Matrox Electronic Systems MXO2 - Manual (Page 27)

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Matrox MXO2 Family for PC Product Guide
HDMI Monitor Calibration – Frequently Asked Questions
Q - Why do I need to calibrate my monitor?
A - The color of light in a room affects your perception. Think of a white sheet
of paper. If the light in the room is blue, the sheet of paper will look blue. But
if the light is red, the paper will look red. In the same way, the colors you see
on your monitor will depend on the color of the lighting in the room. The level
of lighting in the room also plays a role.
Manufacturers of televisions, broadcast monitors, and computer monitors
make assumptions about the lighting in your room when adjusting their
factory default settings. Computer monitors are factory adjusted to be used
in brightly lit rooms such as offices. Broadcast monitors are designed for the
lighting typically found in living rooms. Manufacturers of broadcast monitors
take extra care to make sure their red, green, and blue are as close as
possible to those specified by ITU-R Recommendation BT.709 (also known
as Rec 709). Television manufacturers, on the other hand, are more interested
in having their televisions stand out from the crowd in the showroom than in
having exact colors or shades of grey. More often than not, when comparing
the colors on a broadcast monitor to the default setting on a digital television,
you’ll find that the television is too bright and the colors are too saturated.
In addition, variations in manufacturing processes result in variations of the
actual shades of red, green, and blue from monitor to monitor.
Q - Why do HDMI monitors and televisions require more adjustments
than broadcast monitors?
A - Broadcast HD-SDI monitors are manufactured to match the Rec 709
specification. The only adjustments that need to be done on them are those
required to adapt their picture to the environment in which that are used. For
example, in a bright room your eyes will have a harder time perceiving the
2% black pluge bar than in a very dark room. You can adjust the monitor by
increasing the black level (brightness) until you can see the 2% black pluge
bar. Similarly, other controls on the broadcast monitor are there to adapt the
picture on the monitor to its environment, not to compensate for errors in the
manufacturing of the monitor.
In the case of analog component signals, some compensation for
transmission errors might be required even on a broadcast monitor. But for
the discussion here, transmission errors are not an issue because HDMI
monitors and televisions are digital.
Because computer monitor default settings are not designed to display
video in a living room, more parameters need to be adjusted to match
the Rec 709 specification. One would think that television default settings
would closely match those of a broadcast monitor. However, because
television manufacturers set up their television to stand out from the crowd
in the showroom, they also require more adjustments to match the Rec 709
specification.
Q - Why is it so important that my monitor follows the Rec 709 spec?
A - In order to ensure that the picture a video camera is filming is going
to match the picture the viewer is ultimately going to see, the camera
and monitor need to digitize and display colors in exactly the same way.
Otherwise for example, the viewer might see a dark green apple when in
reality the apple was light green. That is why there is a specification, ITU-R
Recommendation BT.709 (also known as Rec 709), that defines how a HD
monitor should display color. It specifies, among other things, a gamma
response of 2.22, the white point, and the exact primaries to be used.
Q - What is the white point?
A - There are several parameters in the Rec 709 spec that define how a
monitor should display colors. One of them is the actual color the monitor
should display when displaying white. It sounds odd, but white can actually
take on slightly different hues. If we take a white piece of paper and look at
it in sunlight at noon and in sunlight at sunset, our eyes perceive a slightly
different hue of white. The one at sunset will be more orange, but our brain
will still see both as white. Rec 709 specifies the exact hue white should
have. It’s roughly what the white sheet of paper looks like under sunlight on
an overcast day at midday. This white is neutral, neither blue nor yellow.
appendix
HDMi Monitor calibration – Frequently asked Questions