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Re: [docbook-apps] excluding image format according to output


Hi Dave,

On Sun, Apr 17, 2005 at 11:57:45AM +0100, Dave Pawson wrote:
> On Sun, 2005-04-17 at 09:28 +0930, Paul A. Hoadley wrote:
> > To keep it simple, I'll stick with line drawing diagrams as the
> > type of image, since the considerations are probably different for
> > different image types (such as photographs, screenshots, and so
> > on).
>
> So down to vector images, on fo output?

For images like line drawings and diagrams, I'd have to say yes.  But
I suppose you also need to consider the intended use of the final
document.  If you're publishing a lecture hand-out, a PNG or GIF might
be perfectly acceptable, particularly if it has not been scaled.  If
you're intending to print a book, you would need to use a vector
format.

> This does narrow down doesn't it!  Is SVG the only viable vector
> format for HTML then?  Still restricted to a browser plug in.

As far as I know, yes.

> > If the output format can handle it, you are certainly better off
> > using a vector format for the image (EPS, SVG, PDF).
>
> Again showing my ignorance. EPS I knew of, SVG I'm OK with, but PDF
> for an image?

Sure.  PDF is just a page description language, after all.  XEP, for
example, can include PDF images in a PDF just using the
fo:external-graphic element.  Think including EPS in PS.

> What tools are used to generate them please?

I have actually never used Adobe Illustrator, but I'd be surprised if
you couldn't output a drawing directly as a PDF.  XFig will export as
PDF.  Failing that, save your image from your favourite vector drawing
program as EPS and use ps2pdf to convert.

> Do they open in Acrobat reader as any other file?

Yes.

> > The main issue is scaling.  Say your printer can print 600x600
> > DPI, and you have a 2 inch square region on your page for a
> > diagram.  An EPS image will be rasterised into a 1200x1200 bitmap
> > to be placed in that region.  Now, if you had a 1200x1200 PNG of
> > your diagram, the output would be essentially the same.
>
> PNG isn't a vector format though Paul... is it?

No, it's not.  I probably wasn't completely clear there.  Say that you
know your final output needs to be 2 inches square on a 600x600 DPI
printer.  You need a 1200x1200 image.  You could create an EPS
version, and on output it would be rasterised to a 1200x1200 bitmap
for printing.  Theoretically, you could produce _exactly the same_
bitmap as a PNG.  But if you did that, and later needed to put it in a
4 inch square region, the scaled result will look blocky.  The EPS
image will be re-rasterised to 2400x2400 bitmap with no loss of
quality.


-- 
Paul.

w  http://logicsquad.net/
h  http://paul.hoadley.name/

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