Re: [MaxImDL] Re: Questions about flat fields and dark frames with Maxim DL software


Jan 16, 2010

 


----------------------------

#39556 Jan 16, 2010

Hello,



This is my first post to the user-group. I am expecting delivery of brand new APO refractor. Then afterwards I will purchase ccd camera for imaging. I am still in the learning process of astrophotography, and would appreciate help and advice from members of this group. My concern has to do with flat fields and dark frames. MaximDL can be used to apply a dark frame and a flat field to individual light frames, correct? Yet many astrophotographers maintain a library of dark frames and flat fields, so what I want to know is why do you need to have "master darks" and "master flats"? Another question I have involves the following: Flat fields can be taken at different temps than the dark frames; however you must take separate dark frames for you flats at the same exposure time and temp as your flats. Can members of this group help me understand this further? I apologize if this topic has been brought up many times in the past, but it's important I understand the application of dark frames and flat fields so I can be successful with my imaging goals. Any advice/comments/suggestions is greatly appreciated and very helpful.



Best regards,



Fernando



----------------------------

#39557 Jan 16, 2010

Hi Fernando,



Try reading the Maxim online help - it talks through a lot of the basics.



Here's a good place to start:



www.cyanogen.com/help/maximdl/Calibration.htm



Regards,



John





2010/1/16 fernandorivera3 fernandorivera3@...>

>

>

> Hello,

>

> This is my first post to the user-group. I am expecting delivery of brand

> new APO refractor. Then afterwards I will purchase ccd camera for imaging. I

> am still in the learning process of astrophotography, and would appreciate

> help and advice from members of this group. My concern has to do with flat

> fields and dark frames. MaximDL can be used to apply a dark frame and a flat

> field to individual light frames, correct? Yet many astrophotographers

> maintain a library of dark frames and flat fields, so what I want to know is

> why do you need to have "master darks" and "master flats"? Another question

> I have involves the following: Flat fields can be taken at different temps

> than the dark frames; however you must take separate dark frames for you

> flats at the same exposure time and temp as your flats. Can members of this

> group help me understand this further? I apologize if this topic has been

> brought up many times in the past, but it's important I understand the

> application of dark frames and flat fields so I can be successful with my

> imaging goals. Any advice/comments/suggestions is greatly appreciated and

> very helpful.

>

> Best regards,

>

> Fernando

>

>

>





[Non-text portions of this message have been removed]



----------------------------

#39558 Jan 17, 2010

below...





"May You Go Among The Imperishable Stars"

Joe Mize www.cav-sfo.com

Chiefland Astronomy Village, Fla.

----- Original Message -----

From: "fernandorivera3" fernandorivera3@...>

To: MaxImDL@yahoogroups.com>

Sent: Saturday, January 16, 2010 9:48 PM

Subject: [MaxImDL] Questions about flat fields and dark frames with Maxim DL

software





> Hello,

>

> This is my first post to the user-group. I am expecting delivery of brand

> new APO refractor. Then afterwards I will purchase ccd camera for imaging.

> I am still in the learning process of astrophotography, and would

> appreciate help and advice from members of this group. My concern has to

> do with flat fields and dark frames. MaximDL can be used to apply a dark

> frame and a flat field to individual light frames, correct? Yet many

> astrophotographers maintain a library of dark frames and flat fields, so

> what I want to know is why do you need to have "master darks" and "master

> flats"?



..."Masters Calibration" files are the 'combination's of all your Flat and

Dark 'sub-frames', one Master is made for each set type. Each Master is

then used to perform the actual Calibration of your Light sub-frames before

they are Aligned and Stacked. Maxim does this quite transparently when you

choose Process > Calibrate or Calibrate-All on individual or groups of Light

frames. Maxim reads each Master's FITS Header choosing the required Masters

matching the Light frame to perform the Calibration of the Light Frame/s.



Another question I have involves the following: Flat fields can be taken at

different temps than the dark frames; however you must take separate dark

frames for you flats at the same exposure time and temp as your flats.



..."Flat Darks" are only required if your Flats have extremely long exposure

times, upwards of 1min each. However for short exposure Flats, 3-10sec,

making zero time Bias frames and Masters will remove the read noise in Flats

just as well as Flat Darks. Bias frames are much easier and quicker to make

than Flat Darks.



Can members of this group help me understand this further? I apologize if

this topic has been brought up many times in the past, but it's important I

understand the application of dark frames and flat fields so I can be

successful with my imaging goals. Any advice/comments/suggestions is greatly

appreciated and very helpful.



...The reason some people maintain Calibration 'Libraries', Bias, Flat and

Dark sub-frames, is new sub-frames can be added when needed for future

Master Calibration files while the older Masters are being used. Yes, you

can Delete your Bias, Dark and Flat sub-frames 'after' you've made your

Masters to save disk space. HTH...joe :)



> Best regards,

>

> Fernando

>

>

>

---------------

>

> Yahoo! Groups Links

>

>

>

>







----------------------------

#39559 Jan 17, 2010

The purpose of dark frames is to remove "glow" from a few sorts of issues in the electronics of the CCD camera. However, whenever you subtract anything you increase the noise in your image. This is why people make a "library dark", which is an average of a large number of dark frames acquired at the desired temperature. By averaging a large number of them together, you reduce (but don't eliminate) the noise but keep the dark "signal".



An alternative is to get a camera with such small (and uniform!) dark glow that it is better NOT to subtract a dark frame. This is the approach I followed. I have had good results without darks for a number of years now (for me, light pollution is the issue, not dark current).



On Jan 16, 2010, at 9:48 PM, fernandorivera3 wrote:



> Hello,

>

> This is my first post to the user-group. I am expecting delivery of brand new APO refractor. Then afterwards I will purchase ccd camera for imaging. I am still in the learning process of astrophotography, and would appreciate help and advice from members of this group. My concern has to do with flat fields and dark frames. MaximDL can be used to apply a dark frame and a flat field to individual light frames, correct? Yet many astrophotographers maintain a library of dark frames and flat fields, so what I want to know is why do you need to have "master darks" and "master flats"? Another question I have involves the following: Flat fields can be taken at different temps than the dark frames; however you must take separate dark frames for you flats at the same exposure time and temp as your flats. Can members of this group help me understand this further? I apologize if this topic has been brought up many times in the past, but it's important I understand the application of dar!

> k frames and flat fields so I can be successful with my imaging goals. Any advice/comments/suggestions is greatly appreciated and very helpful.

>

> Best regards,

>

> Fernando



Robert J. Vanderbei

Princeton University

www.princeton.edu/~rvdb

"When I have nothing to say, my lips are sealed. Say it once, why say it again?" -- Talking Heads









[Non-text portions of this message have been removed]



----------------------------

#39560 Jan 17, 2010

" An alternative is to get a camera with such small (and uniform!) dark glow

that it is better NOT to subtract a dark frame. This is the approach I

followed. I have had good results without darks for a number of years now

(for me, light pollution is the issue, not dark current)."



I'd like to know which camera type or brand has, as you state, an almost

inexistent dark glow! I'll surely buy one if it's right priced!



Antonio Zanardo



----- Original Message -----

From: "Robert Vanderbei" rvdb@...>

To: MaxImDL@yahoogroups.com>

Sent: Sunday, January 17, 2010 5:56 PM

Subject: Re: [MaxImDL] Questions about flat fields and dark frames with

Maxim DL software





> The purpose of dark frames is to remove "glow" from a few sorts of issues

> in the electronics of the CCD camera. However, whenever you subtract

> anything you increase the noise in your image. This is why people make a

> "library dark", which is an average of a large number of dark frames

> acquired at the desired temperature. By averaging a large number of them

> together, you reduce (but don't eliminate) the noise but keep the dark

> "signal".

>

> An alternative is to get a camera with such small (and uniform!) dark glow

> that it is better NOT to subtract a dark frame. This is the approach I

> followed. I have had good results without darks for a number of years now

> (for me, light pollution is the issue, not dark current).

>

>

> On Jan 16, 2010, at 9:48 PM, fernandorivera3 wrote:

>

>> Hello,

>>

>> This is my first post to the user-group. I am expecting delivery of brand

>> new APO refractor. Then afterwards I will purchase ccd camera for

>> imaging. I am still in the learning process of astrophotography, and

>> would appreciate help and advice from members of this group. My concern

>> has to do with flat fields and dark frames. MaximDL can be used to apply

>> a dark frame and a flat field to individual light frames, correct? Yet

>> many astrophotographers maintain a library of dark frames and flat

>> fields, so what I want to know is why do you need to have "master darks"

>> and "master flats"? Another question I have involves the following: Flat

>> fields can be taken at different temps than the dark frames; however you

>> must take separate dark frames for you flats at the same exposure time

>> and temp as your flats. Can members of this group help me understand this

>> further? I apologize if this topic has been brought up many times in the

>> past, but it's important I understand the application of dar!

>> k frames and flat fields so I can be successful with my imaging goals.

>> Any advice/comments/suggestions is greatly appreciated and very helpful.

>>

>> Best regards,

>>

>> Fernando

>

> Robert J. Vanderbei

> Princeton University

> www.princeton.edu/~rvdb

> "When I have nothing to say, my lips are sealed. Say it once, why say it

> again?" -- Talking Heads

>

>

>

>

> [Non-text portions of this message have been removed]

>

>

>

---------------

>

> Yahoo! Groups Links

>

>

>







----------------------------

#39561 Jan 17, 2010

Although adequate cooling and read noise subtraction can reduce the noise of dark currents to low levels, I'm not aware of any means as effective as dark subtraction at noise reduction. Even cameras with detectors that are not cost constrained , such as the HST images, use dark subtraction.



Regards,

GaryB

--- In MaxImDL@yahoogroups.com, "antonio zanardo" antoniozanardo@...> wrote:

>

> " An alternative is to get a camera with such small (and uniform!) dark glow

> that it is better NOT to subtract a dark frame. This is the approach I

> followed. I have had good results without darks for a number of years now

> (for me, light pollution is the issue, not dark current)."

>

> I'd like to know which camera type or brand has, as you state, an almost

> inexistent dark glow! I'll surely buy one if it's right priced!

>

> Antonio Zanardo

>

>

> ----- Original Message -----

> From: "Robert Vanderbei" rvdb@...>

> To: MaxImDL@yahoogroups.com>

> Sent: Sunday, January 17, 2010 5:56 PM

> Subject: Re: [MaxImDL] Questions about flat fields and dark frames with

> Maxim DL software

>

>

> > The purpose of dark frames is to remove "glow" from a few sorts of issues

> > in the electronics of the CCD camera. However, whenever you subtract

> > anything you increase the noise in your image. This is why people make a

> > "library dark", which is an average of a large number of dark frames

> > acquired at the desired temperature. By averaging a large number of them

> > together, you reduce (but don't eliminate) the noise but keep the dark

> > "signal".

> >

> > An alternative is to get a camera with such small (and uniform!) dark glow

> > that it is better NOT to subtract a dark frame. This is the approach I

> > followed. I have had good results without darks for a number of years now

> > (for me, light pollution is the issue, not dark current).

> >

> >

> > On Jan 16, 2010, at 9:48 PM, fernandorivera3 wrote:

> >

> >> Hello,

> >>

> >> This is my first post to the user-group. I am expecting delivery of brand

> >> new APO refractor. Then afterwards I will purchase ccd camera for

> >> imaging. I am still in the learning process of astrophotography, and

> >> would appreciate help and advice from members of this group. My concern

> >> has to do with flat fields and dark frames. MaximDL can be used to apply

> >> a dark frame and a flat field to individual light frames, correct? Yet

> >> many astrophotographers maintain a library of dark frames and flat

> >> fields, so what I want to know is why do you need to have "master darks"

> >> and "master flats"? Another question I have involves the following: Flat

> >> fields can be taken at different temps than the dark frames; however you

> >> must take separate dark frames for you flats at the same exposure time

> >> and temp as your flats. Can members of this group help me understand this

> >> further? I apologize if this topic has been brought up many times in the

> >> past, but it's important I understand the application of dar!

> >> k frames and flat fields so I can be successful with my imaging goals.

> >> Any advice/comments/suggestions is greatly appreciated and very helpful.

> >>

> >> Best regards,

> >>

> >> Fernando

> >

> > Robert J. Vanderbei

> > Princeton University

> > www.princeton.edu/~rvdb

> > "When I have nothing to say, my lips are sealed. Say it once, why say it

> > again?" -- Talking Heads

> >

> >

> >

> >

> > [Non-text portions of this message have been removed]

> >

> >

> >

---------------

> >

> > Yahoo! Groups Links

> >

> >

> >

>



----------------------------

#39562 Jan 17, 2010

But to be clear, you don't use dark subtraction to remove noise. Dark

subtraction always adds noise. You use it to remove a non-uniform bias

produced by each pixel's individual dark current contribution to the signal.

The noise component of the original image is always left behind, and a

certain amount of noise from the dark frame itself is added.



Chris



*****************************************

Chris L Peterson

Cloudbait Observatory

www.cloudbait.com



----- Original Message -----

From: "Gary B" gburk@...>

To: MaxImDL@yahoogroups.com>

Sent: Sunday, January 17, 2010 10:24 AM

Subject: [MaxImDL] Re: Questions about flat fields and dark frames with

Maxim DL software





> Although adequate cooling and read noise subtraction can reduce the noise

> of dark currents to low levels, I'm not aware of any means as effective as

> dark subtraction at noise reduction. Even cameras with detectors that are

> not cost constrained , such as the HST images, use dark subtraction.



----------------------------

#39563 Jan 17, 2010

Agreed Chris, "noise" is the unpredictable component, whereas the fixed-pattern component can be considered a non-uniform bias (or offset).



However. as compared to not doing a dark-subtraction at all, calling it a "noise reduction" is not far in error. This is because the dark current at each photosite is an unknown that is added to the valid signal component. In general any component of a signal that is not the result of the intended phenomenon is "noise".



Just hair-splitting!

--- In MaxImDL@yahoogroups.com, "Chris Peterson" cpeterson@...> wrote:

>

> But to be clear, you don't use dark subtraction to remove noise. Dark

> subtraction always adds noise. You use it to remove a non-uniform bias

> produced by each pixel's individual dark current contribution to the signal.

> The noise component of the original image is always left behind, and a

> certain amount of noise from the dark frame itself is added.

>

> Chris

>

> *****************************************

> Chris L Peterson

> Cloudbait Observatory

> www.cloudbait.com

>

>

> ----- Original Message -----

> From: "Gary B" gburk@...>

> To: MaxImDL@yahoogroups.com>

> Sent: Sunday, January 17, 2010 10:24 AM

> Subject: [MaxImDL] Re: Questions about flat fields and dark frames with

> Maxim DL software

>

>

> > Although adequate cooling and read noise subtraction can reduce the noise

> > of dark currents to low levels, I'm not aware of any means as effective as

> > dark subtraction at noise reduction. Even cameras with detectors that are

> > not cost constrained , such as the HST images, use dark subtraction.

>







----------------------------

#39564 Jan 17, 2010

Cameras based well-cooled Sony chips generally have very low and highly uniform dark current. A few camera makers now offer cameras with these Sony chips. I use a Starlight Express SXV-H9. Two caveats: I don't think Sony (or anyone else) has come out with large-format, monochrome, antiblooming chips. The CCD in my camera is "only" 1.4 megapixels. It is monochrome and antiblooming, though.

On Jan 17, 2010, at 12:11 PM, antonio zanardo wrote:



> " An alternative is to get a camera with such small (and uniform!) dark glow

> that it is better NOT to subtract a dark frame. This is the approach I

> followed. I have had good results without darks for a number of years now

> (for me, light pollution is the issue, not dark current)."

>

> I'd like to know which camera type or brand has, as you state, an almost

> inexistent dark glow! I'll surely buy one if it's right priced!

>

> Antonio Zanardo



Robert J. Vanderbei

Princeton University

www.princeton.edu/~rvdb

"Conserve energy? How could I not?" -- Entropy Man











[Non-text portions of this message have been removed]



----------------------------

#39565 Jan 17, 2010

Chris beat me to it in pointing out that dark subtraction does not reduce noise. Rather, it eliminates an unwanted signal.



I'd be happy to provide raw dark frames and light frames to anyone who would like to demonstrate that dark-subtraction produces better results with my camera. :-)



--Bob

On Jan 17, 2010, at 12:24 PM, Gary B wrote:



> Although adequate cooling and read noise subtraction can reduce the noise of dark currents to low levels, I'm not aware of any means as effective as dark subtraction at noise reduction. Even cameras with detectors that are not cost constrained , such as the HST images, use dark subtraction.

>

> Regards,

> GaryB



Robert J. Vanderbei

Princeton University

www.princeton.edu/~rvdb

"Exaggeration is a billion times worse than understatement"









[Non-text portions of this message have been removed]



----------------------------

#39566 Jan 17, 2010

Hi there,







I'm looking at importing my DSLR reference darks gathered previously from

temperatures 30 deg -90deg F. I understand I will need to add FITS header

information into the files so MaximDL can find them during automated

processing. Does someone have a step by step they can link to for me?







Also, however, its interesting, does those in the know think I need even to

use darks this time of year (35 deg F)?







Thanks,







Paul







[Non-text portions of this message have been removed]



----------------------------

#39586 Jan 18, 2010

Fernando,



I'm just one step ahead of you.... For a non temp regulated DSLR, I use for example a master dark (1 per 5 degrees F temperature (..35 deg, 40 deg, 45 deg...etc.) AFTER I get my 50 or so frames (at the same outside temperature) from the camera, combine them and re-save the result as...'masterdark.fit'. Then, no need to keep all those LARGE files around, then, so I erase them and then use the master when processing the 'lights' taken from the telescope.



Paul --- In MaxImDL@yahoogroups.com, "fernandorivera3" fernandorivera3@...> wrote:

>

> Hello,

>

> This is my first post to the user-group. I am expecting delivery of brand new APO refractor. Then afterwards I will purchase ccd camera for imaging. I am still in the learning process of astrophotography, and would appreciate help and advice from members of this group. My concern has to do with flat fields and dark frames. MaximDL can be used to apply a dark frame and a flat field to individual light frames, correct? Yet many astrophotographers maintain a library of dark frames and flat fields, so what I want to know is why do you need to have "master darks" and "master flats"? Another question I have involves the following: Flat fields can be taken at different temps than the dark frames; however you must take separate dark frames for you flats at the same exposure time and temp as your flats. Can members of this group help me understand this further? I apologize if this topic has been brought up many times in the past, but it's important I understand the application of dark frames and flat fields so I can be successful with my imaging goals. Any advice/comments/suggestions is greatly appreciated and very helpful.

>

> Best regards,

>

> Fernando

>



----------------------------

#39615 Jan 19, 2010

I wonder if the semantics of "noise" could be substituted for the word "uncertainty." The result of uncertainty being the "grainy" uncertain values which people interpret as a physical manifestation of "noise" in images.

Just a thought.



So your paragraph below would read as:



"But to be clear, you don't use dark subtraction to remove uncertainty. Dark subtraction always increases the uncertainty of values.... The uncertainty of the original image is always left behind and this is increased a bit by subtracting a dark from.... "



Do you think that would help?



Adam



*-----Original Message-----

*From: Chris Peterson [mailto:cpeterson@...]

*Sent: Sunday, January 17, 2010 10:49 AM

*To: MaxImDL@yahoogroups.com

*Subject: Re: [MaxImDL] Re: Questions about flat fields and dark frames with Maxim DL software

*

*But to be clear, you don't use dark subtraction to remove noise. Dark

*subtraction always adds noise. You use it to remove a non-uniform bias

*produced by each pixel's individual dark current contribution to the signal.

*The noise component of the original image is always left behind, and a

*certain amount of noise from the dark frame itself is added.

*

*Chris

*

******************************************

*Chris L Peterson

*Cloudbait Observatory

*www.cloudbait.com

*

*

*----- Original Message -----

*From: "Gary B" gburk@...>

*To: MaxImDL@yahoogroups.com>

*Sent: Sunday, January 17, 2010 10:24 AM

*Subject: [MaxImDL] Re: Questions about flat fields and dark frames with

*Maxim DL software

*

*

*> Although adequate cooling and read noise subtraction can reduce the noise

*> of dark currents to low levels, I'm not aware of any means as effective as

*> dark subtraction at noise reduction. Even cameras with detectors that are

*> not cost constrained , such as the HST images, use dark subtraction.

*

*







----------------------------

#39616 Jan 19, 2010

It's certainly accurate to use "uncertainty" for "noise" in this way. How

much it helps, I don't know. The term "noise" is pretty deeply embedded in

signal processing theory. Given a choice, I'd rather keep its meaning as it

is- uncertainty- and come up with a new term for all the fixed pattern

artifacts, and unwanted signal artifacts that plague imagers- the stuff that

is usually called noise even though it isn't noise in the usual signal

processing sense.



At the least, it can only help to qualify "noise" when it's used, so that we

all know what kind of artifacts are under discussion.



Chris



*****************************************

Chris L Peterson

Cloudbait Observatory

www.cloudbait.com



----- Original Message -----

From: "Adam Block" ngc1535@...>

To: MaxImDL@yahoogroups.com>

Sent: Tuesday, January 19, 2010 3:02 PM

Subject: Re: [MaxImDL] Re: Questions about flat fields and dark frames with

Maxim DL software





>I wonder if the semantics of "noise" could be substituted for the word

>"uncertainty." The result of uncertainty being the "grainy" uncertain

>values which people interpret as a physical manifestation of "noise" in

>images.

> Just a thought.

>

> So your paragraph below would read as:

>

> "But to be clear, you don't use dark subtraction to remove uncertainty.

> Dark subtraction always increases the uncertainty of values.... The

> uncertainty of the original image is always left behind and this is

> increased a bit by subtracting a dark from.... "

>

> Do you think that would help?

>

> Adam



----------------------------

#39619 Jan 19, 2010

Adam Block wrote: > I wonder if the semantics of "noise" could be substituted for the word "uncertainty."



No, because in the domain of statistics those are essentially identical concepts.



Dark current can be thought of as a fixed pattern, which needs to be removed

from the image.



More precisely, dark current is a stochastic process, which has a different rate

of accumulation in each pixel. It's a random phenomenon, yes, but it has a

well-defined average rate. You can remove the average, but not the randomness.



What you see in EACH PIXEL when you capture an image is an average amount of

dark current, plus dark current noise. The dark current noise is equal to the

square root of the number of electrons detected.



So if a particular pixel produces an average of 256 electrons of dark current in

a one minute exposure (at a certain temperature), then there will also be 16

electrons of noise in every exposure.



But an individual exposure produces a single number. You need to capture a

bunch of images and do some statistics. If you take 20 exposures, and look at

the same pixel in each, you can calculate an average and standard deviation*.

Our example pixel will typically produce an average of 256, and a standard

deviation of 16. In reality each time you perform this experiment you'll get a

slightly different answer... that's statistics for you.



Now, if you *don't* subtract a dark frame, from a certain point of view the

extra "damage" to the image is "noise". But it is not strictly speaking noise

from a statistical viewpoint. It would more accurately be called "systematic

error".



If you understand the physical phenomenon involved, which is to say you

understand the mathematics, then the semantics are totally irrelevant.



Doug



* If you're going to do this experiment, remember that you need to subtract bias

and take into account Photons per ADU.



--



Doug George

dgeorge@...



Diffraction Limited

Makers of Cyanogen Imaging Products

www.cyanogen.com/



100 Craig Henry Dr., Suite 202

Ottawa, Ontario,

Canada, K2G 5W3



Phone: (613) 225-2732

Fax: (613) 225-9688



----------------------------

#39624 Jan 19, 2010

I agree.

I think the issue is that for imagers "noise" and "grainy-images" is so connected with one another there is often an issue of communicating the idea of uncertainty instead of strictly a morphological attribute of images.



Adam



*-----Original Message-----

*From: Chris Peterson [mailto:cpeterson@...]

*Sent: Tuesday, January 19, 2010 03:24 PM

*To: MaxImDL@yahoogroups.com

*Subject: Re: [MaxImDL] Re: Questions about flat fields and dark frames with Maxim DL software

*

*It's certainly accurate to use "uncertainty" for "noise" in this way. How

*much it helps, I don't know. The term "noise" is pretty deeply embedded in

*signal processing theory. Given a choice, I'd rather keep its meaning as it

*is- uncertainty- and come up with a new term for all the fixed pattern

*artifacts, and unwanted signal artifacts that plague imagers- the stuff that

*is usually called noise even though it isn't noise in the usual signal

*processing sense.

*

*At the least, it can only help to qualify "noise" when it's used, so that we

*all know what kind of artifacts are under discussion.

*

*Chris

*

******************************************

*Chris L Peterson

*Cloudbait Observatory

*www.cloudbait.com

*

*

*----- Original Message -----

*From: "Adam Block" ngc1535@...>

*To: MaxImDL@yahoogroups.com>

*Sent: Tuesday, January 19, 2010 3:02 PM

*Subject: Re: [MaxImDL] Re: Questions about flat fields and dark frames with

*Maxim DL software

*

*

*>I wonder if the semantics of "noise" could be substituted for the word

*>"uncertainty." The result of uncertainty being the "grainy" uncertain

*>values which people interpret as a physical manifestation of "noise" in

*>images.

*> Just a thought.

*>

*> So your paragraph below would read as:

*>

*> "But to be clear, you don't use dark subtraction to remove uncertainty.

*> Dark subtraction always increases the uncertainty of values.... The

*> uncertainty of the original image is always left behind and this is

*> increased a bit by subtracting a dark from.... "

*>

*> Do you think that would help?

*>

*> Adam

*

*







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