[RTTY] Article on LCD Displays

[Kok Chen]

On Nov 11, 2004, at 12:57 AM, Ian White, G3SEK wrote:
> It's an interesting article, but misleading about the "density" of the 
> display. Screen sizes and numbers of pixels are going up, but the 
> physical density of the TFT pixels remains stuck around 0.2-something 
> millimetres.

Ian is right, the best LCD panels available today (panels in the high 
end Dell laptops, for example) are at about 140 dpi (0.18 mm pitch), a 
few years ago, most LCD were at 90 dpi or so.

But that is not too horribly bad assuming that you don't put your nose 
right against the display.  Most LCD panels are at about 100 dpi.  
(Remember when CRT were at 72 dpi?  -- thus the old 72 dpi standard 
used in desktop publishing.)

Human vision has an angular resolution of at best 50 cycles (one cycle 
is two pixels) per degree.  This is from the Weber Contrast Sensitivity 
curve for luminance (color resolution is 2 to 3 times worse, depending 
on which opponent colors are involved).  Once we get there, any 
additional device resolution is wasted.

One of the reasons the LCD manufacturers are holding back on increasing 
the resolution is that operating systems don't yet have variable 
resolution built in.  Yes, you can change fonts in an app, but things 
like the menu bar and icons do not scale easily (you want to scale so 
icons get bigger but hairlines remain hairlines, for example).  This 
will change in the next one to three years.  As it is, increasing 
display resolution will make things too darn small to see -- take a 
look at the tiny stuff on the desktop of the aforementioned Dell.

Another factor that drives the market is that TVs don't need that many 
pixels.  Even the highest ATSC HDTV resolution in the US calls for only 
1080 pixels in the vertical dimension and 1920 pixels horizontally.  
You view a TV further than a computer display, so no one complains 
since Weber's contrast curves takes over.

If you are in a stickler for sharpness, you'll need to buy displays 
with a "digital" interface (DVI).  Most of the cheaper panels are 
analog displays where you send the usual H-sync V-sync and analog 
voltages and the displays recovers the rows and columns of pixels from 
that.  You lose a little since you can't precisely recover the pixel 
registration.  The DVI displays send pixels as a digital data stream 
and each one is deposited right smack on the proper pixel on the panel. 
  Be prepared to pay a higher price and you will also need a video 
"card" that can drive them.  Most of the "digital" panels will also 
take analog input, but you will be wasting hard earned money since they 
won't look any sharper when driven through the analog input.

73
Chen, W7AY