Re: Lab Values in measure file??
Re: Lab Values in measure file??
- Subject: Re: Lab Values in measure file??
- From: <email@hidden>
- Date: Tue, 20 Feb 2007 10:39:52 -0500
Jon,
What does the data in the nm380 through nm730 columns
mean in a measurement file?
This is spectral data.
The "nm" is the abbreviation for nanometer, a measure of
the wavelenght of light (=0.000000001 meter). 380 nm
corresponds to blue/UV while 730 nm is the infrared, with
all visible wavelenghts in between.
For example, for a color patch measured in reflection, the
value labeled nm530 (a green hue) is the amount of light
reflected between 525 and 535 nm, i.e. a 10 nm range. The
reflectance is usually normalized between 0 and 1 or
between 0 and 100%.
The spectral data is used to compute XYZ data, by
multiplying the reflectance at each wavelenght by a set of
three reference sensitivity curves of the human eye,
corresponding roughly to red, green and blue, which are
collectively called the Standard Observer.
There are two Standard Observers, the 2 degree
Observer(devised by the CIE in 1931) corresponding to
patches subtending a small 2 degree angular field relative
to the eye (most suited for graphic applications), and the
10 degree Observer (devised by the CIE in 1964),
corresponding to patches covering a 10 degree angular
field (better suited for paint and textile applications).
XYZ is then converted to L*a*b* values.
The advantages of using spectral data over L*a*b* are:
1- you can re-compute L*a*b* for another Illuminant (or
Observer) with minimal error
2- spectral data is required to get density values
3- spectral data is required to analyse the perceived
color differences of one patch(color inconstancy) or
between two patches (metamerism) under different lights.
Various softwares will open and translate spectral data
into colorimetric values such as L*a*b*. I suggest you try
the free trial version of PatchTool:
http://www.babelcolor.com/main_level/download.htm
which will let you open many types of spectral and
colorimetric files, and see the corresponding colors.
Danny Pascale
email@hidden
www.BabelColor.com
On Tue, 20 Feb 2007 07:38:42 -0600
Jon Crook <email@hidden> wrote:
What does the data in the nm380 through nm730 columns
mean in a measurement
file? Can this info be translated into Lab values for
each patch? If not,
how can I obtain the Lab values for each patch from the
text document?
--
Jonathan Crook
Prepress Technician
Corporate Image
www.corp-image.com
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