Re: Targeting for different illuminants
Re: Targeting for different illuminants
- Subject: Re: Targeting for different illuminants
- From: Steve Upton <email@hidden>
- Date: Mon, 2 Apr 2001 09:42:36 -0700
At 4:14 PM -0600 4/1/01, Dan Reid wrote:
Hey color geeks,
Heya Dan
Any body given some thought to targeting images for specific illuminants?
Yup...
Most of our profiles are built using a D50 illuminant L*a*b* space. When we
convert from one profile to the next the profiles usually contain a D50
L*a*b* PCS.
Or a D50 XYZ space, we really don't have a choice with this one as it
is hard coded in the spec in the CMM's
I am thinking that we would need to use a L*a*b* space with the
targeted illuminant (i.e. Illuminant A [incandescent], L*a*b* space) and
then use this as either an abstract profile or simulation profile in three
fold transform.
You can hack the flavor of Lab by using an abstract profile but as
David Tobie mentioned you really should do it from the Spectral data.
If you are using the Spectrolino, download their tool ColorLab from
www.logosoft.de. It will allow you to read targets with spectral data
for each patch rather than D50 Lab. You can then convert the spectral
values to many different flavors of Lab including D50, D55, D65, D70,
A, C, ideal) you can also convert them to various flavors of density
if you want. (whether or not D55, D70 are recognized standards or
just convenient notations is a different issue)
I know we have a D65 L*a*b* profile but not sure if another
illuminant could be used instead? Any thoughts on this topic?
Again, I think you can hack the Lab flavor but you should really
start with the spectral data if you can.
We use this technique in our custom profiling solutions for clients.
Tweaking the Lab flavor when profiling can complicate the issue but
when profiling ink/papers that exhibit metamerism it can sometimes be
the only way to go to get neutral looking good under specific
lighting conditions. It is important, however to know the lighting
conditions you are shooting for so sometimes we make onsite visits to
determine the environment first.
Regards,
Steve Upton
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