# LR3 auto removal of hot/stuck pixels



## rjalex (Dec 7, 2010)

The other night for the first time I shot pics in the dark with my new 5Dmk2 and upon browsing them in Loup(E) mode I saw a little white spot in the middle of the sky. A plane light ?  Nope it appeared in all other shots even in different sky regions. 

As soon I zoomed the image to 100% though the spot automagically DISAPPEARED and appears to be gone forever.

How does LR perform this trick ? Does it interpolate the adjacent pixels ?

How does it determine it's a stuck pixel and not a little star or a little light ?

Thank you very much.
Bob


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## Victoria Bampton (Dec 7, 2010)

Magic... 

Ok, I don't know.  I don't remember ever seeing it published anywhere, but it's been in ACR for years too.


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## Mark Sirota (Dec 7, 2010)

I don't know the answer, but I can take a guess...

Stuck pixels aren't exactly pixels -- they are photosites.  In the Bayer array, it will be just one of the red, green, or blue photosites.  I'm guessing that in the demosaic phase, if it notices one photosite at "maximum" value with its neighbors at considerably less than maximum, it'll assume that one's stuck.

The problem with that theory is that it should have taken care of it in the standard preview, not just in the 1:1.  I had previously believed that either one was developed from the same demosaiced data in the Camera Raw cache, and so if the detection happens in the demosaic then I think it should have been reflected in the standard preview.  So my explanation is probably incomplete.


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## rjalex (Dec 7, 2010)

If anyone is curious I can send one of the affected CR2s and let you play with it !  What I see is what translates to one single WHITE pixel on the LCD and when zoomed 100% looked for a moment made of more than one "photodiode" but then when I rvert to the non 100% view it's gone forever


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## clee01l (Dec 8, 2010)

Mark Sirota said:


> I don't know the answer, but I can take a guess...
> 
> Stuck pixels aren't exactly pixels -- they are photosites.  In the Bayer array, it will be just one of the red, green, or blue photosites.  I'm guessing that in the demosaic phase, if it notices one photosite at "maximum" value with its neighbors at considerably less than maximum, it'll assume that one's stuck.
> 
> The problem with that theory is that it should have taken care of it in the standard preview, not just in the 1:1.  I had previously believed that either one was developed from the same demosaiced data in the Camera Raw cache, and so if the detection happens in the demosaic then I think it should have been reflected in the standard preview.  So my explanation is probably incomplete.


What I think happens is that LR uses the embedded JPEG thumbnail for the standard preview until you need to render 1:1. At that point it reads the data from the file and processes the hot pixels away.  The embedded JPEG  from the camera file still contains the hot pixel.  Some cameras like my Pentax automatically heal the hot pixels in the SOOC processing so I never see the pixel at any resolution.


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