[junousia]

Hi


I have one very technical question on image sensors. If I know image sensor's sensitivity in mV/Lux-sec e.g. 900 mV/Lux-sec, is it possible to convert it to ISO speed or estimate the ISO speed?

[clackers]

Well, if that's max sensitivity, that's ISO 100, J.

Everything else is just a multiple of its readings.

[Winder]

Hi


I have one very technical question on image sensors. If I know image sensor's sensitivity in mV/Lux-sec e.g. 900 mV/Lux-sec, is it possible to convert it to ISO speed or estimate the ISO speed?

You can get close, but it varies by camera.

The ISO 12232:2006 standard not really about sensitivity like it was in the film days. Digital is about the application of digital amplification to achieve correct exposure. The ISO 12232:2006 standard created the The Recommended Exposure Index (REI), allows the manufacturer to specify a camera model’s EI choices arbitrarily. This means that ISO 100 might not be the same on a Fuji X-T1 as it is on a Pentax K-3. 18% gray is the film standard which Fuji is still using, but most manufacturers are metering for 12-13% gray.

Your digital camera meter is exposing for a RGB value of 119,119,119 or a scene brightness of 46.x%. The sensor only has 1 sensitivity, so the image processor has to apply digital gain to the image to boost brightness. The ability to apply digital gain without boosting noise is why two different companies can use the same sensor and get different results. Better image processors produce cleaner images.

[wombat2go]

The sensor only has 1 sensitivity, so the image processor has to apply digital gain to the image to boost brightness. The ability to apply digital gain without boosting noise is why two different companies can use the same sensor and get different results. Better image processors produce cleaner images.

I think that these days, the "image sensor" module incorporates the hardware analog gain stages and the adc units
The gains (iso settings) are needed before the adc.

For example, Onsemi describe the above in their detailed publications of data for their image sensors.
( These are scientific/industrial sensors, but I think quite similar to the consumer dslr ones)
http://www.onsemi.com/pub_link/Collateral/NOIV1SN025KA-D.PDF
This example is for a 35mm 5T cmos mono/Bayer module with global/rolling shutter.
Figure 5 page 9 shows a block diagram including the adjustable gains of the column multiplexer and the adc front end amplifiers.
The "iso" settings for these are uploaded to registers in the module.

[junousia]

I think that these days, the "image sensor" module incorporates the hardware analog gain stages and the adc units
The gains (iso settings) are needed before the adc.

For example, Onsemi describe the above in their detailed publications of data for their image sensors.
( These are scientific/industrial sensors, but I think quite similar to the consumer dslr ones)
http://www.onsemi.com/pub_link/Collateral/NOIV1SN025KA-D.PDF
This example is for a 35mm 5T cmos mono/Bayer module with global/rolling shutter.
Figure 5 page 9 shows a block diagram including the adjustable gains of the column multiplexer and the adc front end amplifiers.
The "iso" settings for these are uploaded to registers in the module.

Thanks Winder and wombat2go.

[wombat2go]

It is "de nada" and I think your query is relevant

But I see that ISO 12232 has some problems:
Cost US$123+ for a copy.
It was an attempt to carry film photographer's iso ratings into digital camera settings, a different technology with different bench-marks.
The low light noise of silicon image sensors has declined over 10 years while film does not have an equivalent base or ongoing improvement.
The standard did not stipulate a "base " Signal -to-Noise ratio.

The above means that camera providers can set the base iso freely, so iso above the base are free too, and different from camera to camara.

Am I on the right track here?

[junousia]

I'm not sure, but native (or base) ISO speed is usually is the sensitivity where the sensor gives its best performance, as determined by dynamic range (large) and noise (minimal). All depend on image sensor and also on image prosessor. Native ISO can be then e.g. ISO 100 or ISO 200.