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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 crispness 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 what-
       ever 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 truncated 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, casting 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

	      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

       -k     Keep the intermediate temporary image files.  When  debugging,  these  intermediate
	      files  provide  many clues as to the source of an error.	See below <#files>  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  ppm-
       file, 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 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 com-
       mands 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 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 convolu-
       tion  kernel pnmconvol could use was 11 by 11, ppmshadow includes a horrid, CPU-time-burn-
       ing kludge which, if a blur of greater than 11 is requested, performs an initial  convolu-
       tion  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 http://www.fourmilab.ch <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 restrictions.

netpbm documentation			  17 April 2005 		 Ppmshadow User Manual(0)
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