[john0213]

nice correction dcstep!!

I would also side the fact that ISO is the sensitivity of the sensor. the mechanism of the sensor in theory can somewhat be easily explained.

Sensor is composed of many tiny cells. each square of cell resolves a certain amount of pixel. when light hits the sensor, the sensor is electrically charged before it detects any light. the higher the sensitivity, the higher the voltage is being chrarged onto the sensor. therefore, when boosting the ISO, one is essentially boosting the voltage to increase the sensitivity of the sensor chip.

As we all know, there is noise in electricity. the higher the voltage, the higher the noise. hence, when stronger charge gets put through to the sensor chip, it also records the noise in the electricity too, and that's how the noise is introduced in the image.