[Aavso-photometry] Re: Cosmic Rays

[Michael Newberry]

About Wolfgang Renz' "maximum deviant" method...

I just asked if we are actually talking about the "Max operator". Upon 
reflection, I realize that it is probably an obscure term to some people. 
And after reading and thinking more about Wolggang's original posting, I 
think that is indeed what we are talking about. Let me be more detailed 
about what I think he is describing:

    Starting with a collection of images, produce an image containing the 
maximum pixel value at each location, relative to the normalized image set. 
The term "normalized" means that all the images are adjusted to a common 
overall brightness. Normalization removes gross offsets between images so 
that the pixel values overlap, revealing the distribution of values around a 
typical value. Very accurate normalization is a requirement of any ranking 
or clipping method, and the Max operation is a member of that club.

If my description is what Wolfgang is proposing, then it is a good 
technique---but not a new one. We've had that as a feature in Mira Pro for 
something like 10 years. For people using that software, it is listed in the 
"Combine Images" dialog as the "Maximum Value" operation, about half way 
down the list of methods. In general, this technique is used for detecting 
transient phenomena. In astronomy it is used for finding moving sources 
(e.g., an asteroid), which produces a characteristic signature that is a 
trail of images of the source.

Does this sound like what Wolfgang is describing?

Michael Newberry

----- Original Message ----- 
From: "Michael Newberry" <mnewberry at mirametrics.com>
To: "Ben Davies" <ben at davies.net>; <aavso-photometry at mira.aavso.org>
Sent: Saturday, January 28, 2006 12:42 PM
Subject: Re: [Aavso-photometry] Re: Cosmic Rays


> What are we talking about here---does anyone know? It sounds to me like 
> just the Max operator. I asked Wolfgang about that yesterday but haven't 
> gotten a response.
>
> Michael
>
> ----- Original Message ----- 
> From: "Ben Davies" <ben at davies.net>
> To: <aavso-photometry at mira.aavso.org>
> Sent: Saturday, January 28, 2006 12:15 PM
> Subject: [Aavso-photometry] Re: Cosmic Rays
>
>
>> Justin,
>>
>> Great idea.  You da man!
>>
>> But Wolfgang must be consulted on details.  This is his idea, and he is 
>> very clear on what is needed..
>>
>> What language are you planning on?  I have a Fortran compiler laying 
>> about, but nothing in C.
>>
>> Ben
>>
>>
>>
>>
>> Justin Pryzby wrote:
>>
>>>Hey Ben,
>>>
>>>If it would be useful, I could implement a command-line implementation
>>>of "higest absolute deviant" combinbination this weekend.  Something
>>>like
>>>  ./combine-deviants --output most-deviants.fits *.fits
>>>
>>>
>>
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>>
>>
>
>
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