources will be the same and signal will be the same.

Gain 80 stack will have more read noise than higher gain stack and everything else will be the same - hence Gain 80 stack will have lower SNR.

 

[neil phillips]

3 minutes ago, vlaiv said:

Not the matter of opinion - higher gain settings for same exposure length and same number of stacked subs will produce less noisy image.

This is what math is telling us.

Only difference between two stacks - one with higher gain and one with gain 80, if exposure length is the same and of course same camera is used under same conditions - is amount of read noise. All other noise sources will be the same and signal will be the same.

Gain 80 stack will have more read noise than higher gain stack and everything else will be the same - hence Gain 80 stack will have lower SNR.

 

So  gain at 80 with more read noise is not optimal is that correct ?

[vlaiv]

14 minutes ago, neil phillips said:

So  gain at 80 with more read noise is not optimal is that correct ?

I would not use term optimal for single variable, but yes, having everything else the same, gain of 80 will produce stack with worse SNR than higher gain that has less read noise.

[neil phillips]

14 minutes ago, vlaiv said:

I would not use term optimal for single variable, but yes, having everything else the same, gain of 80 will produce stack with worse SNR than higher gain that has less read noise.

Ok just wanted your opinion as i know of other world class lunar imagers that seem to want images with worse SNR According to you.

 Even though they have invested in much time and effort with high elevation and large 19" optics. What you dont seem to realize or consider is such read noise is completely swamped out at the 15ms being used. So here the theory and math of read noise does not tell the whole picture. And can be in some situations as highlighted here. Completely misleading 

Edited May 1, 2022 by neil phillips

[neil phillips]

Anyway its good to talk. But we cant all agree all of the time. So i will continue to take a broad look at settings from many different people (including you)  and my own results. 

And use what i think is giving me the best results. But certainly worth trying many different settings to see the effects they have. And the results they bring. I have listened to what you say and tried to use that information on occasion on my own imaging. All information is useful. 

[Freddie]

56 minutes ago, vlaiv said:

Does this hold for increased gain while keeping exposure length the same?

Yes.

As I said earlier though, maybe the talk of increased gain and increased noise isn’t helping in this discussion. You may well be right that increased gain doesn’t increase noise (that being noise by the true scientific definition) but as an imager I don’t really care about the theory of gain and noise, what I care about is what it takes in reality to produce the best quality images and I know from actually being out there trying different settings, getting the data and producing images is that increasing gain (even at the same exposure) produces poorer quality images because of something that looks like noise.

The discussion about the theory of this is all very interesting but I would still be keen to see your solar images that show that increased gain doesn’t produce a poorer quality image in an actual image rather than a theoretical one. Maybe in addition to this imaging section we need a new section where people can post theoretical images 😀

[neil phillips]

34 minutes ago, Freddie said:

Yes.

As I said earlier though, maybe the talk of increased gain and increased noise isn’t helping in this discussion. You may well be right that increased gain doesn’t increase noise (that being noise by the true scientific definition) but as an imager I don’t really care about the theory of gain and noise, what I care about is what it takes in reality to produce the best quality images and I know from actually being out there trying different settings, getting the data and producing images is that increasing gain (even at the same exposure) produces poorer quality images because of something that looks like noise.

The discussion about the theory of this is all very interesting but I would still be keen to see your solar images that show that increased gain doesn’t produce a poorer quality image in an actual image rather than a theoretical one. Maybe in addition to this imaging section we need a new section where people can post theoretical images 😀

Your probably right. Especially as Vlaiv is so adamant. Perhaps i shouldn't term it noise. But when it looks like a duck and quacks like a duck. its hard not to think i am seeing ducks. 

 

[vlaiv]

51 minutes ago, neil phillips said:

Ok just wanted your opinion as i know of other world class lunar imagers that seem to want images with worse SNR According to you.

 Even though they have invested in much time and effort with high elevation and large 19" optics. What you dont seem to realize or consider is such read noise is completely swamped out at the 15ms being used. So here the theory and math of read noise does not tell the whole picture. And can be in some situations as highlighted here. Completely misleading 

That is exactly one of the things I wanted to point out.

Sure that person in question knows that they can swamp read noise in 15ms exposures at high altitude at the site of good seeing. I just wander if that person ever recommended someone starting in lunar AP - to necessarily use 15ms as it produces excellent results for them?

Anecdotal evidence can sometimes be misleading. In average seeing, even with 8" aperture you can't really hope to have coherence time longer than say 5-6ms, let alone 15ms. Just imagine for a second that person reading advice is interested in Ha solar with internal etalon with scope that operates at F/30 while using ASI290.

That is oversampling by x3.4. Now we have x3 less exposure time and pixel is 3.4 x 3.4 = 11.56 smaller by surface than it needs to be, which makes about x35 lower signal in total. Do you still think that signal will significantly swamp read noise?

There is no harm in my advice - only benefit. While this benefit might be marginal for some setups - it is always correct and for some people it will make a difference.

40 minutes ago, Freddie said:

The discussion about the theory of this is all very interesting but I would still be keen to see your solar images that show that increased gain doesn’t produce a poorer quality image in an actual image rather than a theoretical one. Maybe in addition to this imaging section we need a new section where people can post theoretical images

It will be as full as imaging section dedicated to images taken with equipment and processed with software backed by science and theory not so easily dismissed by people using them.

Edited May 1, 2022 by vlaiv