"Black sun" effect in CMOS sensors

  • Thread starter Thread starter AlexVM
  • Start date Start date
  • Tags Tags
    Cmos Sensors Sun
Click For Summary

Discussion Overview

The discussion centers around the "Black sun" effect observed in CMOS cameras, where very bright spots in images appear as dark areas. Participants explore potential reasons for this phenomenon, including technical explanations related to sensor behavior and comparisons to other imaging technologies.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants propose that heating of the semiconductor sensor may lead to faster discharge of the image, resulting in zero charge and thus a black appearance.
  • Another viewpoint suggests that a concept from analogue television, where noise pulses create dark spots, might be applicable to digital sensors.
  • A participant notes that the ability to remove the effect via software indicates that the software identifies bright areas and compensates accordingly.
  • One participant mentions not having experienced the effect in their own CMOS cameras and requests examples with specific image details.
  • Another participant shares a link to a document that discusses the phenomenon, although they express difficulty accessing it due to file size.
  • A later reply cites a specific excerpt from the document, explaining that excessive light can cause a pixel's potential well to spill over, leading to negative values in the sensor's output and resulting in black spots.
  • One participant acknowledges familiarity with blooming in CCD sensors but states they have not encountered the black spot effect.

Areas of Agreement / Disagreement

Participants express varying levels of familiarity with the "Black sun" effect, and while some propose technical explanations, others indicate they have not observed the phenomenon themselves. Multiple competing views and hypotheses remain without consensus.

Contextual Notes

There are limitations regarding the assumptions made about sensor behavior, the definitions of terms like "blooming," and the specific conditions under which the "Black sun" effect occurs. The discussion does not resolve these aspects.

AlexVM
Messages
5
Reaction score
0
Hi,
I would like to understand the reason for the "Black sun" effect that occurs in CMOS cameras (very bright spots appear as dark).

Thanks,
ALex
 
Engineering news on Phys.org
I do not know, but here are a couple of possibilities.

If the semiconductor sensor is heated it may become conductive and discharge the image faster than it can be integrated, giving zero charge = black.

In analogue television systems, a noise pulse exceeding white was gated to produce a dark spot on the screen. Dark noise is less distracting than bright noise. Maybe the same concept is being applied to digital sensors.

The fact that it can be removed by software suggests the software looks for the bright area and paints white in the hole.
 
AlexVM said:
Hi,
I would like to understand the reason for the "Black sun" effect that occurs in CMOS cameras (very bright spots appear as dark).

Thanks,
ALex

I haven't seen this effect on any of my cameras with CMOS sensors4 or 5 cameras ... do you have any image examples
that also show image details ... shutter speed, f-stop ?
 
T.Leedy said:
You might check ... <link>
It might be interesting, but I cannot download a 26MByte file over my slow link. Can someone please review it and post an extract of the relevant paragraph?
 
So sorry, I didn't notice the size of the file. It says (verbatim):
"If too much light impinges on the pixel of some CMOS image sensors, here as well the potential pot can spill over (called blooming for CCDs) and cause an increase of the reference level. This in turn causes due to the subtraction of signal and reference negative values appearing as „black spots“ in the bright areas."

I think what the author meant to say was:
"If too much light impinges on a given pixel in some CMOS image sensors, the potential well of that pixel can spill over and increase the reference level (this is called 'blooming' for CCD sensors). This in turn, causes an error in the sensor's output due to the subtraction of signal and reference. Since the subtraction results in a negative value, the output of the sensor is set to zero. Thus the 'black spots' appear in a field of bright pixels."
I hope I didn't butcher the author's meaning too much.
 
Last edited:
interesting ... yes, am well familiar with blooming on CCD sensors
just have never see the black spot effect

Dave
 

Similar threads

What Is the Fundamental Unit of CCD/CMOS Sensors Called?
  • · Replies 25 ·
Replies
25
Views
3K
Sensor "pixels" count vs digital image output pixels count
  • · Replies 8 ·
Replies
8
Views
2K
CMOS Sensor with external reset control
  • · Replies 7 ·
Replies
7
Views
2K
Underwater piezoelectric sensor array receive sensitivity
  • · Replies 16 ·
Replies
16
Views
1K
How Do Image Sensors Convert Light into Electrical Signals?
  • · Replies 2 ·
Replies
2
Views
2K
Should New Hardware Designs Specify CMOS or TTL Compatibility from the Start?
  • · Replies 4 ·
Replies
4
Views
2K
Cmos imaging sensor response
  • · Replies 3 ·
Replies
3
Views
4K
Linear image sensor CCD or CMOS
  • · Replies 1 ·
Replies
1
Views
5K
Eddy current position sensor circuit
  • · Replies 5 ·
Replies
5
Views
3K
Graduate Characterizing Electron Beam w/ CMOS-Camera or Faraday Cup
  • · Replies 19 ·
Replies
19
Views
4K