Re: [docbook-apps] Images in PDF appear too large

["Chris Chiasson" <chris@chiasson.name>]

There is actually another layer of subtlety to the 96 dpi setting. If
you are running MS Windows, it is likely that Windows is assuming that
your monitor+resolution combination actually gives 96 dpi.

ie, 1280x1024 at 96 dpi means Windows is assuming your monitor is
(1280/96=13.33) inches by (1024/96=10.66) inches in active display
area (with a sqrt(13.33^2+10.66^2)=17.08 diagonal measurement)

If this assumption isn't correct, everything that is displayed on your
screen is probably the wrong size.

I wrote a tutorial on correcting this for another mailing list if you want it.

On 4/27/07, T.G. Mutato <throw6617@gmail.com> wrote:
> Hi Chris,
>
> Two things come to mind:
>
> (1) Since I'm specifying the size of the image *in pixels*, it would
> seem that FOP should respect that and not scale the image based on
> dpi. For screenshots especially, it's easy to see the pixel dimensions
> of an image right from the desktop -- but dpi? And what's the point of
> specifying image dimensions in pixels (like you do for html) if FOP is
> going to ignore them anyway.
>
> (2) The FOP 0.93 documentation says it ignores dpi (which is
> apparently not accurate):
> "Some bitmapped image file formats store a dots-per-inch (dpi) or
> other resolution value. Since PDF and most output formats do not have
> a concept of resolution, but only of absolute image units (i.e.
> pixels) FOP ignores the resolution values as well. Instead, FOP uses
> the dimensions of the image as specified in the fo:external-graphic
> element to render the image." From
> http://xmlgraphics.apache.org/fop/0.93/graphics.html#resolution.
>
> I think the bottom line here is that specifying pixel dimensions (if
> you want to display an image "as-is") isn't too useful with FOP since
> there's no way to way to tell FOP to ignore the dpi info. So far just
> setting the dpi to 96 in the image files themselves seems to be the
> only way to get them to display properly.
>
> On 4/27/07, Chris Chiasson <chris@chiasson.name> wrote:
> > Assuming the matrix of pixels for an image is fixed, changing the dpi
> > of the picture is like telling the receiving application that the
> > image takes up different physical sizes:
> >
> > example:
> > A 100 pixel by 100 pixel picture at 100 dpi (in both horizontal and
> > vertical directions) = 1 inch by 1 inch picture.
> >
> > Supplying the same pixels and saying the picture is at 300 dpi will
> > give a 1/3 inch by 1/3 inch picture.
> >
> > This doesn't happen in web browsers because they ignore picture dpi, AFAIK.
> >
> > So, it makes sense that your 300 dpi picture is smaller if it has the
> > same pixel content as the other pictures.
> >
> > I assume you already knew all of this and that the scaling attributes
> > of DocBook are confusing to you. In that case, can we start over? I am
> > lost.
> >
>
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-- 
http://chris.chiasson.name/