1Pamcomp User Manual(0) Pamcomp User Manual(0)
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6 pamcomp - composite (overlay) two Netpbm images together
7
10 pamcomp
11 [-align={left | center | right | beyondleft | beyondright}]
13 [-valign={top | middle | bottom| above | below}] [-xoff=X] [-yoff=Y]
14 [-alpha=alpha-pgmfile] [-invert] [-opacity=opacity] [-mixtransparency]
15 [-linear] overlay_file [underlying_file [output_file]]
16 Minimum unique abbreviation of option is acceptable. You may use dou‐
18 ble hyphens instead of single hyphen to denote options. You may use
19 white space in place of the equals sign to separate an option name from
20 its value.
21
24 This program is part of Netpbm(1).
25 pamcomp reads two images and produces a composite image with one of the
27 images overlayed on top of the other, possible translucently. The
28 images need not be the same size. The input and outputs are Netpbm
29 format image files.
30 In its simplest use, pamcomp simply places the image in the file over‐
32 lay_file on top of the image in the file underlying_file, blocking out
33 the part of underlying_file beneath it.
34 If you add the -alpha option, then pamcomp uses the image in file
36 alpha-pgmfile as a transparency mask, which means it determines the
37 level of transparency of each point in the overlay image. The trans‐
38 parency mask must have the same dimensions as the overlay image. In
39 places where the transparency mask defines the overlay image to be
40 opaque, the composite output contains only the contents of the overlay
41 image; the underlying image is totally blocked out. In places where
42 the transparency mask defines the overlay image to be transparent, the
43 composite output contains none of the overlay image; the underlying
44 image shows through completely. In places where the transparency mask
45 shows a value in between opaque and transparent (translucence), the
46 composite image contains a mixture of the overlay image and the under‐
47 lying image and the level of translucence determines how much of each.
48 The transparency mask is a PGM file in which a white pixel represents
50 opaqueness and a black pixel transparency. Anything in between is
51 translucent. (Like any Netpbm program, pamcomp will see a PBM file as
52 if it is PGM).
53 If the overlay image is a PAM image of tuple type RGB_ALPHA or
55 GRAYSCALE_ALPHA, then the overlay image contains transparency informa‐
56 tion itself and pamcomp uses it the same way as the transparency mask
57 described above. If you supply both an overlay image that has trans‐
58 parency information and a transparency mask, pamcomp multiplies the two
59 opacities to get the opacity of the overlay pixel.
60 Before Netpbm 10.25 (October 2004), pamcomp did not recognize the
62 transparency information in a PAM image -- it just ignored it. So peo‐
63 ple had to make appropriate transparency masks in order to have a non-
64 opaque overlay. Some Netpbm programs that convert from image formats
65 that contain transparency information are not able to create RGB_ALPHA
66 or GRAYSCALE_ALPHA PAM output, so you have to use the old method --
67 extract the transparency information from the original into a separate
68 transparency mask and use that as input to pamcomp.
69 The output image is always of the same dimensions as the underlying
71 image. pamcomp uses only parts of the overlay image that fit within
72 the underlying image.
73 The output image is a PAM image. Its tuples are color, grayscale, or
75 black and white, whichever is the "highest" format between the two
76 input images. The maxval of the output is the least common multiple of
77 the maxvals of the input, up to the maximum possible PAM maxval, 65535.
78 The output has an opacity channel if and only if the underlying image
80 does, and then the opacities are as described under the -mixtrans‐
81 parency option. Before Netpbm 10.56 (September 2011), the output never
82 has an opacity channel.
83 To specify where on the underlying image to place the overlay image,
85 use the -align, -valign, -xoff, and -yoff options. Without these
86 options, the default horizontal position is flush left and the default
87 vertical position is flush top.
88 The overlay image, in the position you specify, need not fit entirely
90 within the underlying image. pamcomp uses only the parts of the over‐
91 lay image that appear above the underlying image. It is possible to
92 specify positioning such that none of the overlay image is over the
93 underlying image -- i.e. the overlay is out of frame. If you do that,
94 pamcomp issues a warning.
95 The overlay and underlying images may be of different formats (e.g.
97 overlaying a PBM text image over a full color PPM image) and have dif‐
98 ferent maxvals. The output image has the more general of the two input
99 formats and a maxval that is the least common multiple the two maxvals
100 (or the maximum maxval allowable by the format, if the LCM is more than
101 that).
102
106 The overlay_file argument is the name of the file containing the
107 overly image, while underlying_file is the name of the file
108 containing the underlying image. For either, you may specify '-'
109 to indicate Standard Input, and underlying file defaults to Standard
110 Input. Make sure you aren't specifying (or defaulting) Standard
111 Input as
112 both.
113 Note that there may be a third input file, identified by an -alphafile
115 option.
116 The output_file argument is the name of the file to which
118 pamcomp writes the output, creating or truncating it first. You may
119 specify '-' to indicate Standard Output, in which
120 case pamcomp does not truncate it. Note that pamcomp is
121 unusual among Netpbm programs, as a historical accident, in having an
122 output
123 file argument; Netpbm programs normally write to Standard Output
124 only.
125
129 In addition to the options common to all programs based on libnetpbm
130 (most notably -quiet, see
131 Common Options ⟨index.html#commonoptions⟩ ), pamcomp recognizes the
132 following command line options:
133 -align=alignment
137 This option selects the basic horizontal position of the overlay
138 image with respect to the underlying image, in syntax reminis‐
139 cent of HTML. left means flush left, center means centered, and
140 right means flush right.
141 The -xoff option modifies this position.
143 beyondleft means just out of frame to the left -- the right edge
145 of the overlay is flush with the left edge of the underlying
146 image. beyondright means just out of frame to the right. These
147 alignments are useful only if you add a -xoff option. These
148 two values were added in Netpbm 10.10 (October 2002).
149 The default is left.
151 -valign=alignment
154 This option selects the basic vertical position of the overlay
155 image with respect to the underlying image, in syntax reminis‐
156 cent of HTML. top means flush top, middle means centered, and
157 bottom means flush bottom.
158 The -yoff option modifies this position.
160 above means just out of frame to the top -- the bottom edge of
162 the overlay is flush with the top edge of the underlying image.
163 below means just out of frame to the bottom. These alignments
164 are useful only if you add a -yoff option. These two values
165 were added in Netpbm 10.10 (October 2002).
166 The default is top.
168 -xoff=x
171 This option modifies the horizontal positioning of the overlay
172 image with respect to the underlying image as selected by the
173 -align option. pamcomp shifts the overlay image from that basic
174 position x pixels to the right. x can be negative to indicate
175 shifting to the left.
176 The overlay need not fit entirely (or at all) on the underlying
178 image. pamcomp uses only the parts that lie over the underlying
179 image.
180 Before Netpbm 10.10 (October 2002), -xoff was mutually exclusive
182 with -align and always measured from the left edge.
183 -yoff=y
186 This option modifies the vertical positioning of the overlay
187 image with respect to the underlying image as selected by the
188 -valign option. pamcomp shifts the overlay image from that
189 basic position y pixels downward. y can be negative to indicate
190 shifting upward.
191 The overlay need not fit entirely (or at all) on the underlying
193 image. pamcomp uses only the parts that lie over the underlying
194 image.
195 Before Netpbm 10.10 (October 2002), -xoff was mutually exclusive
197 with -valign and always measured from the top edge.
198 -alpha=alpha-pgmfile
201 This option names a file that contains the transparency mask.
202 If you don't specify this option, there is no transparency mask,
203 which is equivalent to having a transparency mask specify total
204 opaqueness everywhere.
205 You can specify - as the value of this option and the trans‐
207 parency mask will come from Standard Input. If you do this,
208 don't specify Standard Input as the source of any other input
209 image.
210 -invert
213 This option inverts the sense of the values in the transparency
214 mask, which effectively switches the roles of the overlay image
215 and the underlying image in places where the two intersect.
216 -opacity=opacity
219 This option tells how opaque the overlay image is to be, i.e.
220 how much of the composite image should be from the overlay
221 image, as opposed to the underlying image. opacity is a float‐
222 ing point number, with 1.0 meaning the overlay image is totally
223 opaque and 0.0 meaning it is totally transparent. The default
224 is 1.0.
225 If you specify a transparency mask (the -alpha option), pamcomp
227 uses the product of the opacity indicated by the transparency
228 mask (as modified by the -invert option, as a fraction, and this
229 opacity value. The -invert option does not apply to this opac‐
230 ity value.
231 As a simple opacity value, the value makes sense only if it is
233 between 0 and 1, inclusive. However, pamcomp accepts all values
234 and performs the same arithmetic computation using whatever
235 value you provide. An opacity value less than zero means the
236 underlay image is intensified and then the overlay image is
237 "subtracted" from it. An opacity value greater than unity means
238 the overlay image is intensified and the underlay image sub‐
239 tracted from it. In either case, pamcomp clips the resulting
240 color component intensities so they are nonnegative and don't
241 exceed the output image's maxval.
242 This may seem like a strange thing to do, but it has uses. You
244 can use it to brighten or darken or saturate or desaturate areas
245 of the underlay image. See this description(1) of the tech‐
246 nique.
247 This option was added in Netpbm 10.6 (July 2002). Before Netpbm
249 10.15 (April 2003), values less than zero or greater than unity
250 were not allowed.
251 -mixtransparency
254 This option controls what pamcomp does where both the underlying
255 and overlay image are non-opaque.
256 By default, the output image has the same transparency as the
258 underlying image and the transparency of the underlying image
259 has no effect on the composition of color.
260 But with this option, pamcomp composes the image according to a
262 plastic transparency metaphor: the underlying and overlay images
263 are plastic slides. The output image is the slide you get when
264 you stack up those two slides. So the transparency of the out‐
265 put is a combination of the transparency of the inputs and the
266 transparency of the underlying image affects the underlying
267 image's contribution to the output image's color.
268 Unlike the metaphorical slide, a PAM pixel has a color even
270 where it is completely transparent, so pamcomp departs from the
271 metaphor in that case and makes the output color identical to
272 the underlying image.
273 This option was new in Netpbm 10.56 (September 2011). Before
275 that, the output is always opaque and the pamcomp ignores the
276 transparency of the underlying image.
277 -linear
280 This option indicates that the inputs are not true Netpbm images
281 but rather a light-intesity-proportional variation. This is
282 relevant only when you mix pixels, using the -opacity option or
283 a transparency mask (the -alpha option).
284 The transparency mask and -opacity values indicate a fraction of
286 the light intensity of a pixel. But the PNM and PNM-equivalent
287 PAM image formats represent intensities with gamma-adjusted num‐
288 bers that are not linearly proportional to intensity. So pam‐
289 comp, by default, performs a calculation on each sample read
290 from its input and each sample written to its output to convert
291 between these gamma-adjusted numbers and internal intensity-pro‐
292 portional numbers.
293 Sometimes you are not working with true PNM or PAM images, but
295 rather a variation in which the sample values are in fact
296 directly proportional to intensity. If so, use the -linear
297 option to tell pamcomp this. pamcomp then will skip the conver‐
298 sions.
299 The conversion takes time. And the difference between inten‐
301 sity-proportional values and gamma-adjusted values may be small
302 enough that you would barely see a difference in the result if
303 you just pretended that the gamma-adjusted values were in fact
304 intensity-proportional. So just to save time, at the expense of
305 some image quality, you can specify -linear even when you have
306 true PPM input and expect true PPM output.
307 For the first 13 years of Netpbm's life, until Netpbm 10.20
309 (January 2004), pamcomp's predecessor pnmcomp always treated the
310 PPM samples as intensity-proportional even though they were not,
311 and drew few complaints. So using -linear as a lie is a reason‐
312 able thing to do if speed is important to you.
313 Another technique to consider is to convert your PNM image to
315 the linear variation with pnmgamma, run pamcomp on it and other
316 transformations that like linear PNM, and then convert it back
317 to true PNM with pnmgamma -ungamma. pnmgamma is often faster
318 than pamcomp in doing the conversion.
319
325 pammixmulti.html(1) mixes together two or more images of the same size,
326 in various ways.
327 ppmmix(1) and pnmpaste(1) are simpler, less general versions of the
329 same tool.
330 ppmcolormask(1) and pbmmask(1), and pambackground(1) can help with gen‐
332 erating a transparency mask.
333 pnmcomp(1) is an older program that runs faster, but has less function.
335 pnm(1)
337
341 pamcomp was new in Netpbm 10.21 (March 2004). Its predecessor, pnm‐
342 comp, was one of the first programs added to Netpbm when the project
343 went global in 1993.
344
348 Copyright (C) 1992 by David Koblas (koblas@mips.com).
349
351 This manual page was generated by the Netpbm tool 'makeman' from HTML
352 source. The master documentation is at
353 http://netpbm.sourceforge.net/doc/pamcomp.html
355netpbm documentation 13 August 2011 Pamcomp User Manual(0)