Re: Eye-One as Desitometer
Re: Eye-One as Desitometer
- Subject: Re: Eye-One as Desitometer
- From: Phil Green <email@hidden>
- Date: Thu, 06 Sep 2001 15:13:12 +0100
- Organization: LCP
"Vanderlinden, Thomas M." wrote:
>
"...if like other GM spectros it will give you
>
> a density reading"
>
>
>
as far as I can tell, I cannot get density readings directly,
>
only Lab. (plus the every 10 nanometer spectral data)
>
Does anyone know a method for converting
>
Lab readings to density readings?
Yes - although it might not be as simple as you hoped. First you need to
multiply the spectral data by the photopic luminous efficiency
(v-lambda) curve at the 10nm intervals of your data, to give an overall
reflectance weighted by the visual system response - call it R. Then do
D = -log10(R) where D is the density you want and log10 is the base 10
log function.
A densitometer should in principle produce the same result, although the
exact reading may differ due to instrument characteristics such as the
filters used.
ISO 5 series has more details if you want to know how a densitometer
does it.
I'll post the v-lambda data and a spreadsheet with the calculation on
http://www.digitalcolour.org/understanding sometime in the next few
days.
>
"Murray-Davies equation:
>
> A = (1-10^-Dt)/(1-10^-Ds) where A is the dot area, Ds and Dt the density
>
> of the solid and halftone respectively"
>
>
>
"I've been away from such language too long.
>
what does "10^" mean?
10 to the power of... - in other words, the base 10 antilog.
It should work if you type it into Excel just as I wrote it.
--
Phil Green
Colour Imaging Group
School of Printing and Publishing
LCP
Elephant and Castle, London SE1 6SB
Tel: +44 020 7514 6759 Fax: +44 020 7514 6772
http://www.digitalcolour.org