1Pamarith User Manual(0) Pamarith User Manual(0)
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6 pamarith - perform arithmetic on two Netpbm images
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10 pamarith -add | -subtract | -multiply | -divide | -difference | -mini‐
11 mum | -maximum | -mean | -compare | -and | -or | -nand | -nor | -xor |
12 -shiftleft | -shiftright pamfile1 pamfile2
13 All options can be abbreviated to their shortest unique prefix. You
15 may use two hyphens instead of one. You may separate an option name
16 and its value with white space instead of an equals sign.
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20 This program is part of Netpbm(1).
21 pamarith reads two PBM, PGM, PPM, or PAM images as input. It performs
23 the specified binary arithmetic operation on their sample values and
24 produces an output of a format which is the more general of the two
25 input formats. The two input images must be of the same width and
26 height. The arithmetic is performed on each pair of identically
27 located tuples to generate the identically located tuple of the output.
28 For the purpose of the calculation, it assumes any PBM, PGM, or PPM
30 input image is the equivalent PAM image of tuple type BLACKANDWHITE,
31 GRAYSCALE, or RGB, respectively, and if it produces a PBM, PGM, or PPM
32 output, produces the equivalent of the PAM image which is the result of
33 the calculation.
34 The first pamfile argument identifies the "left" argument image; the
36 second pamfile argument identifies the "right" one.
37 If the output is PAM, the tuple type is the same as the tuple type of
39 the left input image.
40 pamarith performs the arithmetic on each pair of identically located
42 tuples in the two input images.
43 The arithmetic operation is in all cases fundamentally a function from
45 two integers to an integer (but see below - the functions are defined
46 in ways that you can effectively e.g. add real numbers). The operation
47 is performed on two tuples as follows. The two input images must have
48 the same depth, or one of them must have depth one. pamarith fails if
49 one of these is not the case.
50 If they have the same depth, pamarith simply carries out the arithmetic
52 one sample at a time. I.e. if at a particular position the left input
53 image contains the tuple (s1,s2,...,sN) and the right input image con‐
54 tains the tuple (t1,t2,...tN), and the function is f, then the output
55 image contains the tuple (f(s1,t1),f(s2,t2),...,f(sN,tN)).
56 If one of the images has depth 1, the arithmetic is performed between
58 the one sample in that image and each of the samples in the other.
59 I.e. if at a particular position the left input image contains the
60 tuple (s) and the right input image contains the tuple (t1,t2,...tN),
61 and the function is f, then the output image contains the tuple
62 (f(s,t1),f(s,t2),...,f(s,tN)).
63 Maxval
66 The meanings of the samples with respect to the maxval varies according
67 to the function you select.
68 In PAM images in general, the most usual meaning of a sample (the one
70 that applies when a PAM image represents a visual image), is that it
71 represents a fraction of some maximum. The maxval of the image corre‐
72 sponds to some maximum value (in the case of a visual image, it corre‐
73 sponds to "full intensity."), and a sample value divided by the maxval
74 gives the fraction.
75 For pamarith, this interpretation applies to the regular arithmetic
77 functions: -add, -subtract, -multiply, -divide, -difference, -minimum,
78 -maximum, -mean, and -compare. For those, you should think of the
79 arguments and result as numbers in the range [0,1). For example, if
80 the maxval of the left argument image is 100 and the maxval of the
81 right argument image is 200 and the maxval of the output image is 200,
82 and the left sample value in an -add calculation is 50 and the right
83 sample is 60, the actual calculation is 50/100 + 60/200 = 160/200, and
84 the output sample value is 160.
85 For these functions, pamarith makes the output image's maxval the maxi‐
87 mum of the two input maxvals, except with -compare, where pamarith uses
88 an output maxval of 2. (Before Netpbm 10.14 (February 2003), there was
89 no exception for -compare; in 10.14, the exception was just that the
90 maxval was at least 2, and sometime between 10.18 and 10.26 (January
91 2005), it changed to being exactly 2).
92 If the result of a calculation falls outside the range [0, 1), pamarith
94 clips it -- i.e. considers it to be zero or 1-.
95 In many cases, where both your input maxvals are the same, you can just
97 think of the operation as taking place between the sample values
98 directly, with no consideration of the maxval except for the clipping.
99 E.g. an -add of sample value 5 to sample value 8 yields sample value
100 13.
101 But with -multiply, this doesn't work. Say your two input images have
103 maxval 255, which means the output image also has maxval 255. Consider
104 a location in the image where the input sample values are 5 and 10.
105 You might think the multiplicative product of those would yield 50 in
106 the output. But pamarith carries out the arithmetic on the fractions
107 5/255 and 10/255. It multiplies those together and then rescales to
108 the output maxval, giving a sample value in the output PAM of 50/255
109 rounded to the nearest integer: 0.
110 With the bit string operations, the maxval has a whole different mean‐
112 ing. The operations in question are: -and, -or, -nand, -nor, -xor, and
113 -shiftleft, -shiftright.
114 With these, each sample value in one or both input images, and in the
116 output image, represents a bit string, not a number. The maxval tells
117 how wide the bit string is. The maxval must be a full binary count (a
118 power of two minus one, such as 0xff) and the number of ones in it is
119 the width of the bit string. For the dyadic bit string operations
120 (that's everything but the shift functions), the maxvals of the input
121 images must be the same and pamarith makes the maxval of the output
122 image the same.
123 For the bit shift operations, the output maxval is the same as the left
125 input maxval. The right input image (which contains the shift counts)
126 can have any maxval and the maxval is irrelevant to the interpretation
127 of the samples. The sample value is the actual shift count. But it's
128 still required that no sample value exceed the maxval.
129 The Operations
132 Most of the operations are obvious from the option name. The following
133 paragraphs cover those that aren't.
134 -subtract subtracts a value in the right input image from a value in
136 the left input image.
137 -difference calculates the absolute value of the difference.
139 -multiply does an ordinary arithmetic multiplication, but tends to pro‐
141 duce nonobvious results because of the way pamarith interprets sample
142 values. See Maxval ⟨#maxval⟩ .
143 -divide divides a value in the left input image by the value in the
145 right input image. But like -multiply, it tends to produce nonobvious
146 results. Note that pamarith clipping behavior makes this of little use
147 when the left argument (dividend) is greater than the right argument
148 (divisor) -- the result in that case is always the maxval. If the
149 divisor is 0, the result is the maxval. This option was new in Netpbm
150 10.30 (October 2005).
151 -compare produces the value 0 when the value in the left input image is
153 less than the value in the right input image, 1 when the values are
154 equal, and 2 when the left is greater than the right.
155 If the maxvals of the input images are not identical, pamarith may
157 claim two values are not equal when in fact they are, because of the
158 precision with which it does the arithmetic. However, it will never
159 say A is greater than B if A is less than B.
160 -compare was new in Netpbm 10.13 (December 2002).
162 -and, -nand, -or, -nor, and -xor consider the input and output images
164 to contain bit strings; they compute bitwise logic operations. Note
165 that if the maxval is 1, you can also look at these as logic operations
166 on boolean input values. See section Maxval ⟨#maxval⟩ for the special
167 meaning of maxval with respect to bit string operations such as these.
168 -shiftleft and -shiftright consider the left input image and output
170 image to contain bit strings. They compute a bit shift operation, with
171 bits falling off the left or right end and zeroes shifting in, as
172 opposed to bits off one end to the other. The right input image sample
173 value is the number of bit positions to shift.
174 Note that the maxval (see Maxval ⟨#maxval⟩ ) determines the width of
176 the frame within which you are shifting.
177 Notes
180 If you want to apply a unary function, e.g. "halve", to a single image,
181 use pamfunc.
182
185 pamfunc(1), pamsummcol(1), pamsumm(1), pnminvert(1), ppmbrighten(1),
186 ppmdim(1), pnmconvol(1), pamdepth(1), pnmpsnr(1), pnm(1), pam(1)
187
191 pamarith replaced pnmarith in Netpbm 10.3 (June 2002).
192 In Netpbm 10.3 through 10.8, though, pamarith was not backward compati‐
194 ble because it required the input images to be of the same depth, so
195 you could not multiply a PBM by a PPM as is often done for masking.
196 (It was not intended at the time that pnmarith would be removed from
197 Netpbm -- the plan was just to rewrite it to use pamarith; it was
198 removed by mistake).
199 But starting with Netpbm 10.9 (September 2002), pamarith allows the
201 images to have different depths as long as one of them has depth 1, and
202 that made it backward compatible with pnmarith.
203 The original pnmarith did not have the -mean option.
205 The -compare option was added in Netpbm 10.13 (December 2002).
207 The bit string operations were added in Netpbm 10.27 (March 2005).
209 The -divide option was added in Netpbm 10.30 (October 2005).
211
213 This manual page was generated by the Netpbm tool 'makeman' from HTML
214 source. The master documentation is at
215 http://netpbm.sourceforge.net/doc/pamarith.html
217netpbm documentation 03 January 2015 Pamarith User Manual(0)