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Ppmshadow User Manual(0)                              Ppmshadow User Manual(0)

       ppmshadow - add simulated shadows to a PPM image

       ppmshadow [-b blur_size] [-k] [-t] [-x xoffset] [-y yoffset] [ppmfile]

       This program is part of Netpbm(1).

       ppmshadow adds a simulated shadow to an image, giving the appearance that the contents of the image float above
       the page, casting a diffuse shadow on the background.  Shadows can either be black, as cast by opaque  objects,
       or  translucent,  where the shadow takes on the color of the object which casts it.  You can specify the crisp-
       ness of the shadow and its displacement from the image with command line options.

       ppmshadow sees your image as a foreground on a background.  The background color is whatever color the top left
       pixel  of your image is.  The background is all the pixels that are that color and the foreground is everything
       else.  The shadow that ppmshadow generates is a shadow of the foreground, cast on the background.

       The shadow is the same size as the foreground, plus some fringes as determined by the -b option.  It  is  trun-
       cated to fit in your image.  The output image is the same dimensions as the input image.

       You  can use pamcomp to place a foreground image over a background before running ppmshadow on it.  You can use
       ppmmake to make the background image (just an image of a solid color).

       -b blur_size
              Sets the distance of the light source from the image.  Larger values move the light source closer, cast-
              ing  a  more  diffuse  shadow,  while  smaller  settings move the light further away, yielding a sharper
              shadow.  blur_size is the number of pixels of fringe there is on the shadow,  beyond  where  the  shadow
              would be if there were no blurring.

              The default is 11 pixels.

              Note that this option controls only the fringing effect of moving the light source closer to the object.
              It does not make the shadow grow or shrink as would happpen in the real world if you moved a point light
              source closer to and further from an object.

       -k     Keep  the  intermediate  temporary  image  files.  When debugging, these intermediate files provide many
              clues as to the source of an error.  See below  for a list of the contents of each file.

       -t     Consider the non-background material in the image translucent -- it  casts  shadows  of  its  own  color
              rather than a black shadow, which is default.  This often results in fuzzy, difficult-to-read images but
              in some circumstances may look better.

       -x xoffset
              Specifies the displacement of the light source to the left of the image.   Larger  settings  of  xoffset
              displace  the  shadow  to the right, as would be cast by a light further to the left.  If not specified,
              the horizontal offset is half of blur_size  (above), to the left.

       -y yoffset
               Specifies the displacement of the light source above the top of the image.   Larger  settings  displace
              the shadow downward, corresponding to moving the light further above the top of the image.  If you don't
              specify -y, the vertical offset defaults to the same as the horizontal offset (above), upward.

       Input is a PPM file named by the ppmfile command line argument; if you don't  specify  ppmfile,  the  input  is
       Standard Input.

       The output is a PPM file, written to Standard Output.

       ppmshadow  creates  a  number  of  temporary  files  as  it  executes.   It  creates  a new directory for them,
       /tmp/ppmshadowpid, where pid is the process ID of the ppmshadow process.  If the TMPDIR environment variable is
       set, ppmshadow creates the directory there instead of /tmp.

       In  normal  operation, ppmshadow deletes each temporary file as soon as it is done with it and leaves no debris
       around after it completes.  To preserve the intermediate files for debugging, use the -k command line option.

       The temporary files are:

              A copy of the input.

              Positive binary mask

              Convolution kernel for blurring shadow

              Blurred, colored shadow image

              Blurred shadow image before coloring

              Clipped shadow image, offset as requested

              Blank image with background of source image

              Offset shadow

              Inverse mask file

              Just the foreground.  Rest is black.  Original image times inverse mask.

              Generated shadow times positive mask

              Everything but the foreground (foreground area is black).

       The source image must contain sufficient space on the edges in the direction in which the  shadow  is  cast  to
       contain  the shadow -- if it doesn't some of the internal steps may fail.  You can usually expand the border of
       a too-tightly-cropped image with pnmmargin before processing it with ppmshadow.

       Black pixels and pixels with the same color as the image background don't cast a shadow.  If this causes  unin-
       tentional  'holes'  in  the shadow, fill the offending areas with a color which differs from black or the back-
       ground by RGB values of 1, which will be imperceptible to the viewer.  Since the comparison is exact, the modi-
       fied areas will now cast shadows.

       The  background  color  of the source image (which is preserved in the output) is deemed to be the color of the
       pixel at the top left of the input image.  If that pixel isn't part of the background, simply add  a  one-pixel
       border at the top of the image, generate the shadow image, then delete the border from it.

       If  something  goes  wrong  along  the way, the error messages from the various Netpbm programs ppmshadow calls
       will, in general, provide little or no clue as to where ppmshadow went astray.  In this case,  Specify  the  -k
       option  and examine the intermediate results in the temporary files (which this option causes to be preserved).
       If you manually run the commands that ppmshadow runs on these files, you can figure out where the  problem  is.
       In  problem cases where you want to manually tweak the image generation process along the way, you can keep the
       intermediate files with the -k  option, modify them appropriately with an image  editor,  then  recombine  them
       with the steps used by the code in ppmshadow.

       See  the  ppmshadow.doc  file in the Netpbm source tree for additional details and examples of the intermediate
       files and debugging ppmshadow.

       Shadows are by default black, as cast by opaque material in the image occluding white light.  Use the -t option
       to simulate translucent material, where the shadow takes on the color of the object that casts it.  If the con-
       trast between the image and background is insufficient, the -t option  may  yield  unattractive  results  which
       resemble simple blurring of the original image.

       Because  Netpbm used to have a maximum maxval of 255, which meant that the largest convolution kernel pnmconvol
       could use was 11 by 11, ppmshadow includes a horrid, CPU-time-burning kludge which, if a blur of  greater  than
       11  is requested, performs an initial convolution with an 11 x 11 kernel, then calls pnmsmooth (which is itself
       a program that calls pnmconvol with a 3 x 3 kernel) as many times as the requested blur exceeds 11.  It's ugly,
       but it gets the job done on those rare occasions where you need a blur greater than 11.

       If  you  wish to generate an image at high resolution, then scale it to publication size with pamscale in order
       to eliminate jagged edges by resampling, it's best to generate the  shadow  in  the  original  high  resolution
       image,  prior  to scaling it down in size.  If you scale first and then add the shadow, you'll get an unsightly
       jagged stripe between the edge of material and its shadow, due to resampled  pixels  intermediate  between  the
       image and background obscuring the shadow.

       ppmshadow  returns  status  0  if  processing was completed without errors, and a nonzero Unix error code if an
       error prevented generation of output.  Some errors may result in the script aborting, usually displaying  error
       messages  from  various  Netpbm components it uses, without returning a nonzero error code.  When this happens,
       the output file will be empty, so be sure to test this if you need to know if the program succeeded.

       pnm(1), pnmmargin(1), pnmconvol(1), pamscale(1), pnmsmooth(1), ppm(1)

       John Walker  August 8, 1997

       This software is in the public domain.  Permission to use, copy, modify, and distribute this software  and  its
       documentation for any purpose and without fee is hereby granted, without any conditions or restrictions.

netpbm documentation             17 April 2005        Ppmshadow User Manual(0)