Calibrating Video Monitors 1

Calibrating Video Monitors

Bob Currier
Synthetic Aperture
www.synthetic-ap.com

When previewing video output, its important that the video monitor
be calibrated. Proper monitor calibration ensures that what you see
today will match what you see tomorrow, and that the judgements
and decisions you make based on what you see remain valid. Echo
Fire provides built-in tools to make the calibration process simpler,
allowing you to calibrate frequently.
Not everyone sees colors and brightness the same. If monitor settings
were left up to personal preference, everyones monitor would be set
differently, making it impossible for people to agree on what video
footage actually looked like and therefore what changes might be
needed. By choosing a calibration standard we dont necessarily make
the picture look its bestthats a subjective judgement in any case
but we attempt to make it look standard. If everyone viewing a project
adheres to the same standard, then there will be much less disagree-
ment over what, if any, changes are needed.

Monitor Differences

Even calibrated video monitors will differ in appearance due to a
number of factors. Different monitors use different phosphors in the
CRT. For NTSC, the standard phosphors are called SMPTE-C. For PAL,
the standard phosphors are called EBU. If possible, choose a monitor
with the appropriate standard phosphors.
Phosphors also wear out over time. In constant use, a video monitor
can be signicantly darker after only two years of use. For critical
applications, it should be replaced. Some broadcast monitors have cal-
ibration probes that actually read the brightness and color values from
the screen and automatically compensate for such phosphor wear.
However, these are expensive and rarely found in most studios.
2 Calibrating Video Monitors

The white point, or color temperature, is another difference between
monitors. The broadcast standard is a white point of 6500K. Most tele-
vision sets, in an effort to produce a brighter picture, use a white point
of 9300K or higher, making the image brighter, but also much bluer. If
your video monitor has selectable white point, choose 6500K. If your
monitor does not, be aware of the color shifts caused by the different
white point.

Why You Want a Real
Video Monitor

One of the rst questions asked by people just starting with video is
Cant I just use my spare television for video monitoring?
The answer is: yes, but you dont want to if you can afford a better
alternative.
Monitoring on a television set is a big step up from trying to do it on a
computer monitor. You get to see color differences (although with
some other distortion) and interlace problems, which are the two
main items that cause problems with computer-generated footage. But
there are distinct advantages to using a real video monitor, despite the
additional cost. And by real video monitor, we mean a monitor pur-
pose-built for monitoring video signals, not for watching TV.
Weve already discussed two of the differences: color temperature and
standard phosphors. Color temperature is the more important of
these and, fortunately, its an option found on most video monitors.
Standard SMPTE-C or EBU phosphors are nice, but do add to the cost
of the monitor.
The big advantage of a real video monitor is that it comes with a Blue
Only button. Pressing this button routes the blue color signal to all
three CRT guns, giving you a black-and-white picture representing
just the blue portion of the image. This serves two purposes: the blue
portion of the image is often the noisiest, so viewing just blue gives
you a better idea of how noisy your material is; but more importantly,
using just the blue channel is an important part of the calibration pro-
cess. There are solutions to the lack of a Blue Only option, but having
it does make calibration much simpler.
Professional video monitors also offer a variety of other options, and
you can spend as much money as you want buying the biggest, most
Calibrating Video Monitors 3

accurate monitor available. But having a monitor with standard phos-
phors, correct white point, and a Blue Only button will make video
monitoring more accurate and simpler for you.

Calibrating the
Monitor

To calibrate your video monitor, display a set of SMPTE color bars. Be
sure that the bars you use are correctly calibrated. Depending on your
video output board, codec, and other factors, the color bars must be
generated differently. Using incorrect color bars will mean that your
monitor will not be calibrated correctly.
Many of the color bar image les youll nd oating around on the
net are not correct. One source of correct color bars is Test Pattern
Maker, a free Macintosh utility program available from <http://
www.synthetic-ap.com>.

Adjusting Chroma and
Hue

To adjust the Chroma and Hue controls, rst locate them on the mon-
itor. They may be located behind a door, and the Hue control may be
labeled Phase on some monitors. Some monitors also have a control
lock function which disables the controls; if your monitor has such a
lock, make sure the controls are unlocked. Next locate and engage the
Blue Only control on your monitor. If your monitor doesnt have a
Blue Only control, you can make the adjustments by viewing the
monitor through a Wratten 47B dark blue photographic lter, which
can be purchased at any well-stocked camera store. Some monitors
have individual controls for the red, green and blue guns instead of a
Blue Only switch; in that case, disable the red and green guns so you
are left with a blue image.
With the Blue Only switch engaged, or while viewing through the 47B
lter, you should see four brighter bars with three darker bars separat-
ing them. At the bottom of each of the four brighter bars is a small
rectangular bar segment. Pay no attention to the other parts of the
display.
You can now start adjusting the Hue and Chroma controls. The goal is
to make the color and brightness of the brighter vertical bars match
the rectangular bar segments below them using only the Hue and
Chroma controls. Adjusting the Hue control mainly affects the two
middle bars, while adjusting the Chroma control mainly affects the
4 Calibrating Video Monitors

two outside bars. Continue adjusting both controls until all four bars
match. Once all bars match, turn off the Blue Only switch.

Adjusting Brightness and
Contrast

Locate the Brightness control on the monitor. Find the sixth (red) bar
on the screen. Directly below this bar at the bottom of the screen you
should see three narrow vertical bars which are different shades of
gray. If the gray bars arent visible, increase the Brightness control
until the three bars can be clearly seen.
Reduce the Brightness control until the middle gray bar just disap-
pears from the screen. The three gray bars are known as the PLUGE
(Picture Line-Up Generating Equipment) bars. The middle bar should
be black, the right bar just barely visible as a very dark gray, and the
leftmost bar should also be black and blend into the middle bar,
Now locate the Contrast control. Adjust it until the white reference
square at the lower left of the screen is bright enough to appear white,
but not so bright that it is too bright to look at or causes the adjacent
squares to glow. The Brightness and Contrast controls interact, so just
keep adjusting them until you get the right combination of settings.
Once you have the Brightness and Contrast controls adjusted, the
monitor calibration is complete.
Depending on your video output card, and the codec its using, the leftmost of
these three bars may be missing and the same shade of gray as the middle bar.
This is a limitation of the codecs ability to produce a blacker-than-black video
level. While not ideal, it wont stop you from being able to calibrate your mon-
itor: simply concentrate on the middle bar as you make the adjustments
described.