On Jan 20, 2010, at 12:38 AM, Jason Cerovac wrote:
On Tue, January 19, 2010 17:42, Stuart F. Biggar wrote:
: David,
:
: No experience with a T500.
:
: Note that there are a variety of LED backlights. The easy one is
: "white" LEDs with poor color. They basically use a blue (or
sometimes
: UV) LED with phosphor coatings to get white light. Typically they
: have poor color (peaks in blue and red and relatively less green).
: There are better white LEDs with a wider color gamut - this allows
: the screen to display more colors correctly. Most white LED screens
: cannot represent the full color space.
Overall, I'm sold on the idea of the LED backlights... Longer battery
life, longer laptop life; but I work a lot in Photoshop and color
accuracy
is a big deal for me.
From what it sounds, the blue tinting may be a problem for those
trying to
keep accurate color representation in their work. Can this problem be
overcome with monitor calibration and profiling or is it too
significant?
Jace
Note that I'm a pessimist so be warned. I also do NOT do color critical
work as I'm a more an engineer/physicist who works in the measurement
of light (radiometry), typically as applied to precision optical sensors
for remote sensing from spacecraft or aircraft.
I'm my opinion, no laptop display is good enough for critical color
work.
Long winded explanation follows :-)
Most laptop display panels are only 6-bit at the hardware level even
though they "support" 24-bit color which would be 8-bit per color.
The 17" HP DreamColor notebook panel is a true 8-bit per color panel.
There may be others but the information is not easy to find and I could
find no other true 8-bit per color panel when I was looking for a new
notebook about a year ago.
Panels built for color critical work are 10-bit per color (or more) at
the
hardware level and at the input. This might be referred to as 30-bit in
the marketing literature. The lookup tables and internal processing on
color critical panels is done at at least 12-bit (or more) to ensure
color
accuracy. With accurate processing and wide color gamut (say more
than 100% of which ever measure you are using), then the color
representation will be "good".
The next problem with notebook displays is the poor off-axis performance
of the current notebook screens. Some older Thinkpads (including my now
ancient T43p) had LCD screens with adequate off-axis performance.
By that I mean that the color stayed relatively constant with change in
view angle and the brightness didn't change too much. Very few (if
any) current laptop screens have adequate off axis performance for
good color, especially up/down. Many (but not all) good color LCD
screens use some variant of IPS for the LCD - they cost more and
are typically slower than many other types. My old T43p has an
IPS screen (Flexview in IBM/Lenovo marketing speak). Last year
I could find no IPS based notebook screens - they may exist but
they sure are hard to find if they do. Note that the expensive
color critical LCD monitors almost always state the type of panel
used (IPS for the HP DreamColor and same for the NEC panels
called SpectraView that are shipped with color calibrators).
Note that stated angles for various different types of panel are,
in many cases, measured differently so they are not directly
comparable with the given information. More marketing drivel
to make a true comparison difficult. Don't get me started on
contrast ratio as advertised by flat panel TV manufacturers.
Another problem is the color you see is a combination of
what is coming from the backlight through the LCD and
the ambient room light (or worse daylight). All panels
reflect some light depending on the surface of the LCD
and cover (if any) and the quality and type of anti-reflective
and anti-glare surface treatment. (For example, a high
quality optical window without anti-reflective coating when
in air/vacuum reflects between 4 and 5% of the light incident
on it at EACH surface. The actual amount depends on the
type of glass (really the refractive index of the glass). Very
high quality AR coatings can reduce this over the visible
spectrum but these coatings are not perfect and the AR
performance is not spectrally flat and it changes with
angle. Both surfaces of any "window" need coating unless
the second surface is bonded to the actual LCD surface with
index matching material. So if the monitor has a cover over
the actual LCD (many do) you can get reflections from the
front and back of the cover and from the LCD itself. That
adds up, especially for those awful (in my opinion) "glossy"
screens touted for image viewing.
That is why monitors for color work are typically
sold with shields to reduce the amount of light falling
on the monitor from the "room".
You also need to keep any screen clean to reduce scattering
from surface contaminants (fingerprints, dust, etc). Many
AR coating make the surface hard to clean and you should
not scratch any AR coating (they are typically softer than
the surface).
Sorry if this is too long :-)
Stuart
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