Re: Processing AMP glow out of the picture


Dec 6, 2006

 


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

#26897 Dec 6, 2006

Hello,



I wanted to inquire if there is a way to process the AMP glow from the

DSI Pro out of a picture, it shows up in the dark frames I take, but

it seems to still not subtract it from the finnal image.



I use Envisage to capture and MaximDL to process.



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

#26899 Dec 6, 2006

Hello:



How are you combining your darks? And more importantly, how are

you dark-calibrating your images? If you are not subtracting bias

frames from your dark frames then you cannot do anything that "scales"

the dark frames, such as compensating for exposure time differences or

optimally matching darks. I found I had no problem at all getting rid

of the DSI amp glow by taking an average of 10 darks whose exposure

times were the same as all of my images; that is, I use a single

exposure time all night (typically 100 seconds), then take a set of 10

100-second darks and subtract their average from my images. No bias

subtraction is necessary in that case and subtracting the average

(bias not subtracted) dark from my images is also then bias-correcting

them (the images). One other thing to be aware of is bias drift -

even if you do bias subtract your dark frames so that they can be

scaled and such, you need a bias frame taken at the same temperature

as the darks; the mean bias level changes significalntly with

temperature in the DSI cameras. I'm guessing you are already

temperature matching your dark frames as well; even a couple of

degrees C is enough to make a big difference in dark subtraction.



Mike Potter

Baltimore, MD



--- In MaxImDL@yahoogroups.com, "hilmi.kindy" hilmi.kindy@...> wrote:

>

> Hello,

>

> I wanted to inquire if there is a way to process the AMP glow from

the

> DSI Pro out of a picture, it shows up in the dark frames I take, but

> it seems to still not subtract it from the finnal image.

>

> I use Envisage to capture and MaximDL to process.

>



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

#26900 Dec 6, 2006

Hi,



I dont fully understand all what you are saying since I am relatively

new to the imaging scene. Basicaly, I take my dark frames in Envisage

after the camera has settled to ambient temprature, each color takes

me roughly 10 to 15 minutes, so I just use the same darks for all

images.



--- In MaxImDL@yahoogroups.com, "Mike Potter" mike@...> wrote:

>

> Hello:

>

> How are you combining your darks? And more importantly, how

are

> you dark-calibrating your images? If you are not subtracting bias

> frames from your dark frames then you cannot do anything

that "scales"

> the dark frames, such as compensating for exposure time differences

or

> optimally matching darks. I found I had no problem at all getting

rid

> of the DSI amp glow by taking an average of 10 darks whose exposure

> times were the same as all of my images; that is, I use a single

> exposure time all night (typically 100 seconds), then take a set of

10

> 100-second darks and subtract their average from my images. No

bias

> subtraction is necessary in that case and subtracting the average

> (bias not subtracted) dark from my images is also then bias-

correcting

> them (the images). One other thing to be aware of is bias drift -

> even if you do bias subtract your dark frames so that they can be

> scaled and such, you need a bias frame taken at the same

temperature

> as the darks; the mean bias level changes significalntly with

> temperature in the DSI cameras. I'm guessing you are already

> temperature matching your dark frames as well; even a couple of

> degrees C is enough to make a big difference in dark subtraction.

>

> Mike Potter

> Baltimore, MD

>

>

> --- In MaxImDL@yahoogroups.com, "hilmi.kindy" hilmi.kindy@> wrote:

> >

> > Hello,

> >

> > I wanted to inquire if there is a way to process the AMP glow

from

> the

> > DSI Pro out of a picture, it shows up in the dark frames I take,

but

> > it seems to still not subtract it from the finnal image.

> >

> > I use Envisage to capture and MaximDL to process.

> >

>



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

#26906 Dec 7, 2006

Hello again:



I really don't know much about how Envisage works; I've used it

for the few times I wanted to take short exposures as MaxIm doesn't

work well with the DSI cameras for exposures shorter than a second

or so. Check out the "Guide to Astronomical Imaging" in the MaxIm

help files - it'll give you a good introduction to the image

calibration process. I also strongly recommend "The Handbook of

Astronomical Image Processing" - a great book that includes the

software package AIP4WIN, available from Willman-Bell Publishing.

The book contains a lot more than you might need to get started, but

it's a valueable reference you'll go back to many times as your

skill level improves and you discover new questions.



Using the same set of darks for all colors is fine - just make

sure the exposure time and temperature for the darks matches the

exposure time and temperature for your images and it should work.



Mike Potter

Baltimore, MD



--- In MaxImDL@yahoogroups.com, "hilmi.kindy" hilmi.kindy@...>

wrote: >

> Hi,

>

> I dont fully understand all what you are saying since I am

relatively > new to the imaging scene. Basicaly, I take my dark frames in

Envisage > after the camera has settled to ambient temprature, each color

takes > me roughly 10 to 15 minutes, so I just use the same darks for all

> images.

>

>

> --- In MaxImDL@yahoogroups.com, "Mike Potter" mike@> wrote:

> >

> > Hello:

> >

> > How are you combining your darks? And more importantly,

how > are

> > you dark-calibrating your images? If you are not subtracting

bias > > frames from your dark frames then you cannot do anything

> that "scales"

> > the dark frames, such as compensating for exposure time

differences > or

> > optimally matching darks. I found I had no problem at all

getting > rid

> > of the DSI amp glow by taking an average of 10 darks whose

exposure > > times were the same as all of my images; that is, I use a single

> > exposure time all night (typically 100 seconds), then take a set

of > 10

> > 100-second darks and subtract their average from my images. No

> bias

> > subtraction is necessary in that case and subtracting the

average > > (bias not subtracted) dark from my images is also then bias-

> correcting

> > them (the images). One other thing to be aware of is bias

drift - > > even if you do bias subtract your dark frames so that they can

be > > scaled and such, you need a bias frame taken at the same

> temperature

> > as the darks; the mean bias level changes significalntly with

> > temperature in the DSI cameras. I'm guessing you are already

> > temperature matching your dark frames as well; even a couple of

> > degrees C is enough to make a big difference in dark subtraction.

> >

> > Mike Potter

> > Baltimore, MD

> >

> >

> > --- In MaxImDL@yahoogroups.com, "hilmi.kindy" hilmi.kindy@>

wrote: > > >

> > > Hello,

> > >

> > > I wanted to inquire if there is a way to process the AMP glow

> from

> > the

> > > DSI Pro out of a picture, it shows up in the dark frames I

take, > but

> > > it seems to still not subtract it from the finnal image.

> > >

> > > I use Envisage to capture and MaximDL to process.

> > >

> >

>







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