Re: [MaxImDL] Re: Recommendations for Dithering


Jun 13, 2009

 


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#37109 Jun 13, 2009

I want to start using dithering to get rid of some of the noise in my images.

I assume that, typically, a bright star should move just enough from one group of pixels to another for Maxim to distinguish the move. The number of pixels to select would be a function of the pixel scale (2.176 arcsec per pixel in my case).

The manual gives no guidelines.

Looking at a typical image, a bright star fills about 10 pixels and thus the move should be in the region of 15 pixels in a 40008x2672 image. Does this make sense? Any recommendations?



Dale



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#37127 Jun 14, 2009

The only 'problem' with large dithers is that you have to ensure that your mount settles back to an acceptable guiding error before starting the next exposure.



I typically dither 2 pixels; this is enough for my combination of mount, camera, scope, etc. I also normally use a 20 second delay between exposures



Your milage may vary....



Greg



--- In MaxImDL@yahoogroups.com, "Lawrence D. Lopez" lopez@...> wrote:

>

> Dale:

>

> Large dithered amounts are fine.

>

> Combining dithered images make a bad column or a dead pixel disappear.

> Media, sigma clip, SD Mask or Median work better than average in this

> respect.

>

> Noise is suppressed about the same amount as non dithered, I would expect.

>

> Larry

>

>

> dale.liebenberg wrote:

> > I want to start using dithering to get rid of some of the noise in my images.

> > I assume that, typically, a bright star should move just enough from one group of pixels to another for Maxim to distinguish the move. The number of pixels to select would be a function of the pixel scale (2.176 arcsec per pixel in my case).

> > The manual gives no guidelines.

> > Looking at a typical image, a bright star fills about 10 pixels and thus the move should be in the region of 15 pixels in a 40008x2672 image. Does this make sense? Any recommendations?

> >

> > Dale

> >

> >

> >

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

> >

> > Yahoo! Groups Links

> >

> >

> >

> >

> >

>



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#37128 Jun 14, 2009

Greg:



Are you saying that you have to wait longer for large dithers to settle

down ?

I could certainly see reasons it could matter.

It's an interesting question depending on. as you say mount, camers,

scope, etc.



I haven't done any large dithers.



Larry



greg_in_woodlands wrote: > The only 'problem' with large dithers is that you have to ensure that your mount settles back to an acceptable guiding error before starting the next exposure.

>

> I typically dither 2 pixels; this is enough for my combination of mount, camera, scope, etc. I also normally use a 20 second delay between exposures

>

> Your milage may vary....

>

> Greg

>

>

> --- In MaxImDL@yahoogroups.com, "Lawrence D. Lopez" lopez@...> wrote:

>

>> Dale:

>>

>> Large dithered amounts are fine.

>>

>> Combining dithered images make a bad column or a dead pixel disappear.

>> Media, sigma clip, SD Mask or Median work better than average in this

>> respect.

>>

>> Noise is suppressed about the same amount as non dithered, I would expect.

>>

>> Larry

>>

>>

>> dale.liebenberg wrote:

>>

>>> I want to start using dithering to get rid of some of the noise in my images.

>>> a The number of pixels to select would be a function of the pixel scale (2.176 arcsec per pixel in my case).

>>> The manual gives no guidelines.

>>> Looking at a typical image, a bright star fills about 10 pixels and thus the move should be in the region of 15 pixels in a 40008x2672 image. Does this make sense? Any recommendations?

>>>

>>> Dale

>>>

>>>

>>>

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

>>>

>>> Yahoo! Groups Links

>>>

>>>

>>>

>>>

>>>

>>>

>

>

>

>

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

>

> Yahoo! Groups Links

>

>

>

>

>



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