Color Accuracy -- Problems and Solutions
Since the inception of the PC in 1981 we have demanded more and more color. First color was used
to make games more interesting, and then to make programs easier to use. Color is now exploding
into most of your documents and presentations taking them to the next level of professionalism. We
started out with 4 colors and moved to 8 then 16 colors. We graduated to capabilities as high as 256
colors; and now we have rocketed into the stratosphere with 16 bit (65,000) and 24 bit (16.7 million)
color. And all for what? More accurate and realistic representation of the world around us, or the
world we would like around us. We have now raised expectations for color reproduction on a PC to
the point where we as consumers are driving technology again. If you have ever tried to scan, create
or print anything in color off a PC, you know the horrors that can creep up. Washed out images,
colors askew if not actually wrong, and of course accuracy of gradients are just a few of the problems.
We would like to first address some of the limitations and constraints of the color technologies
currently available on the PC platform due to the technologies, and hardware, and then some
solutions. For some, this will be too technical for others, not technical enough. The intent is to
introduce new ideas to solve some of the problems that may be encountered.
Keep in mind that this is going to be an arduous task. Some of the factors involved are ambient room
lighting, wall and ceiling color and reflectivity, video card, monitor, printer, software and scanner.
This is all without mentioning the Red Green Blue to Cyan Yellow Magenta blacK conversion
problems. Then we have gamma correction, white balance, color temperature and phosphor
chromaticity to take into consideration. Even considering this, we have to be aware of the gamma of
the monitor, video card, scanner, printer and the image itself. With this many variables, one can see
that the likelihood of getting screen images that match printed output perfectly is slim if not
impossible. This would be a good time to explain several terms that are going to be used in this
article, and that you will see along your adventure in color calibration.
GAMMA
The light output from phosphor is not linear to the video driving voltage. It is proportional to the
video driving voltage raised to the power of "gamma". This means that brighter color is expanded and
darker color is crushed. In monitors and TVs gamma correction circuitry is included to minimize the
effect, thereby giving a truer representation of the video driving voltage input to the CRT. The
gamma figure given here is a corrected gamma function. Uncorrected gamma in phosphor tubes is
usually 2.2. The closer the gamma is to 1 the "truer" the display.
Formula: L=V^(gamma) ; light output = video driving voltage raised to the gamma.
Gamma is typically written as just one number. For instance, for the NEC monitors, the gamma
standard rating is: 2.46.
