[argyllcms] Re: Black&White Profiling Printing
- From: David Cary <cdecary@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Sat, 17 Dec 2011 15:33:33 +1300
Thank you. That gives me something to chew on!
Regards
David
On Sat, Dec 17, 2011 at 3:10 PM, Graeme Gill <graeme@xxxxxxxxxxxxx> wrote:
> David Cary wrote:
>> Also I would like to ask which value to use from a chart read to
>> manually make your own digital negative QTR profile. I am using the L
>> value from Lab, but chartread can read a wedge automatically for me.
>> The output is XYZ and I am unclear if I should use the Y value (and if
>> a gamma is already applied to this value) or if I should average the
>> X, Y and Z values (and if a gamma is already applied to these values
>> for the Yule-Nielsen effect)
>
> Hi,
> you can use chartread -l or -L to get D50 L* values. Y (and L*
> which is derived from it) uses the photopic luminous efficiency
> function, which is essentially the monochrome appearance, so no,
> you don't average X, Y and Z values. Note that in printing it is
> usual to normalize the XYZ readings to the white point of the medium
> using a chromatic adaptation matrix. Since these are measurements
> rather than a printing model, Yule-Nielsen doesn't come into it.
> (Typically if you were fitting a printing model that depends on
> dot overlaps, dot gain etc., you would work in linear light Y values
> rather than L*. If you are creating a purely mathematical curve model
> then either might be used.)
>
>
> Graeme Gill.
>
Other related posts:
