[argyllcms] Re: Feature request (and an implied question)

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 27 Jul 2010 13:49:24 +1000

Ben Goren wrote:
spotread -a -v already shows ambient light levels in lux. Would it be possible
to also show light levels in EV units?

The conversion (for ISO 100) is:

     EV = log2(lux / 2.5)
    lux = 2.5 * 2**EV

As I understand it, EV (Exposure value) represents a camera shutter speed and 
aperture
combination. For a given film speed (ISO), desired exposure (K factor) and 
light level
there will be a resulting suggested EV, but EV itself is not a measure of the 
light level.
So I don't think this belongs in spotread.

It seems pretty trivial to set up a calculation (ie. by hand or with a 
spreadsheet)
that would convert lux to EV given the ISO and the desired exposure. (Of course 
you
also have to take into account whether you are measuring light reflected from 
the
subject, or illumination levels.)

Graeme Gill.

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