1Pnmcrop User Manual(0) Pnmcrop User Manual(0)
2
6 pnmcrop - crop a Netpbm image
7
10 pnmcrop
11 [-white |-black |-sides |-bg-color=color |-bg-corner={
13 topleft|topright|bottomleft|bottomright} ]
14 [-left]
16 [-right]
18 [-top]
20 [-bottom]
22 [-margin=pixels]
24 [-closeness=closeness_percent]
26 [-borderfile=filename]
28 [-blank-image={abort|pass|minimize|maxcrop}]
30 {[-reportfull]|[-reportsize]}
32 [-verbose]
34 [pnmfile]
36 Minimum unique abbreviation of option is acceptable. You may use dou‐
38 ble hyphens instead of single hyphen to denote options. You may use
39 white space in place of the equals sign to separate an option name from
40 its value.
41
44 This program is part of Netpbm(1).
45 pnmcrop reads a PBM, PGM, or PPM image as input, removes borders that
47 are the background color, and produces the same type of image as out‐
48 put.
49 If you don't specify otherwise, pnmcrop assumes the background color is
51 whatever color the top left and right corners of the image are and if
52 they are different colors, something midway between them. You can
53 specify that the background is white or black with the -white and
54 -black options or make pnmcrop base its guess on all four corners in‐
55 stead of just two with -sides.
56 By default, pnmcrop chops off any stripe of background color it finds,
58 on all four sides. You can tell pnmcrop to remove only specific bor‐
59 ders with the -left, -right,
60 -top, and -bottom options.
61 But note that pnmcrop's determination of the background color is inde‐
63 pendent of which edges you crop, which may not be intuitive. For exam‐
64 ple, imagine an image with a blue border at the top and a black border
65 at the bottom and you say to crop the bottom (-bottom). You may have
66 expected to crop the black border, but you actually won't crop any‐
67 thing, because pnmcrop considers the background color to be whatever
68 color the top two corners are, which is blue, and there is no blue at
69 the bottom of the image. If you do want pnmcrop to take the background
70 color from the edges being cropped, use -bg-corner.
71 If you want to leave some border, use the -margin option. It will not
74 only spare some of the border from cropping, but will fill in (with
75 what pnmcrop considers the background color) if necessary to get up to
76 that size.
77 If the input is a multi-image stream, pnmcrop processes each one inde‐
79 pendently and produces a multi-image stream as output. It chooses
80 where to crop independently for each image. So if you start with a
81 stream of images of the same dimensions, you may end up with images of
82 differing dimensions. Before Netpbm 10.37 (December 2006), pnmcrop ig‐
83 nored all input images but the first.
84 If you want to chop a specific amount off the side of an image, use
86 pamcut.
87 If you want to add different borders after removing the existing ones,
89 use pnmcat or pamcomp.
90
94 In addition to the options common to all programs based on libnetpbm
95 (most notably -quiet, see
96 Common Options ⟨index.html#commonoptions⟩ ), pnmcrop recognizes the
97 following command line options:
98 -white Take white to be the background color. pnmcrop removes borders
102 which are white.
103 You may specify at most one of -black, -white, -sides, -bg-
105 color, and -bg-corner.
106 -black Take black to be the background color. pnmcrop removes borders
109 which are black.
110 You may specify at most one of -black, -white, -sides, -bg-
112 color, and -bg-corner.
113 -bg-color=color
116 This tells pnmcrop what color is the background - it will crop
117 areas of this color. color is a value that would be used as the
118 argument of the pnm_parsecolor() library routine
119 ⟨libnetpbm_image.html#colorname⟩ .
120 You may specify at most one of -black, -white, -sides, -bg-
122 color, and -bg-corner.
123 This option was new in Netpbm 10.86 (March 2019).
125 -sides Determine the background color from the colors of the four cor‐
128 ners of the input image. pnmcrop removes borders which are of
129 the background color.
130 If at least three of the four corners are the same color, pnm‐
132 crop takes that as the background color. If not, pnmcrop looks
133 for two corners of the same color in the following order, taking
134 the first found as the background color: top, left, right, bot‐
135 tom. If all four corners are different colors, pnmcrop assumes
136 an average of the four colors as the background color.
137 The -sides option slows pnmcrop down, as it reads the entire im‐
139 age to determine the background color in addition to the up to
140 three times that it would read it without -sides.
141 You may specify at most one of -black, -white, -sides, -bg-
143 color, and -bg-corner.
144 -bg-corner={topleft|topright|bottomleft|bottomright
147 This option indicates a corner which is background. pnmcrop
148 will use the color of this corner as the background color and
149 crop edges of that color.
150 You may specify at most one of -black, -white, -sides, -bg-
152 color, and -bg-corner.
153 This option was new in Netpbm 10.86 (March 2019).
155 -left Remove any left border.
158 -right Remove any right border.
161 -top Remove any top border.
164 -bottom
167 Remove any bottom border.
168 -margin=pixels
171 Leave pixels pixels of border. Expand the border to this size
172 if necessary.
173 This option was new in Netpbm 10.29 (August 2005).
175 -closeness=closeness_percent
178 Any color in the image that is at least this close to the opera‐
179 tive background color is considered to be background.
180 You can use this if the image has borders that vary slightly in
182 color, such as would be the case in a photograph. Consider a
183 photograph against a white screen. The color of the screen
184 varies slightly with shading and dirt and such, but is still
185 quite distinct in color from the subject of the photograph. pn‐
186 mcrop will choose some particular shade as the background color
187 and if you specify an appropriate -closeness value, it will cor‐
188 rectly identify all of the screen as background and crop it off.
189 To implement more complex rules for identifying background, use
191 -borderfile.
192 The default is zero, which means a pixel's color must exactly
194 match the background color for the pixel to be considered part
195 of a background border.
196 This option was new in Netpbm 10.78 (March 2017). With older
198 Netpbm, colors must match exactly.
199 -borderfile=filename
202 Use the image in the file named filename instead of the input
203 image to determine where the borders of the input image are and
204 the background color.
205 Without this option, pnmcrop examines the input image and fig‐
207 ures out what part of the image is border and what part is fore‐
208 ground (not border), as well as the background color. With this
209 option, pnmcrop finds the borders in one image, then uses the
210 those four border sizes (left, right, top, bottom) in cropping a
211 different image. Furthermore, if you use -margin to add bor‐
212 ders, the color of those borders is the background color pnmcrop
213 detects in the border file.
214 The point of this is that you may want to help pnmcrop to come
216 to a different conclusion as to where the borders are and what
217 the background color is by preprocessing the input image. For
218 example, consider an image that has speckles of noise in its
219 borders. pnmcrop isn't smart enough to recognize these as
220 noise; it sees them as foreground image. So pnmcrop considers
221 most of your borders to be foreground and does not crop them off
222 as you want. To fix this, run the image through a despeckler
223 such as pbmclean and tell pnmcrop to use the despeckled version
224 of the image as the -borderfile image, but the original speckled
225 version as the input image. That way, you crop the borders, but
226 retain the true foreground image, speckles and all.
227 The border file must have the same number of images in it as the
229 input file; the background color determination for image N of
230 the input is based on the image N of the border file.
231 This option was new in Netpbm 10.29 (August 2005).
233 Before Netpbm 10.46 (March 2009), the original image and not the
235 border file determines the background color. pnmcrop fails if
236 there is no apparent background color in the original image
237 (i.e. the corners of the image don't have a common color).
238 -blank-image={abort|pass|minimize|maxcrop}
241 This determines how pnmcrop handles an image which is entirely
242 background (blank), a case where cropping doesn't make much
243 sense.
244 abort
248 program fails, with explanatory message (default)
250 pass
253 Output image is the same as the input image.
255 -margin has no effect.
256 minimize
259 output is a single row, column, or pixel (of the background
261 color).
262 If you crop both vertically and horizontally (the de‐
263 fault), it is a
264 single pixel. If you crop only vertically, a single row,
265 of the
266 original width. If you crop only horizontally, it is a
267 single column,
268 of the original height.
269 This is a somewhat incongruous result; the mathematically con‐
271 sistent
272 result of cropping the background from an image that is
273 entirely
274 background would be an image with no pixels at all. But
275 such a thing
276 does not exist in the Netpbm formats (and you probably
277 wouldn't want
278 it anyway, because whoever processes this output may not
279 tolerate
280 that).
281 The background can be more than one color when you specify
283 -closeness, so it matters which row, column, or pixel re‐
284 mains.
285 If you crop on the top and not bottom, it is the last row
286 that remains.
287 If you crop on both the top and bottom, it is the middle
288 row that
289 remains. The other cases follow similarly.
290 If you specify a margin (-margin), the output image consists
292 entirely of the margins; there is no single row, column,
293 or pixel
294 between the margins. So with -margin, the incongruity
295 mentioned above does not exist. But before Netpbm 10.92
296 (September
297 2020), -margin was ignored with -blank-image=minimize.
298 maxcrop
301 This odd function selects a hypothetical cropping which is not
303 even
304 possible, and therefore is valid only with -reportfull or
305 -reportsize. The cropping that this selects is a crop of
306 the
307 entire image on every side on which you request cropping.
308 So if you
309 request cropping only on the left, of a 600 pixel wide im‐
310 age, this
311 selects a cropping of 600 pixels from the left and none
312 from the other
313 three sides. Note that were this cropping actually ap‐
314 plied, this would
315 produce an image with no pixels, which is not a valid
316 Netpbm image. But
317 it gets stranger still if you request cropping on both the
318 right and the
319 left. In that case, the cropping selected is a cropping
320 of 600 pixels
321 from both the right and left sides, which would leave a
322 negative-width
323 image.
324 This is actually useful if you are trying to find a single
326 set of
327 cropping parameters to crop a stream of images. To do
328 this, you could
329 do a pass with -reportsize and -blank-image=maxcrop to
330 compute the maximum crop for each edge, and then use those
331 numbers in
332 -cropxxx options on a pamcut pass to do the crop.
333 In this scenario, any all-background (blank) images would
334 have no effect
335 on the cropping parameters you compute. If you do this,
336 you must give
337 special consideration to a stream with nothing but blank
338 images.
339 -margin is always ignored when the image is all background.
343 This option was new in Netpbm 10.86 (March 2019).
345 -reportfull
348 With this option, pnmcrop does not actually crop anything. In‐
349 stead, it just prints to Standard Output parameters of the crop‐
350 ping it would have done. The output is a single line per image,
351 like in this example:
352 0 +7 -20 -10 200 300 rgb-255:10/0/255 0.0
355 The line is composed of the following blank-delimited tokens:
359 • how many pixels would be cropped or padded on the left. This is
363 a signed decimal number, where + means pad and - means crop.
364 If there
365 would be no change, this is unsigned zero.
366 • same, but for the right side.
369 • same, but for the top.
372 • same, but for the bottom.
375 • the resulting image width in pixels, in decimal.
378 • the resulting image height in pixels, in decimal.
381 • The color pnmcrop took to be the background color, like
384 'rgb-255:10/0/255' (This is a format recognized by
385 the pnm_parsecolor() ⟨libnetpbm_image.html#colorname⟩
386 library routine). The maxval in the color specification is
387 the maxval of
388 the image.
389 • The closeness value (see -closeness option) pnmcrop
392 used, in floating point decimal.
393 You cannot use -borderfile together with this option.
396 This option was new in Netpbm 10.86 (March 2019).
398 -reportsize
401 This is like -reportfull, but reports only the left, right, top,
402 bottom, width, and height.
403 You cannot use -borderfile together with this option.
405 This option was new in Netpbm 10.86 (March 2019).
407 -verbose
410 Print on Standard Error information about the processing, in‐
411 cluding exactly how much is being cropped off of which sides.
412
417 pamcut(1), pamfile(1), pnm(1)
418
421 Copyright (C) 1989 by Jef Poskanzer.
422
424 This manual page was generated by the Netpbm tool 'makeman' from HTML
425 source. The master documentation is at
426 http://netpbm.sourceforge.net/doc/pnmcrop.html
428netpbm documentation 16 August 2020 Pnmcrop User Manual(0)