[Ham-Computers] RE: Analog vs Digital Flat Panel Displays - What's theDifference?

[Hsu, Aaron (NBC Universal)]

General pros and cons for CRT's and LCD's.

CRT's
-----
Inexpensive compared to LCD's.
Wider color gamut and more accurate colors.
More uniform colors across the screen.
Higher contrast than LCD's (black to white levels).
No color shift when viewing the screen at any angle.
Faster transient response - no "ghosting" on moving objects.
Excellent picture quality at any resolution (up to limits of monitor).


LCD's
-----
Smaller "footprint" and lighter than CRT's
Consumes less power (less heat generation and lower power bill).
Sharper than CRT (only) when used at "native" resolution.
No convergence errors (alignment between Red/Green/Blue)
Full viewable "glass" area - 17" really means 17" viewable area.
Higher "coolness" factor - "wow, you have a TFT flat screen"
Poor choice for fast moving objects due to slow transient response
(getting better these days).


So, in many respects, the CRT is still better when it comes to absolute
picture quality - something critical to people who work with graphics,
pictures, or colors as a profession (such as when using Pantone color
matching).  LCD's basic back-lighting techniques can not produce a
uniform brighness across the entire screen, so some areas are slightly
darker than others.  Also, LCD's suffer from viewing angle problems.
Due to the way LCD's work, if you shift your viewing angle, the picture
will change in brightness or shift in colors - with today's technology,
this can't be avoided.

Now LCD's do take up much less space, especially considering that an
LCD's viewable area is equivalent in size to the next larger CRT - a 17"
LCD equals a 19" CRT in viewable area.  And, they carry the "cooless"
factor, generate less heat, and consume less power.  However, when it
comes to picture "sharpness", always make sure you run an LCD at it's
"native" resolution" - this is the highest resolution the LCD supports.
Why?  Because an LCD has a fixed number of pixels.  If you run the LCD
at a lower resolution, then the picture is "scaled" to fit the full size
of the screen.  Unfortunately, LCD's, unlike CRT's, can't change the
size if their pixels, so the scaling creates "blocky" looking text.
Better LCD's and video cards will "smooth" out these blocks or the
jagginess, but CRT's excel here as it is not limited to a "fixed" number
of pixels.


OK, digital vs analog.  There's a very noticable difference if you know
what to look for.

Analog:
-------
Basically, analog VGA sends Red, Green, and Blue to the monitor using
voltage levels for each color.  The accuracy of the voltage levels
depends on the quality of the Digital to Analog Converter (DAC) in the
video card and the Analog to Digital Converter (ADC) in the display
(note that there are two conversions here).  There're also a two sync
signals to convert (twice).  In a perfect world, the DAC/ADC conversion
would be perfect and the decoded signals the display receives is an
exact copy of what the video card set.  However, we all know that analog
conversion processes are far from perfect.  This causes analog picture
quality to suffer a bit, but if the quality of the components is
maintained, excellent picture quality can be achieved.  High-end CRT's
designed for graphics professionals use high-quality ADC's to achieve a
more accurate picture.  Typical problems with the conversion process are
color/brightnes issues and "screen shift" (where the picture isn't
centered on the display).  This is why there are color, brightness, and
screen shift controls on analog monitors.

Digital:
--------
With a digital interface, the video card/adapter has direct 1-to-1
control of every pixel on the display.  All signals are sent digitally
(no conversion) to the display and, therefore, there's no conversion
loss.  Since there's no "sync" signal and the video adapter is
controlling each pixel directly, there are no screen shift or color
controls.  The brighness control on a TFT LCD is to adjust the backlight
and the contrast control generally determines maximum luminocity of each
pixel (luminocity might not be the right word, but I think you get the
general idea).  The overall picture quality of a DVI connected display
is much better than an analog connected display.

One of the best ways to "see" the difference is to view some sample
screens on a display that has both DVI and analog inputs.  The
difference is usually most noticable on high-resolution text screens
where characters are a single pixel wide or tall.  Vertical and
horizontal lines are also good test subjects.  Pictures are generally
not good subjects except to judge color.  Make sure that any text
"smoothing" is disabled before testing as this will introduce
intentional "artifical" artifacts to make text look smoother.  Also make
sure to adjust the analog picture as best as possible - sometimes, the
"auto adjust" works well here, but it might need a bit of tweaking.
Digital modes don't require adjusting except maybe for backlight
brightness and/or contrast.


Hope everyone is now more confused than ever <g>!  All in all, TFT's are
a good choice for most people as they take up less space and consume
less power.  You'll need to spend more money on a higher-end TFT if you
enjoy gaming or need better color reproduction.  CRT's are big, clunky,
and warm up your room, but are necessary for people where speed (gaming)
and color rendition (photo editing) are of utmost importance.

73 all!

  - Aaron, NN6O


-----Original Message-----
Sent: Tuesday, January 24, 2006 9:26 AM
Subject: [Ham-Computers] Analog vs Digital Flat Panel Displays - What's
theDifference?

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Dell has two main choices - analog and digital, with digital
considerably 
more expensive. What are the relative merits?  Presumably, digital has a

better "picture"; is that improvement mostly for photos, or does it help

with schematics, etc., available on the web.

When a FP is listed as a 17", does that mean a display with a 17"
diagonal 
measurement?  The diagonal CRT measurement on my 19" Dell is about 17
7/8", 
so I guess I would lose about an inch dropping from a 19" CRT to a 17"
flat 
panel.

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