lock042

@Spaced Out: a positive answer could help all the community :).

On 14/02/2024 at 15:14, Spaced Out said:

Brilliant ! Thanks. I thought I did but nothing happened. Just restarted and tried it again tho and it has worked ! However, it produced this 🤔 , I'm guessing there is a setting somewhere that I need to work out.

 

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Hello @Spaced Out. As indicated in the topic, you need to check the dither option. If you made a stack with Siril, in 32bits mode, you wouldn't have needed it, though.

In order to improve the documentation, could you send me your stack output image (WeTransfer), and give me the rights to use it for the Siril documentation?

Yes this is allowed.

Siril is free, open source, under the GPL3 license terms.

Please update. This behavior will disappear.

5 minutes ago, vlaiv said:

Flats correct light pollution as well

 

Ok. Sorry but I stop here. This assertion is so wrong that I couldn't go further.

Have a nice day.

40 minutes ago, vlaiv said:

If one is shooting in very light polluted area - background sky signal can be quite high. You are correcting this background sky signal with variations in flats. It will create some variation in corrected background signal - more signal there is, greater variation will be in absolute value.

We are talking about removing dark flat to flats. We don't care about light pollution.

This is my whole point. We are just talking about flats here.

Of course darks are very important to remove all unwanted signal to light frames.

9 hours ago, jjosefsen said:

I don't think you can say that synthetic bias works for all flats < 5 sec. I have an ASI1600 clone and I have amp glow in 1,8s darkflats.. 🤔

 

Be careful. Your ampglow can be negligeable at 1.8s, like with 294MM. If you look your image very stretched, of course you will see it, but statistics don't lie.

4 minutes ago, markse68 said:

What is the degree order setting in background extraction for? Does increasing this make it better for non linear background removal?

Everything is explained here: https://siril.org/tutorials/tuto-manual/#background-extraction

16 minutes ago, GalaxyGael said:

I think Siril is great overall, but the background removal takes several tries for those in severe light poll. gradients like me, I find. APP still is the most effective imo in that regard. 

 

Did you tried to remove background on each sub? It works pretty well.

16 minutes ago, GalaxyGael said:

But, does anyone know how to use monochrome flats in siril?

Siril works only with monochrome or CFA flats. 

11 minutes ago, vlaiv said:

It seems that I need to use command line and cd command to change working directory to where I want it to be. That is good enough - but not quite intuitive

To change working directory you can use the "home" button at the top.

2 minutes ago, vlaiv said:

Destination box won't let me type path like D:\my_folder\test_sequence

Try relative path. I know it works in script mode. 

On 20/12/2021 at 18:01, bruno said:

HI Does anyone know how to reduce the size of the screen in Siril as it is too big for the screen and i can't see any of the buttons (pressing the minimise button doesn't help & also when i open the Colour calibration panel for it to do a plate solve and get the colours the OK button is hidden out of site  so i can't use it i would have to do a calibration manually.

Thank for any info Bruno

Could you send a screenshot please? 

Symlink do work with windows development mode on. 

But conversion does not change pixel value. 

23 hours ago, vlaiv said:

I don't want to hijack the thread, but title is rather convenient for what I'm about to ask.

Is there a way to tell Siril not to mess with ADU values when stacking? I don't want them to be scaled to 0-1 or 0-65535 range, I want them to be kept as they are.

Uncheck the "normalize output" button. 

14 hours ago, vlaiv said:

If that is the case, can you run simple test for me with ASI294, just to confirm?

Take two bias subs.

On one of those, subtract offset and then analyze it for standard deviation (measure of noise). Then take again first sub and subtract second from it and again analyze it with standard deviation to compare which approach produces noisier result.

OK, what you were asking for before is not the test you have been doing, as nowhere in your procedure you were asking to subtract a master.

What I gather from your experiment is that:

• First line is the stats of a single bias

• Second line is the stats of same bias with a constant value subtracted

• Last line is the stats of same bias – a masterbias.

Fair enough, it makes “more sense”. At least if the discussion from the start had been about calibrating biases… which is not at all the point.

So here is the test that we have been talking about. Made 200 darkflats of 0.9s, matching the flats done for a session from last summer. ZWO ASI294MC, gain 120, offset 30, T -10C for reference.

Stacked 1, 10, 25, 50, 100, 150 and 200. Yes, of course, the std decrease with increasing subs…

Then checked the stats of a flat (1^st CFA channel only, it would not make sense on a color sensor to measure all channels altogether) from which I have substracted a synthetic offset of 1920 and masterdarkflats made with 50, 100, 200 stacked frames respectively.

And here-below the results:

I’m not even going to claim that there is significant reduction in noise in the calibrated flat, because the stds are probably within the uncertainties. But to be honest, this kind of measure is the basis for questioning the usefulness of using darkflats (or bias) to calibrate the flats.

I hope this will encourage others to test with their setup.

So now I think we've done enough testing (here and with the post). We're not forcing anyone to adopt synthetic bias, but we've shown in different ways that it's worth a try.

2 minutes ago, vlaiv said:

do your bias files have 0 stddev to begin with?

Of course not and this is why subtracting master bias or master dark flat adds noise, because they have noise. And this is why subtracting synthetic bias (i.e a constant) don't.

I think you don't get the point at all.

14 minutes ago, vlaiv said:

If that is the case, can you run simple test for me with ASI294, just to confirm?

 

I'm sorry but this is signal processing basics.
With image operations, even with subtraction, the noise is added in the result, even with a master dark flat of 100 images. In the case of the synthetic bias you only use a constant. So noise stays the same.
So ok, difference is not huge with a master containing a lot of frame. But why would you add noise, even if it is not too much.

2 minutes ago, alacant said:

OK. So I loaded the master bias:

right click -> statistics

 Does this look OK?

Sure. And as DSLR use power of 2 you can take 2048 as constant (you even can enter this value in the preferences : =2048).

This is the value I use with my DSLR.

2 minutes ago, alacant said:

@lock042 maybe you could describe your 'how to make a synthetic bias' implementation in simple terms (without spreadsheets!) for those of us here who take the pragmatic approach to imaging? Or maybe a list of bias settings for popular cameras so we can simply type in the required values into Siril?

With DSLR it is very simple.

Take your master offset you did used. Measure the median value and it will be your level.

27 minutes ago, vlaiv said:

Can you explain how synthetic bias produces less noise?

By not adding noise at all.

Subtracting image adds noise. Subtracting level don't.

Another test from Christian Buil (famous French astronomer which as created IRIS): http://www.astrosurf.com/buil/asi294mm.html

Comment. The offset signal is so uniform that I recommend for processing to equate it to an image of constant level: a synthetic bias, so the constant level is equal to the average (or better, median) intensity of a typical offset taken with the settings selected (gain, offset, temperature). This initiative is one way to reduce processing noise.

Thanks a lot @clouzot for your tests that perfectly match ours.

That shows that we are trying to say. Make your own tests with your setup, and I bet that in most cases you will find no differences. (Oh wait, maybe less noise  )

You say than ampglow has different ADU values. But take a look at the figure we did: the plot is inside the AG area on purpose!!. These differences are negligible in comparison to the flat. They mean nothing.

11 minutes ago, drjolo said:

When you have ampglow - you should have dark flats

In this image, prove me you cannot replace the darkflat by a constant (right figure) (of course darkflat plot has been y shifted to be visible on the flat plot): 

It is not because you see ampglow it will be a problem. Especially when you scale the darkflat to the flat....

11 minutes ago, drjolo said:

And how much noise is introduced into the final image by dark flat?

We agree it is not really a problem of noise.

21 minutes ago, vlaiv said:

Why leave all that fixed pattern noise in the image?

In the flat????

The bias only applies on flats.

And if you take a look at our plots. That is really not a big deal.

Of course master dark is very importants for lights. Because lights have a very low level in comparison of flats.

10 minutes ago, vlaiv said:

I did not even mention unstable / unusable bias.

My ASI1600 has larger mean bias value than in short exposure. If I used bias - I would end up getting "negative dark current" in my flats.

Not if you use constant....