Re: Infering the Lightness Range of a device
Re: Infering the Lightness Range of a device
- Subject: Re: Infering the Lightness Range of a device
- From: "Andre Schützenhofer" <email@hidden>
- Date: Fri, 07 Dec 2001 16:44:05 +0100
That can't be the case in actuality? We all know that the printing
conditions that this profile represent does not have a "black point" equals
to "perfect black" but rather around L* = 18.
I think a normal transformation (perceptual + relcol with BPC on + sat)
always uses the complete dynamic range of L, so the LUTs in a profile are
"clean" - with substrate color calculated out of the measured data and
scaled to L* = 100 (lightning conditions D50) as well as scaled to L* = 0
regarding the black point. The program creates LUTs dependent on the
situation of the gamut's size of L, but in cases of transformation lightness
is relative. After transformation, "black ink" has to be switched on - to
display the correct black of the device. I assume this relates to the
information given by the measurement of the Field CMYK = 100/100/100/100 in
the testform or something like that, in any case a value representing the
blackest black of the device. The B2A1 Tag from absolute colorimetry depends
on the total amount of ink and GCR or UCR settings, graybalance and so on,
defined by the operator who created the profile. So, what we see on monitor
or proof is not the blackest black possible at all but the blackest black
possible regarding this conditions. Therefore, Lightness is a relative
"factor" and there has to be a "black point tag" or anything else which
includes this information. Black point compensation on extends the dynamic
range of lightness in case of relative colorimetrical rendering from
"absolute black" to "perfect black".
Please somebody correct me if I'm wrong with that.
Regards, Andre Schuetzenhofer
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