1Ppmshadow User Manual(0) Ppmshadow User Manual(0)
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6 ppmshadow - add simulated shadows to a PPM image
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10 ppmshadow [-b blur_size] [-k] [-t] [-x xoffset] [-y yoffset] [ppmfile]
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15 This program is part of Netpbm(1).
16 ppmshadow adds a simulated shadow to an image, giving the appearance
18 that the contents of the image float above the page, casting a diffuse
19 shadow on the background. Shadows can either be black, as cast by
20 opaque objects, or translucent, where the shadow takes on the color of
21 the object which casts it. You can specify the crispness of the shadow
22 and its displacement from the image with command line options.
23 ppmshadow sees your image as a foreground on a background. The back‐
25 ground color is whatever color the top left pixel of your image is.
26 The background is all the pixels that are that color and the foreground
27 is everything else. The shadow that ppmshadow generates is a shadow of
28 the foreground, cast on the background.
29 The shadow is the same size as the foreground, plus some fringes as
31 determined by the -b option. It is truncated to fit in your image.
32 The output image is the same dimensions as the input image.
33 You can use pamcomp to place a foreground image over a background
35 before running ppmshadow on it. You can use ppmmake to make the back‐
36 ground image (just an image of a solid color).
37 The output has the same dimensions and maxval as the input.
39 The blurring to make the fringes of the shadow will not have a desir‐
41 able effect if the color depth (maxval) of the image is too low -- you
42 need a high maxval to get all the shades needed to create a smooth gra‐
43 dient. So if your input has low maxval (including most notably if the
44 input is PBM, which means its maxval is 1), run it through pamdepth to
45 raise its maxval. 255 is usually a good choice.
46 Input is a PPM file named by the ppmfile command line argument; if you
48 don't specify ppmfile, the input is Standard Input.
49 The output is a PPM file, written to Standard Output.
51
55 -b blur_size
56 Sets the distance of the light source from the image. Larger
57 values move the light source closer, casting a more diffuse
58 shadow, while smaller settings move the light further away,
59 yielding a sharper shadow. blur_size is the number of pixels of
60 fringe there is on the shadow, beyond where the shadow would be
61 if there were no blurring.
62 The default is 11 pixels.
64 Note that this option controls only the fringing effect of mov‐
66 ing the light source closer to the object. It does not make the
67 shadow grow or shrink as would happpen in the real world if you
68 moved a point light source closer to and further from an object.
69 -k Keep the intermediate temporary image files. When debugging,
72 these intermediate files provide many clues as to the source of
73 an error. See below ⟨#files⟩ for a list of the contents of
74 each file.
75 -t Consider the non-background material in the image translucent --
78 it casts shadows of its own color rather than a black shadow,
79 which is default. This often results in fuzzy, difficult-to-
80 read images but in some circumstances may look better.
81 -x xoffset
84 Specifies the displacement of the light source to the left of
85 the image. Larger settings of xoffset displace the shadow to
86 the right, as would be cast by a light further to the left. If
87 not specified, the horizontal offset is half of blur_size
88 (above), to the left.
89 -y yoffset
92 Specifies the displacement of the light source above the top of
93 the image. Larger settings displace the shadow downward, corre‐
94 sponding to moving the light further above the top of the image.
95 If you don't specify -y, the vertical offset defaults to the
96 same as the horizontal offset (above), upward.
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103 The source image must contain sufficient space on the edges in the
104 direction in which the shadow is cast to contain the shadow -- if it
105 doesn't some of the internal steps may fail. You can usually expand
106 the border of a too-tightly-cropped image with pnmmargin before pro‐
107 cessing it with ppmshadow.
108 Black pixels and pixels with the same color as the image background
110 don't cast a shadow. If this causes unintentional "holes" in the
111 shadow, fill the offending areas with a color which differs from black
112 or the background by RGB values of 1, which will be imperceptible to
113 the viewer. Since the comparison is exact, the modified areas will now
114 cast shadows.
115 The background color of the source image (which is preserved in the
117 output) is deemed to be the color of the pixel at the top left of the
118 input image. If that pixel isn't part of the background, simply add a
119 one-pixel border at the top of the image, generate the shadow image,
120 then delete the border from it.
121 If something goes wrong along the way, the error messages from the var‐
123 ious Netpbm programs ppmshadow calls will, in general, provide little
124 or no clue as to where ppmshadow went astray. In this case, Specify
125 the -k option and examine the intermediate results in the temporary
126 files (which this option causes to be preserved). If you manually run
127 the commands that ppmshadow runs on these files, you can figure out
128 where the problem is. In problem cases where you want to manually
129 tweak the image generation process along the way, you can keep the
130 intermediate files with the -k option, modify them appropriately with
131 an image editor, then recombine them with the steps used by the code in
132 ppmshadow.
133 Shadows are by default black, as cast by opaque material in the image
135 occluding white light. Use the -t option to simulate translucent mate‐
136 rial, where the shadow takes on the color of the object that casts it.
137 If the contrast between the image and background is insufficient, the
138 -t option may yield unattractive results which resemble simple blurring
139 of the original image.
140 Because Netpbm used to have a maximum maxval of 255, which meant that
142 the largest convolution kernel pnmconvol could use was 11 by 11,
143 ppmshadow includes a horrid, CPU-time-burning kludge which, if a blur
144 of greater than 11 is requested, performs an initial convolution with
145 an 11 x 11 kernel, then calls pnmsmooth (which is itself a program that
146 calls pnmconvol with a 3 x 3 kernel) as many times as the requested
147 blur exceeds 11. It's ugly, but it gets the job done on those rare
148 occasions where you need a blur greater than 11.
149 If you wish to generate an image at high resolution, then scale it to
151 publication size with pamscale in order to eliminate jagged edges by
152 resampling, it's best to generate the shadow in the original high reso‐
153 lution image, prior to scaling it down in size. If you scale first and
154 then add the shadow, you'll get an unsightly jagged stripe between the
155 edge of material and its shadow, due to resampled pixels intermediate
156 between the image and background obscuring the shadow.
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160 ppmshadow returns status 0 if processing was completed without errors,
161 and a nonzero Unix error code if an error prevented generation of out‐
162 put. Some errors may result in the script aborting, usually displaying
163 error messages from various Netpbm components it uses, without return‐
164 ing a nonzero error code. When this happens, the output file will be
165 empty, so be sure to test this if you need to know if the program suc‐
166 ceeded.
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170 pnm(1), pnmmargin(1), pnmconvol(1), pamscale(1), pnmsmooth(1), ppm(1)
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175 ppmshadow creates a number of temporary files as it executes. It cre‐
176 ates a new directory for them in the directory named by the TMPDIR
177 environment variable, defaulting to /tmp if it is not set.
178 In normal operation, ppmshadow finds a unique name for the temporary
180 directory and deletes each temporary file as soon as it is done with it
181 and leaves no debris around after it completes. To preserve the inter‐
182 mediate files for debugging, use the -k command line option. In that
183 case, the directory name is ppmshadowpid, where pid is the process ID
184 of the ppmshadow process, and the program fails if ppmshadow cannot
185 create that directory because the name is already in use.
186 The temporary files are:
188 infile.ppm
192 A copy of the input.
193 background.ppm
196 Blank image with background of source image
197 bgmask.ppm
200 Positive binary mask
201 convkernel.ppm
204 Convolution kernel for blurring shadow
205 blurredlackshad.ppm
208 Blurred shadow image before coloring
209 blurred.ppm
212 Blurred, colored shadow image
213 shadow.ppm
216 Clipped shadow image, offset as requested
217 shadback.ppm
220 Generated shadow times positive mask
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226 John Walker http://www.fourmilab.ch ⟨http://www.fourmilab.ch⟩ August
227 8, 1997
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231 This software is in the public domain. Permission to use, copy, mod‐
232 ify, and distribute this software and its documentation for any purpose
233 and without fee is hereby granted, without any conditions or restric‐
234 tions.
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237 This manual page was generated by the Netpbm tool 'makeman' from HTML
238 source. The master documentation is at
239 http://netpbm.sourceforge.net/doc/ppmshadow.html
241netpbm documentation 24 June 2017 Ppmshadow User Manual(0)