Re: dashed lines with GD [ was Re: symbol/color/line consistency in terminals]

[Pierre <pie...@gm...>]

On 2/13/07, m sutton <mw...@us...> wrote:
>
> > ----- Original Message -----
> > From: "Ethan A Merritt" <merritt@u.washington.edu>
> > To: gnu...@li...
> > Subject: Re: dashed lines with GD [ was Re: symbol/color/line consistency in  terminals]
> > Date: Sun, 11 Feb 2007 21:44:45 -0800
> >
> >
> > On Sunday 11 February 2007 21:25, Daniel J Sebald wrote:
> > >
> > > > However, it would be nice to set DPI somehow through GD.  > It
> > > would simplify things when I import images into Word or
> > > PowerPoint. Well, that isn't too difficult, is it?
> >
> > Actually, it is.
> >
> > The PNG standard does not provide a place to store dpi.
> > Some apps store it in a comment record, but that is idiosynchratic,
> > and anyhow gd does not (yet) support comment records in PNG.
> >
>
> OK so it not DPI but its close.
>
> The PNG specification supports a chunk called pHYs which related pixels to phyiscal dimensions.
>
> LIBPNG has the following:
>     png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
>         unit_type);
>     res_x       - pixels/unit physical resolution
>                   in x direction
>     res_y       - pixels/unit physical resolution
>                   in y direction
>     unit_type   - PNG_RESOLUTION_UNKNOWN,
>                   PNG_RESOLUTION_METER
>
> So it would appear the GDLIB could would need to a way to call png_set_pHYs.  Then modify gd.trm to accept a resolution setting.
>
> Mike Sutton
>
> p.s.  As a temporary workaround I run ImageMagick's convert with the -density option to set resolution.

The DPI/resolution is a purely informative data. A pixel remains a
pixel. A software can take care of it or not, applies its own, etc (I
had all kind of troubles in pre-press while trusting this info too
much). So I would take it with a grain of salt :)

About GD and meta data, I would like to provide some bridges between
GD and a (working) meta library with a permissive enough license. At
the very least, if nothing exists, I will go with a GD specific
implementation.

--Pierre