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Initial disclaimer, my hardware in question is a PTZ video surveillance camera (Hikvision DS-2DE5425IW-AE) which would make it off topic for Photography StackExchange.

However the issue I'm having is a general one, that is related to any image sensor. So my desire to post here was because I thought there might be a chance there is someone who encountered a similar issue in some other digital camera (still or video). If however the veterans here consider this off topic regardless, I do apologize deeply and kindly ask for a suggestion of another StackExchange site where it might be appropriate to ask this.

My situation: I just got a new (claimed as unused/unopened) camera and during night time when the camera automatic exposure settings uses high gain (iso) values there is a big ghost-like purple stain/figure visible over half of the image...

That same stain however is totally not visible during day time (image looks clear and normal) or even during night time when zoomed in at some bright, well lit area... Also manually reducing the gain value (to about half) hides it, but is beside the point since it reduces night visibility (which I need) significantly.

The shape of the figure stays the same even when zooming in, so to me that would seem to confirm the stain is not on the lens elements (and upon inspection, visually they seem fine and clear). It seems the "stain" or whatever it is, is on the image sensor itself...

What I'm wondering is what is it and what could have caused this. I've searched the internet for water damaged sensors or laser damaged sensors.. and nothing looks like this... So I'm really interested in a theory what is causing(or has caused) this specific type of defect, and if it is potentially fixable.

Here is a snapshot demonstrating the issue: purple stain purple stain marked

And a video:

YouTube demo - Stain visible during PTZ operation

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    \$\begingroup\$ Is there a dome over that camera? If so, it could be a reflection off of some indicator light or similar. \$\endgroup\$
    – dgatwood
    Commented Jul 30, 2018 at 5:11
  • \$\begingroup\$ Would reflection on a dome over the camera stay the same with zooming, as seen in the YouTube video? \$\endgroup\$
    – xiota
    Commented Jul 30, 2018 at 6:26
  • \$\begingroup\$ @dgatwood, no dome, but I did think initially that it could be the IR illuminator light bleeding through some holes on the sensor. However I made sure they(IR LEDs) were completely off and also in the video I made a test by switching the IR night mode on purpose, the stain unfortunately remained visible, which indicates that is not it either... \$\endgroup\$
    – Ivan Kovacevic
    Commented Jul 30, 2018 at 9:42

1 Answer 1

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The defect may be an example of Fixed-Pattern Noise, which worsen with high ISO, prolonged use, and increased temperatures. FPN is usually associated with long exposures, although there are different types that may occur in different situations.

  • DSNU (dark signal non-uniformity) is the offset from the average across the imaging array at a particular setting (temperature, integration time) but not external illumination

  • PRNU (photo response non-uniformity), which describes the gain or ratio between optical power on a pixel versus the electrical signal output.

You may be able to avoid the problem by using lower ISO settings or noise reduction techniques that specifically target FPN.

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