ppmshadow - add simulated shadows to a portable pixmap image


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


   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 colour of
   the object which casts it.  You can specify the extent  of  the  shadow
   and its displacement from the image with command line options.


   -b blur_size

          Sets  the  distance  of the light source from the image.  Larger
          values move the light source  closer,  casting  a  more  diffuse
          shadow,  while  smaller  settings  move  the light further away,
          yielding a sharper shadow.  blur_size defaults to 11 pixels.

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

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

   -u     Print command syntax and a summary of options.

   -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 an anymap named by the pnmfile command line argument;  if  you
   don't specify pnmfile, the input is the Standard Input file.

   Output is a always a PPM file, written to Standard Output.

   pnmfile creates a number of temporary files as it executes.  It creates
   them in the /tmp directory, with names of the form:


   where pid is the process number of the ppmshadow process  and  N  is  a
   number  identifying  the file as described below.  In normal operation,
   ppmshadow deletes temporary files as soon as it is done with  them  and
   leaves   no   debris  around  after  it  completes.   To  preserve  the
   intermediate files for debugging, use the -k command line option.

   N in the filename means:

   1      Positive binary mask

   2      Convolution kernel for blurring shadow

   3      Blurred shadow image

   4      Clipped shadow image, offset as requested

   5      Blank image with background of source image

   6      Offset shadow

   7      Inverse mask file

   8      Original image times inverse mask

   9      Generated shadow times positive mask

   10     Shadow times background colour


   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 unintentional "holes" in the
   shadow, fill the offending areas with a color which differs from  black
   or  the  background  by RGB values of 1, which will be imperceptible to
   the viewer.  Since the comparison is exact, the modified 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  document for additional
   details and examples of the intermediate files.

   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 colour of the object that casts
   it.   If the contrast 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  1111 kernel, then calls pnmsmooth (which is actually a script that
   calls pnmconvol with a 33 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  pnmscale 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(5), pnmmargin(1), pnmconvol(1), pnmscale(1), pnmsmooth(1), ppm(5)


   John Walker <http://www.fourmilab.ch> 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

                             12 March 2000                    ppmshadow(1)


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