Changing Image Resolution

[Abe Gillespie]

The displaying's not the problem.  You need the printer to print it
correctly.  The header in the PNG file is what controls the DPI (at
least as far as I can tell).

-Abe

On 12/14/05, Mark Wright <sparkymeister at gmail.com> wrote:
> Could you have mapserver create a 600x400 image and display it at 300x200?
>
>
> Mak
>
> On 12/14/05, David Bitner <osgis.lists at gmail.com> wrote:
> > In general, what would it take to add some parameters to the mapfile
> > that allow for better resolution control.  Right now I have mapscript
> > code that goes through and adjusts the sizes of all my symbols and
> > fonts (of course bitmap symbols wouldn't work) for different
> > resolutions, but I would love to see this as more meaningful
> > resolution parameters in the mapfile that could be controlled through
> > cgi.
> >
> > I would also love to see another setting that would use certain
> > resolutions (as above) at certain image sizes.  If you set this up
> > correctly, it would allow for better easy use of WMS layers in client
> > applications as while browsing the image on the screen it would use
> > the low res, but as soon as the client application makes a request for
> > a huge image, it would be able to tell that you were creating a
> > printout and could rescale all the symbols so that what you printed
> > would be the same as what you had on your screen.
> >
> >
> >
> > On 12/14/05, Abe Gillespie <abe.gillespie at gmail.com> wrote:
> > > I know it's impossible to change DPI on-the-fly within MapServer (it's
> > > set at compile time).  But I want to "fake" a higher resolution image
> > > within PHP.
> > >
> > > Let's just use PNG as an example.
> > >
> > > I assume there's a header in the PNG image that specifies its DPI so
> > > this info can be used by printers, image editors, etc.  So my idea is
> > > if I want a PNG with twice the resolution (from 72 to 144 DPI) is to
> > > simply adjust the width & height in MapServer and then edit the PNG's
> > > header in PHP.
> > >
> > > So, if I have a 300x200 pixel image, but I want to increase the DPI to
> > > 144:  First I'd change MapServer width & height:
> > >
> > > $map->setSize(600, 400);
> > >
> > > Then I'd render the image to disk, open the file up in PHP, and change
> > > the header with some binary file operations.
> > >
> > > Is my thinking correct here?  If so, are there any examples of binary
> > > file manipulation via PHP.  Are there any examples of the PNG's
> > > header?
> > >
> > > Thanks for the help.
> > > -Abe
> > >
> >
>
>
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