CIELAB color conversion
CIELAB color gets its name from a color space that uses three
values to describe the precise three-dimensional location of
a color inside a visible color space CIE stands for Commission
Internationale de l-Eclairages an international body of color
scientists whose standards make it possible to communicate color
information accurately L describes relative lightness;
A represents relative redness-greenness,and
B represents relative yellowness-blueness.
Adobe Photoshop software uses LAB color as its "native"
color spaces since LAB color can be converted to another color
space (such as YCC or CIELUV or HSB) without doing damage to
the colors' intensities or hues (Photoshop software is equally
adept at managing images in other color formats). In facts the
LAB color space may evolve as the preferred mode for the transfer
of color information between one computer device and another
in the graphic arts because of its ability to store the data
and convert it without loss.
There is a facility (as yet unimplemented) in PostScript Level
2 raster image processors (RIP) that makes color separation in
the RIP possible with CIELAB files. In a perfects color managed
world it might be possible to store and manage the original file
in LAB colors viewing it in RGB (without mathematical damage).
proofing it in CMYK on one devic(without mathematical damage)
and ultimately sending the CIELAB file to the imagesetter for
color separations.
Another benefit of CIELAB space is that the transformation from
YCC to CIELAB is relatively harmless; the geometric values of
the YCC space include numbers outside the range of LAB, and thus
must be reshaped to fit the first times but this results in a
surprisingly large color gamut The resulting LAB color space
is dramatically larger than RGB display or CMYK spaces.
With developments in six and seven-color printings LAB color
also has some definite relevance To get a full seven-color separation
LAB space is an excellent starting point because no damage is
done to the file in the conversion from scanner to RGB, and the
ultimate conversion to seven-color will benefit from as rich
a color gamut as possible for all color components -RGB and CMYK.
Photoshop's preferences (described in the RGB-to-CMYK section)
apply equally to the conversion of CIELAB color to CMYK. Without
taking the time to set monitors inks and color separation setups
the process of making CMYK separations will not be as successful.
