Why expose ETTR and how to do it?

Started 4 months ago | Discussions thread
Erik Kaffehr
OP Erik Kaffehr Veteran Member • Posts: 5,199
Re: Why expose ETTR and how to do it?

Dirk Dittert wrote:

Erik,

thanks for sharing!

I wonder if it would be possible to design an image sensor that can stop the exposure when a certain number of photosite reaches 100% capture capacity. Basically that would be a sensor with protection against clipping.

I don't really think so. Stopping exposure is almost the same as clipping. What really happens is that the photodiode does not really saturate, but the voltage exceeds the maximum of the ADC.

The reason that we don't have global shutters in digital cameras is due to not being able to stop photon detection.
With interline CCDs, global shutter was possible as half the sensor area was used to save electron charges. With CMOS, it would also be possible to add a buffer area for charges, but that means reducing full well capacity.

The task sensor designers have is managing sensor estate. Adding more features reduces the area of the sensor collecting electron charges.

Keep also in mind that camera sensors are basically analogue devices and photosites are probably the most complex analogue devices made.
Modern CMOS technology allows the sensor to output digital signals, but most of the sensor is still an analogue device.

Best regards

Erik

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Erik Kaffehr
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