As we saw in an earlier blog post, the ISO definition used when you take photographs is based on the brightness of the resulting JPEGs, not on any inherent property of the sensor. Which is something to remember whenever you see anyone talking about manufacturers ‘cheating’ on their ISO figures.

So long as the final JPEG image comes out at the correct brightness (which we'll be testing), manufacturers can do whatever they want with their sensors (and image processing). And, as we saw, if they’re using the Relative Exposure Index definition for pattern light metering, they get to choose what the ‘correct’ brightness is, as well. This provides the scope for manufacturers to do some interesting things to boost dynamic range.

Sensitivity (ISO) in digital imaging seems to be the subject of quite a lot of confusion - it’s becoming common to hear talk of manufacturers 'cheating with ISO.' So we thought it made sense look at why sensitivity appears hard to pin down, why we use the definition we do and how it’s actually not as complicated as it can sometimes seem.