[GRASS5] PNG driver problem

Glynn Clements glynn.clements at virgin.net
Tue Aug 24 02:49:57 EDT 2004

Hamish wrote:

> > BTW, the latest CVS version of the PNG driver has an option to write
> > the image file after each command. This eliminates the need to stop
> > and re-start the driver in order to get the image. It also allows you
> > to create (binary) PPM images as an alternative to PNG.
> What's the advantage of PPM? Less CPU overhead, but less throughput than
> TIFF? (so the best solution for display apps where storage space isn't
> an issue but CPU is)

PPM's main advantage is simplicity. Adding the code to write a PPM
image was a couple of minutes work. Writing a reader is almost as
trivial. One consequence of this is that it's widely supported.

> Will Tcl output to PNG? It would be nice for the NVIZ image dump menu to
> include that so we don't have to run pnmtopng every time.. JPEG?

My photo(n) manpage (from 8.0) says that Tk supports reading and
writing PPM and GIF images, although it's possible that other formats
have been added in later versions.

However, that isn't relevant to NVIZ. NVIZ supports PPM and TIFF
because the OGSF library includes functions to write those formats
(gsd_img_ppm.c and gsd_img_tif.c); it doesn't use Tk's image support.

> Winding further off topic, does dumping a max. res PPM work for anyone
> on MacOSX from NVIZ? not me, I just get the bits.

Can you elaborate?

Glynn Clements <glynn.clements at virgin.net>

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