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Dead pixels?

 
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Harald



Joined: 13 May 2011
Posts: 601
Location: Steinberg, Norway

PostPosted: Wed Mar 25, 2020 11:53 am    Post subject: Dead pixels? Reply with quote

Hi there good people..

I have been using Zerene Stacker for some years now.
Very happy with it. It does a wonderful job with my minerals and insects..

One question:

I get some red and green short stripes, is this dead pixels?
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Harald

Lier Fotoklubb / NSFF
AFIAP / CPS
BGF / GMV
http://www.500px.com/blender11
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 20649
Location: Richland, Washington State, USA

PostPosted: Wed Mar 25, 2020 8:51 pm    Post subject: Reply with quote

Probably these are hot pixels. Hot pixels behave normally for short exposures, but get "bright" for long exposures because they accumulate charge from electrical leakage in addition to light.

There's a new feature in Zerene Stacker that applies here. See https://www.photomacrography.net/forum/viewtopic.php?t=41343 .

--Rik
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Harald



Joined: 13 May 2011
Posts: 601
Location: Steinberg, Norway

PostPosted: Thu Mar 26, 2020 12:36 pm    Post subject: Reply with quote

Yeah,
If you can afford pro version....
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Harald

Lier Fotoklubb / NSFF
AFIAP / CPS
BGF / GMV
http://www.500px.com/blender11
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 20649
Location: Richland, Washington State, USA

PostPosted: Thu Mar 26, 2020 2:20 pm    Post subject: Reply with quote

Otherwise the standard approach is to add light, so as to enable a shorter exposure at same ISO setting. (Shortening the exposure by increasing the ISO setting is not effective, because that approach does not change the ratio of light to leakage.)

If you have other tools that support context aware filling and some sort of batch automation, such as Photoshop and GIMP, then you may be able to use those tools to pre-process your source images by masking the hot pixels and replacing them with nearby content, before stacking the results.

Unfortunately I do not have a recipe available for exactly how to do that.

--Rik

Edited to add: for GIMP, consider using Heal Selection (Resynthesizer) as described at https://patdavid.net/2012/08/getting-around-in-gimp-heal-selection.html .


Last edited by rjlittlefield on Sun Mar 29, 2020 10:07 am; edited 1 time in total
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Harald



Joined: 13 May 2011
Posts: 601
Location: Steinberg, Norway

PostPosted: Thu Mar 26, 2020 2:32 pm    Post subject: Reply with quote

Hi,
What speed do you recommend?

You do a wonderful job on The Zerene Stacker my friend.
I've been using for some years now and I've recommend it to other I know.
A friend og mine working at The Norwegian University with photographing insects. I made him switch from Helicon Very Happy
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Kind Regards
Harald

Lier Fotoklubb / NSFF
AFIAP / CPS
BGF / GMV
http://www.500px.com/blender11
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rjlittlefield
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Joined: 01 Aug 2006
Posts: 20649
Location: Richland, Washington State, USA

PostPosted: Thu Mar 26, 2020 8:51 pm    Post subject: Reply with quote

I cannot make a specific recommendation about speed. Too much depends on the sensor and operating conditions, for example whether Live View is being used which makes the sensor get hot. You will have to run your own tests.

With my Canon T1i camera (yes, I know, an ancient sensor), at 1 second there are maybe 6 annoyingly bright hot pixels, at 5 seconds it grows to more like 35, and at 30 seconds the mask I made has over 150 spots.

BTW, another attack on hot pixels, if you are shooting raw, is to use a raw converter that can be told about defective photosites. dcraw and any of its derivatives come to mine. Again I have no recipe at hand.

Thank you for the kind words about Zerene Stacker. I am hoping that you merely had to illustrate its advantages for your friend, with no coercion required. Rolling Eyes

--Rik
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Bob-O-Rama



Joined: 06 Dec 2014
Posts: 64
Location: Allentown, PA, USA, Earth, etc.

PostPosted: Tue Mar 31, 2020 1:24 pm    Post subject: Look fo hot / dead pixel mapping in camera Reply with quote

Many modern cameras include built in hot pixel / dead pixel mapping. If your's does, you can run it and not worry about it for a month or so. If you already have a series you want to repair, this is surprising easy to do with Image Magick and some light weight scripting. Once you identify the (x,y) of the wonky pixel, you can have ImageMagick replace it with a average from surrounding pixels using their pixel math stuff.

-- Bob
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https://bob-o-rama.smugmug.com/
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