"Black sun" effect in CMOS sensors

In summary, the "black sun" effect occurs when too much light impinges on a pixel in a CMOS sensor, causing an increase in the reference level. This in turn causes dark spots to appear in bright areas of the image.
  • #1
AlexVM
5
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
 
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  • #2
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.
 
  • #3
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 ?
 
  • #5
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?
 
  • #6
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:
  • #7
interesting ... yes, am well familiar with blooming on CCD sensors
just have never see the black spot effect

Dave
 

Related to "Black sun" effect in CMOS sensors

What is the "Black sun" effect in CMOS sensors?

The "Black sun" effect refers to the phenomenon in CMOS sensors where bright light sources, such as the sun or other intense light sources, can cause pixels to become temporarily saturated and appear as a dark spot on the final image.

How does the "Black sun" effect occur in CMOS sensors?

The "Black sun" effect occurs when the intensity of the light source exceeds the dynamic range of the CMOS sensor, causing the pixels in that area to become oversaturated. This results in a dark spot in the final image, even though the light source may be very bright.

What are the consequences of the "Black sun" effect in CMOS sensors?

The "Black sun" effect can cause a loss of detail and contrast in the affected area of the image. It can also result in blooming, where the bright spot spreads into surrounding pixels, further degrading the image quality.

How can the "Black sun" effect be prevented in CMOS sensors?

The "Black sun" effect can be prevented by using a neutral density filter or reducing the exposure time to avoid oversaturating the pixels. Some CMOS sensors also have built-in features to mitigate the effect, such as electronic shutters and anti-blooming circuits.

Can the "Black sun" effect be removed from images taken with CMOS sensors?

While it is not possible to completely remove the "Black sun" effect from images, it can be reduced through post-processing techniques such as HDR imaging or using specialized software to correct the affected areas. However, this may result in a loss of image quality and is not always successful.

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