What ISO means on a CMOS sensor ?

Started Feb 27, 2004 | Discussions thread
kazub Junior Member • Posts: 37
Re: ISO is amplfier gain on sensor. (nt)

Nozkan wrote:

So I just wonder whether it is something IN the sensor or just the
DIGIC circuit ? (I know this may vary on CCD)... Do we set CMOS to
ISO 800, or just command DIGIC to brigthen image 2 times

It is gain control in A/D converter, in neither the sensor nor DIGIC. Each pixel element of the CMOS sensor also has also amplifier, but it is difficult to control the gain of 6 mega amps at the same time.

If we assume the range of voltage from the sensor is from 0.0V to 1.0V, A/D converter converts this analog voltage to 12bit digital data, which is 0 to 4096. This is a definition of base ISO of the sensor.

If we want high ISO, for example ISO 200, A/D converter converts 0.0V to 0.5V analog voltage into 0 to 4096 digital data. The input of 0.5V to 1.0V is neglected as saturated. If ISO 400 (800), then the range is 0.0V to 0.25V (0.125V), etc.

This is the same thing to expand and amplify the low voltage analog input and this means to enhance noise.

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