RE: show a PDF pop-up based on the viewer's zoom value ?

Subject: RE: show a PDF pop-up based on the viewer's zoom value ?
From: "Combs, Richard" <richard -dot- combs -at- Polycom -dot- com>
To: <monique -dot- semp -at- earthlink -dot- net>, "techwr-l" <techwr-l -at- lists -dot- techwr-l -dot- com>
Date: Mon, 8 Mar 2010 16:43:56 -0700

Monique Semp wrote:

> I have an odd little tool, FlowBreeze, that uses the native drawing
> in Excel to create the flowcharts. The tool has an image save export,
> which I use to create JPGs for (auto-generated-from-source-code) HTML
> docs. But for the FrameMaker-to-PDF guides, I need higher-res images
> course.
> Here's where FlowBreeze fails: its PNG image exporter is only 96 dpi.
> what I've been doing is turning off the grid lines and then using
SnagIt to
> capture the scrolling Excel window (because the flowcharts don't fit
on one
> viewable screen) at 300 dpi and then save as a PNG.

I don't want to go into a long lecture on graphics right now (and others
are better qualified to do so in any case), but the dpi settings you
assign when the image file is created are merely hints. They actually
have no effect on the image at all. Regardless of whether you set it to
96 or 300 dpi, the image is going to be X pixels wide by Y pixels high.

Of course, when you import the image into FM, you can scale it. And when
you display the output PDF, you can scale it again via the zoom setting.
Whenever that fixed X pixels by Y pixels image is scaled so that it uses
more or fewer than X pixels by Y pixels on the screen, either pixels get
discarded or added (by interpolation). When you scale to 50% or 200%,
the results aren't too bad. But when you scale to some arbitrary value
(like 71% or 114%) that doesn't permit simple division or multiplication
of pixels, it can get ugly.

The only reason PNG looks better than JPEG (at the same settings) is
because the latter is a lossy format optimized for photos
(continuous-tone images), which tends to give text and line drawings a
"smudged" look even before you introduce scaling issues. PNG is far
preferable for screen captures, flowcharts, or anything containing text
-- but that has nothing to do with the 300 dpi setting you made in

> And I've seen this problem (images in PDFs appear fuzzy at some zoom
> but not others) with images created all in vector formats by a variety
> tools (Illustrator, Visio, etc.). Isn't this just a PDF viewing

Vector formats contain no pixel information and can be scaled to any
size without any loss of resolution. If you've seen fuzzy Visio and
Illustrator images in PDFs, either they were exported from Visio and
Illustrator in a bitmap format (commonly done with Visio) -- or we have
very different definitions of fuzzy. ;-)

Richard G. Combs
Senior Technical Writer
Polycom, Inc.
richardDOTcombs AT polycomDOTcom
rgcombs AT gmailDOTcom


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RE: show a PDF pop-up based on the viewer's zoom value ?: From: Monique Semp

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