Re: [hpoj-devel] OJ 700 Progress

[Robert G. B. <rg...@ph...>]

On Tue, 13 Feb 2001, Gerhard Fuernkranz wrote:

> David Paschal wrote:
> >
> > James Klicman wrote:
> > > I have succeeded in scanning BILEVEL_THRESHOLD/NO_COMPRESSION
> > > and then creating a viewable .pgm file with the data.
>
> A very simple, easy graphics file format.
> Actually it is a whole family consisting of
>
> "pbm" -> bitmap with depth=1, each pixel can be
>          black/white (-> e.g. a typical Fax)
> "pgm" -> a grayscale picture
> "ppm" -> a RGB color picture (truecolor with RGB
>          for each pixel, not with colormap/indexed
>          like a GIF)
> "pnm" -> used to denote the family, i.e. any of
>          the above three
>
> There also exist the pbmplus tools for manipulating
> these file types, see /usr/X11R6/bin/*{pbm,pgm,ppm,pnm}*
>
> Gerhard

Indeed, a lot of those tools are already in place and automatically used
in the printer filters, at least for a RH system.  Once you get it into
a p?m format, you have a number of tools for scaling, rotating, and the
like.  RH's strategy appears to be "get an arbitrary format into pnm,
then convert pnm to ps, then print (usually using ghostscript printer
filters)."  See:

rgb@ganesh|T:120>dir /usr/lib/rhs/rhs-printfilters/
bmp-to-pnm.fpi*  gif-to-pnm.fpi*  pnm-to-ps.fpi*   tiff-to-pnm.fpi*
dvi-to-ps.fpi*   jpeg-to-pnm.fpi* rast-to-pnm.fpi* troff-to-ps.fpi*

where in these filters many of the tools are demonstrated in pipes.

A single example.  If you have a digital camera and take a lot of
pictures, you probably want to turn the hi-res jpegs into low-res,
rescaled, possibly rotated gifs to stick up on your website.  Here is a
fragment from a little perl script I wrote to help me make this
conversion:

 $command = "cat $INFILE | djpeg -pnm | pnmscale $scale | pnmrotate $rotate | ppmquant 256 | ppmtogif - > $OUTFILE";
 if($verbose){ print "$command\n"; }
 system($command);

djpeg converts jpeg to pnm (among others -- it will convert straight to
gif but not allow scaling and rotation).  pnmscale and pnmrotate scale
and rotate the "pixel any map" (pnm). ppmquant fixes the colormap depth
-- useful if you don't want to exhaust the colormap of a low-res 8 bit
display on an unknown browser somewhere.  Finally ppmtogif does the
final conversion to gif.  Using a tool like this (with obvious perl
wrapping it and setting the variables, full program available on
request) allows one to convert a whole directory of jpegs with a simple
shell loop, and is often a lot easier and faster to use than cranking up
a whole GUI (e.g. xv or eeyes or gimp or whatever) just to do a simple
rotation and scaling.

   rgb

-- 
Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rg...@ph...