Re: bitmaps in pdfs

Subject: Re: bitmaps in pdfs
From: "Brierley, Sean" <Brierley -at- QUODATA -dot- COM>
Date: Wed, 19 May 1999 10:48:19 -0400


Not to be flippant, but most of what you ask is best answered by formal
training. Scan your library or bookstores for info on these topics, visit
the STC site to see what it offers in the way of published material
( I don't really have time to organize my thoughts here,
so please bear with me and forgive me if I mis-speak. Any other whirlers
should feel free to correct any imprecise generalization I might make ;?).

Regarding your PDF issues, how do the graphics print? Do they print fine and
just look lousy? If so, it's a limitation of the Acrobat Reader viewing
software; live with it ;?(. Try zooming into the graphic, this should make
them look better. If the graphic prints as poorly as it looks, check that
PDF writer is set to produce 600 dpi resolution PDFs. Another route to go is
to buy the Acrobat 4 software package and use distiller or PDFMaker to make
your PDFs from Word. This'll give you better control.

About editing screen captures. These are bitmaps. Stay away from vector
image editors, such as CorelDRAW and Illustrator. Look to PhotoPaint,
PhotoShop, PhotoImpact, Paint Shop Pro, Picture Publisher . . . (uninstall
MS Paint). About using these products, training or time to learn is the key.
Bear in mind that what you want to do is resample. Simply saving between
bitmap formats using filters is not going to accomplish what you need. Look
for an Edit|Resample or Format|Resolution menu selection. Search the online

You might be better off with a screen capture utility like Snagit 32 from

Regarding changing the resolutions of bitmaps with paint software, consider
this: if you add or delete pixels you will reduce the crispness and clarity
of the bitmap. Unlike vector images, which are infinitely scaleable, bitmaps
do not resample well. If you take a 2x2 inch bitmap at 600 dpi and resample
it to 4x4 inches, the dpi reduces to 150, resulting in jaggies when
printing. To compensate, you can resample from 150 back to 300 dpi but, in a
4x4-inch image, you are going from 90,000 to 360,000 pixels, which means
your paint software has to guess at what (270,000) 360,000-90,000 pixels
look like. Paint software is generally quite good at this but you will lose
sharpness and clarity (you can use anti-aliasing to smooth things out but
this adds blurryness). You do have a better time reducing the area of an
image, as you often do with a screen capture. Going from a 4x4, 100 dpi
screen capture to a 2x2 image keeping the same number of pixels will result
in a 400 dpi image. However, if you want to resample the 400 dpi back down
to 100 dpi, you are removing pixels. Again, paint software is good at
guestimating which pixels need to go and what needs to change in the
remaining pixels, but you will lose clarity, sharpness, and encounter
blurryness by doing this.

Screen displays are typically considered to be 72dpi for the Mac and 96 dpi
for Windoze. That's why web sites viewed on macs display text larger than
the same site seen on a Windows machine.

When you perform a screen capture, the resolution and color depth of the
capture is initially that of your screen. For example, I use 24-bit color
and 1024x768 resolution on a 17-inch monitor. If I capture the entire
screen, I get a bitmap that measures 1024 pixels across, 768 pixels down,
and has RGB 24-bit color. Measure or calculate the actual inches across and
down of your monitor for an approximate dpi.

Think of dpi on screen as printing to a 96 dpi printer. The source may not
be 96 dpi but you only get 96 dpi worth of resolution. Thus, a photograph
scanned for a magazine at 2400dpi will display on-screen at 96 dpi but will
print in a glossy mag at 1800dpi.

For example, in my current position I don't produce color output or, for
that matter, neither do I need to output for offset press. I do, however,
have a requirement that my graphics print greyscale at 600dpi and also be
displayed on the internet or as PDFs. As a result, I resample my 24-bit
color screen captures to 256 colors, which produces acceptable greyscale
printed output and meets the 212-color requirement of the web and produces
acceptable color output for viewing in PDF.

Where was I, oh, yes, scan your library or bookstore for some info on all of
these subjects and, again, get a capture utility like SnagIt 32. Hope this

sean -at- quodata -dot- com

>>>-----Original Message-----
>>>From: Moore, Tracey [mailto:TMoore -at- PARKERVISION -dot- COM]
>>>Sent: Wednesday, May 19, 1999 10:02 AM
>>>To: TECHWR-L -at- LISTSERV -dot- OKSTATE -dot- EDU
>>>Subject: bitmaps in pdfs
>>>I've seen this discussed before, and I searched the archives, but the
>>>results I got didn't answer my question. I apologize for
>>>bringing this
>>>up again, please respond to me directly.
>>>I created a pdf using the PDF writer in Word. The doc
>>>contained a ton of
>>>screen shots. The pdf displays the screens shots very badly. They're
>>>almost unreadable. In Word they look great.
>>>I went to the Adobe web site and it said that screen shots
>>>exist in the
>>>wild at 72 dpi, and Word smoothes them out to look good, but pdf does
>>>not. Adobe says to lower your screen resolution before taking screen
>>>shots, then saving the screen shots at a minimum of 200 dpi.
>>>Well, I've tried redoing the screen shots using Corel Photo
>>>Paint, Corel
>>>Draw, PaintShopPro Image Composer and MS Paint. Nothing has
>>>helped. What
>>>I can't figure out is how to change the dpi settings at which the
>>>bitmaps are saved. The Save As and Export dialogs just say "save as"
>>>bmp, gif, tif, jpg, etc., nothing about changing the
>>>settings other than
>>>uncompressed to compressed.
>>>How do you save a bitmap at 200 dpi or higher from a screen
>>>shot (that
>>>is only 72 dpi anyway)?
>>>Thanks for your help!

From ??? -at- ??? Sun Jan 00 00:00:00 0000=

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