Re: PDF xxx in screens

Subject: Re: PDF xxx in screens
From: "Huber, Mike" <mrhuber -at- SOFTWARE -dot- ROCKWELL -dot- COM>
Date: Fri, 31 Oct 1997 09:08:59 -0600

Don't give the virus writers more credit than they deserve. This would
be an extremely difficult hack, with a limited payoff. A virus would be
more likely to just mess up the graphics completely.

Far too many computing problems are blamed on viruses.

Sounds to me like there are problems with the way the software is
reducing the graphic. My clue is that, when use a lot of pixels, either
by printing (higher res than the screen) or by viewing at 200%, the
problems go away.

The X's
My guess is that the original gray is dithered. Reducing an image that
is dithered often results in unwanted patterns. The reduction applies a
pattern to the dithering pattern, giving a third pattern. The first two
patterns are designed not to be noticable, but the resulting pattern is
an accident. The human mind is very good at picking up patterns, so a
pattern that isn't designed to be unnoticed is very likely to be
noticed.

The letters
In the reduced view, each stroke in the font is a non-integer pixel
width. Maybe a pixel and a half wide. So, depending on the exact
position on the graphic, the viewer draws the stroke either one pixel
wide or two pixels wide. Where it's two pixels wide, it looks bold.

>-----Original Message-----
>From: Dave Chisma & Gail Hodgson [SMTP:chisma -at- c031 -dot- aone -dot- net -dot- au]
>Sent: Thursday, October 30, 1997 11:56 PM
>To: TECHWR-L -at- LISTSERV -dot- OKSTATE -dot- EDU
>Subject: Re: PDF xxx in screens
>
>Sonja Draeger wrote:
>...
>> I have screen captures in .wmf that I import to Word97. I make them =
>> grayscale, then convert the file to .pdf. When they get to .pdf, =
>> although they print great, they look disgusting on the screen. I have =
>> rows and rows of little xxxxxxs wherever the screen is gray. The font is =
>> all blotchy and bumpy, like some part of the letters are bold and some =
>> are not. I have to view the .pdf file at about 200% before you can =
>> actually read the text.
>...
>Hi Sonja,
>
>It sounds like you have a virus!!!. Better try Vet. ;-)
>
>

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