Graphics Programs Reference
In-Depth Information
Measuring black is difficult and few products provide the level of accuracy to nail the black
target. Calibrating to an accurate black, day in, day out, requires a sensor capable of reading
very low levels as well as a display that has very fine adjustment granularity. My Sony Artisan
is able to calibrate to
+
/
-
.02 cd/m
2
or 10X more accurately than previously described. That
means any of the images in this test file will be displayed exactly the same. Day in and day
out, the same image previews identically.
Visual Calibration
There are a number of tools that allow a user to “calibrate” and profile a
display using software and a pair of eyeballs. I put calibrate in quotes
because I don't think much of visual display calibration and profiling.
This is certainly better than plopping a display out of a box and onto your
desk and ignoring any calibration whatsoever. Using visual calibration is
a small step in the right direction. Our display should produce a consis-
tent color preview over its lifetime. Visual calibration is just fraught prob-
lems. The human visual system provides a wonderful pair of instruments
for comparing colors. However, our eyes are very poor at providing a ref-
erence. In order to achieve absolute reference, an instrument is required.
Instruments do not experience the psychophysical effects, for example,
of drinking fine red wine. Some may recall that Adobe had a utility called
Adobe Gamma
that was used to visually calibrate and profile a display. The
Macintosh has a built-in visual calibration and profile utility that works
in a similar fashion.
There are a number of instruments and software packages that will
accomplish the task of calibration and profiling. The price point for an
instrument-based package is so low that I simply can't believe anyone
serious enough about color management to read this topic would resort
to using a software-only calibration and profile tool. Consider the cost of
a set of ink cartridges for your printer. You will save many times the cost
of such an instrument in the reduction of wasted inks and paper.
Sidebar
Calibration for LCDs and CRTs:
The calibration of a display is somewhat unique compared
to other devices for several reasons. Every display requires a unique process for calibration due
to the enormous differences between displays. CRTs are different than LCDs, and each offer
many different types of controls.
Ideally all calibration is achieved by physically altering the display electronics. Integrated
systems (display, colorimeter, and software) can achieve this result best. Sophisticated displays
with advanced controls combined with top-of-the-line calibration software also can achieve this
type of physical calibration through user interaction.
The opposite end of the spectrum is LUT-based calibration. All adjustments are made in the
graphic card. The graphic LUT is 8 bits. As we have seen, 8-bit data through an 8-bit LUT results
