Re: ATM Laptop Screen Covers

["Andrew Schott" <aschott@cfl.rr.com>]

Halftone screens may not be desireable for the darkening of laptop screens
due to the problem of aliasing between the pitch of the screen dots and the
pixels in the LCD display.  You would have to use extremely fine pitch
screens to avoid gross moire patterns in the display.  Most laptops have a
screen resolution approaching .25 dot pitch which translates to something
like 102 lpi.  The moire pattern frequency would be the diffference between
the screen and the display.  65 lpi screen would present a 1.5 cycles per
inch pattern across the screen that would be really annoying.  To reduce the
moire to something unnoticeable, the difference would have to be high enough
to raise the frequency to something near the original display resolution
requiring a screen of 10,400 lpi or so.  A continuous tone filter would be
much more desireable when used with something that has a grid pattern in it
already like a CRT or a LCD panel.

Maybe there's a positive side to moire patterns over your star maps but I
can't see it.


----- Original Message -----
From: "macaddicted" <daviddesign@mac.com>
To: "ATM List" <atm@shore.net>
Sent: Wednesday, August 29, 2001 4:37 PM
Subject: Re: ATM Laptop Screen Covers


>
> > I have used a large piece of polarizing screen (transmits
> > about 30%) but are there any cheaper alternatives to this?
>
> Well, since everybody is going to the printer supply shop anyway...
>
> You might try getting a sheet of screen material. It is used to put a gray
> into an image that would otherwise print black. I have no idea what its
cost
> is relative to polarizing screens because I never have to buy it- my
printer
> always takes care of it.
>
> Because you are working with a negative process you would need to get a
> screen that gives you a lighter print (on a press). For example a 10%
screen
> blocks 90% of the image (to give you a 10% finished product). The
screening
> material uses a halftone screen of varying resolution. A newspaper is
around
> 65lpi (lines per inch), a typical magazine is the 100lpi range (depends on
> the quality of the paper), a high end color book or magazine will be
around
> 150-200lpi. The higher the lpi the smaller the dot. And no, lpi and dpi
are
> not the same thing.
>
> You can try making your own screen with a laser printer (this won't work
as
> well on an inkjet because of the way the ink is put down by the printer).
> Just fill an entire page with a box filled with a grayscale at the level
you
> want as the final darkness (in this instance you are doing a positive, so
> the explanation above does not apply). If you have software that will
allow
> you to set the output resolution (Quark, PageMaker, InDesign and some
lower
> end graphic design programs do- Corel might, though I am not sure) set it
> for as high a line screen as you can, though even the best laser printers
> usually cannot go beyond about 100lpi. Print the page on a sheet of
acetate
> (overhead film).  Viola, you've got it. Whether it will do what you want
is
> another question.
>
>
> Dave
> Macaddicted
>
>
>