Frederick said:
I have a flat screen monitor NEC L1550V whose manual says one of its
resolutions is 1024X768. That sounds digital to me. I thought since
its only input is VGA that it is analog.
???
Thanks
Big Fred
If you use Monitor Asset Manager (moninfo) from entechtaiwan.com,
it shows the resolutions too. This is what my monitor shows
(native format being 1280x1024). The program can actually
probe the EDID table from the monitor, to get these values.
Standard timings supported
720 x 400p at 70Hz - IBM VGA
640 x 480p at 60Hz - IBM VGA
640 x 480p at 67Hz - Apple Mac II
640 x 480p at 72Hz - VESA
640 x 480p at 75Hz - VESA
800 x 600p at 56Hz - VESA
800 x 600p at 60Hz - VESA
800 x 600p at 72Hz - VESA
800 x 600p at 75Hz - VESA
832 x 624p at 75Hz - Apple Mac II
1024 x 768p at 60Hz - VESA
1024 x 768p at 70Hz - VESA
1024 x 768p at 75Hz - VESA
1280 x 1024p at 75Hz - VESA
1152 x 870p at 75Hz - Apple Mac II
1152 x 864p at 75Hz - VESA STD
1280 x 1024p at 60Hz - VESA STD
The 1024x768 is a VESA resolution (VESA is a standards body).
The "p" stands for progressive, since LCD displays are normally
progressive scan for computer monitors. If the letter "i" was there,
that would be interleaved, meaning there are odd and
even frames being displayed in succession. Interleaved,
is what an old television used.
There are multiple entries, because the display supports
"multisync" and operates at more than one resolution. At
the LCD panel itself, it supports only one resolution, the
"native" resolution of 1280x1024. There are actually 1280
columns by 1024 rows of pixels, switched on and off. The
intensity of a pixel, might be adjustable with a 6 bit or
an 8 bit number for each color.
The other resolutions are achieved by "scaling" the image to
fit the native resolution. The image doesn't look as sharp
at the non-native resolution, due to the scaling process.
In terms of refresh rates, the panel has limits on that too.
One of the sites, perhaps Xbitlabs, claims when operating at
a higher refresh rate, the panel throws away "1 in N" frames,
to drop the actual refresh rate down to 60Hz. But some modern
panels (more modern than mine), support higher refresh rates
than that, so may not need to throw anything away.
These are the processes possible on the display path. DAC
is digital to analog conversion. ADC is analog to digital
conversion. Scaling is still needed on the VGA path, because
the number of rows of pixels and the number of scan lines,
don't match.
<--- Video card ----> <------ LCD monitor ------>
GPU (digital) --- DAC --- analog,VGA --- ADC --- scale --- raw_panel
GPU (digital) ----------- digital,DVI ---------- scale --- raw_panel
The digital path would be "perfect", if the scaling step could be
skipped, and if you select the native resolution value, which
in my case is 1280x1024, then no scaling is needed and the scaler
disappears from the picture. In the analog path, if you select
native resolution, there is still some room for color inaccuracy
due to the DAC and ADC steps. But the human eye is so accommodating,
you'd hardly notice.
*******
Inside the raw_panel, there are more analog processes involved.
http://en.wikipedia.org/wiki/TFT_LCD
"The column and row wires attach to transistor switches,
one for each pixel. The one-way current passing characteristic
of the transistor prevents the charge applied to the pixel from
draining between refreshes to the display image. Each pixel is
a small capacitor with a layer of insulating liquid crystal
sandwiched between transparent conductive ITO layers."
So there's "lots of digital *and* analog" in that picture. The
capacitor for each pixel, holds an analog voltage level.
HTH,
Paul
