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How often do you see dead pixels?


Saul Oliveira
 

Hello, hope everyone is ok,

I was wondering how often nowadays do you guys find dead or stuck pixels in modern cameras (Red´s, Alexa´s, Venice...) and how do you deal with them?

Best regards and good health to everyone.
Saul Oliveira
First AC
Spain


Rob van Gelder
 

Not often, but the latest repair ( not sensor related) at Arri for one of our Alexa Mini’s showed one dead pixel, which apparently they are able to hide.


Rob van Gelder
Big Eye Co.ltd.
Bangkok - Thailand
Head of maintenance / international contacts




On 14 Apr BE 2563, at 15:42, Saul Oliveira <oliveira_saul@...> wrote:

Hello, hope everyone is ok,

I was wondering how often nowadays do you guys find dead or stuck pixels in modern cameras (Red´s, Alexa´s, Venice...) and how do you deal with them?


Keith Putnam
 

Until very recently I'd be tempted to say "not often", but it's possible there are a lot more of them out there than we think.

Following a heads-up from VFX, I was looking at R G B channel separations from ProRes 444 footage that we'd been shooting with some fairly old Alexas on my show, and as it turned out both of our main camera bodies had "dead" or "stuck" photosites in the green and red channels which weren't visible in full RGB.

So if you're curious about the camera you're using, shoot few seconds of a fairly neutral subject like a gray wall or a gray card or similar, take the footage into Resolve and separate the channels so you can compare them individually. You may find some hot spots you won't otherwise see.

Keith Putnam
Local 600 DIT
New York City


Olaf Matthes
 

I'd say it all depends on what we mean with "see" when we talk about
dead pixels. Most cameras keep track of dead pixels internaly and either
"repair" those pixel sites in camera or place a "mark" (some reserved
value that would not normally occur when reading the sensor) in the RAW
data so that the debayering software downstream can deal with it.

For example in Phantom Cine cameras for most data formats the camera
marks the dead pixels and it is the job of the debayer to first "fix"
them by doing some interpolation of surrounding unclipped pixels (of the
same color). But in order for the camera to know about the position of
dead pixels you need to perform a sensor calibration.
So any new dead pixels that have appeared after the last calibration
will not get fixed in software.

I've seen dead pixel fixing code in Arri software as well, so I assume
that also Arri cameras mark dead pixels that are known at time of shooting.

I'll not mention any numbers or manufacturers, but you'de be surprised
of how many pixel sites in a sensor can actually be dead in a totally
usable camera! It is just that the software makes sure you never get to
see them.

A lot of my work is for stop-motion animation where people shoot with
DSLRs thouthands of individual frames. Since the cameras have live-view
switched on all the time (i.e. for the whole shooting day, which might
only produce a few seconds of final output) there is the additional
problem that some dead pixels only show up (i.e. stop to behave
normally) once a certain sensor temperature is reached. In those cases
it is quite common to do an extra run of image based dead-pixel
detection which has the side effect of sometimes detecting very fine
bright detail as dead pixels.


Olaf Matthes
EU-based freelance software developer


Art Adams
 

Not often, but the latest repair ( not sensor related) at Arri for one of our Alexa Mini’s showed one dead pixel, which apparently they are able to hide.

 

This is standard procedure in most cameras. Some automate the process internally and ask you to do it quite often. In our case, you’d capture a raw file and use ARRI Raw Converter to create a mask that hides it. The process isn’t completely automatic and requires a little more work on your part, but we feel it’s more accurate. You shouldn’t have to do it very often at all.

 

Here’s a video on how it’s done:

 

https://www.youtube.com/watch?v=7ZHLPPgxdZw&feature=youtu.be

 

Or we’ll take care of it if you send the camera in for service.

_______________________________________________________
Art 
Adams
Cinema Lens Specialist
ARRI Inc.
3700 Vanowen Street
BurbankCA 91505
www.arri.com 

 
aadams@...

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