ohho - 1 year ago 73

C Question

How to convert from an exposure value to lux? Thanks!

i.e. what's the formula behind this chart?

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Answer Source

Forget the math on Wikipedia. By inspecting the table to which you linked, it's possible to see a pattern:

EV Lux -1 1.25 -0.5 1.75 0 2.50 0.5 3.50 1 5.00 1.5 7.00 2 10.00 2.5 14.00 3 20.00 3.5 28.00 4 40.00 ...

1 EV is 5 Lux. 2 EV is 10 Lux. 3 EV is 20 Lux. So, it looks logarithmic:

```
lux = (2 ^ ev) * 2.5;
```

(2 to the power of EV, times 2.5)

C-like:

```
#include <math.h>
double evToLux(double ev) {
return pow(2, ev) * 2.5;
}
```

**Update**

Wikipedia has this formula:

**Update 2**

It is important to point out that EV is dependent on the film speed (ISO). All above is true only for ISO 100. It is easy to convert to other speeds, though:

`EV(at ISO 100) == EV(at ISO 200) - 1`

(H/T Nikolai Ruhe)

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