1Ppmhist User Manual(0) Ppmhist User Manual(0)
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6 ppmhist - print a histogram of the colors in a PPM image
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10 ppmhist [-hexcolor | -float | -colorname | -map] [-nomap] [-noheader]
11 [-sort={frequency,rgb}] [-forensic] [ppmfile]
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15 This program is part of Netpbm(1).
16 ppmhist reads a PPM image as input and generates a histogram of the
18 colors in the image, i.e. a list of all the colors and how many pixels
19 of each color are in the image.
20 Output Format
23 The output is in one of two basic formats: a report for humans and a
24 PPM image for use by programs. The PPM image is actually quite read‐
25 able by humans too.
26 Human Report
28 You get this format by specifying (or defaulting to) the -nomap option.
30 The format is one line for each color in the input image.
32 By default, there are two lines of column header and a summary at the
34 top. Use the -noheader option to suppress those lines.
35 The summary tells you whether black or white are present and how many
37 shades of gray and color are present. The summary was new in Netpbm
38 10.82 (March 2018).
39 In each line, ppmhist identifies the color by red, green, and blue com‐
42 ponents. By default, it lists each of these in decimal, using the
43 exact values that are in the PPM input. So if the image has a maxval
44 of 255, the numbers in the listing range from 0 to 255. With the -hex‐
45 color option, you can change these numbers to hexadecimal. With the
46 -float option, the numbers are fractional, adjusted to a maxval of 1.
47 Each line lists the luminosity of the color. It is in decimal on the
49 same scale as the rgb values (see above).
50 Each line lists the number of pixels in the image that have the color.
52 This is in decimal.
53 PPM Output
56 You get this format with the -map option.
58 The output file is a genuine PPM image, but it is PPM Plain format and
60 contains comments so that it is not a lot different from the human
61 report described above.
62 As a PPM image, it can be useful as input to other programs that need
64 some kind of palette. The image is a single row with one column for
65 each distinct color in the image.
66 The function of PPM output is essentially the same as the output of
68 pnmcolormap all. ppmhist is much older than pnmcolormap.
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73 In addition to the options common to all programs based on libnetpbm
74 (most notably -quiet, see
75 Common Options ⟨index.html#commonoptions⟩ ), ppmhist recognizes the
76 following command line options:
77 -sort={frequency,rgb}
82 The -sort option determines the order in which the colors are
83 listed in the output. rgb means to sort them first by the
84 intensity of the red component of the color, then of the green,
85 then of the blue, with the least intense first. frequency means
86 to list them in order of how many pixels in the input image have
87 the color, with the most represented colors first. Among colors
88 with the same frequency, the order is the same as with rgb.
89 The default is frequency.
91 Before Netpbm 10.88 (September 2019), with -sort=frequency, the
93 order of colors that have the same frequency is arbitrary.
94 -hexcolor
97 Print the color components in hexadecimal. See output format
98 ⟨#output⟩ .
99 You may not specify this option along with -float or map.
101 -float Print the color components and the luminosity as floating point
104 numbers in the range [0,1]. See output format ⟨#output⟩ .
105 You may not specify this option along with -hexcolor or map.
107 This option was added in Netpbm 10.19 (November 2003).
109 -map Generates a PPM file of the colormap for the image, with the
112 color histogram as comments. See output format ⟨#output⟩ .
113 You may not specify this option along with -float or hexcolor.
115 -nomap Generates the histogram for human reading. This is the default.
118 -colorname
121 Add the color name to the output. This is the name from the
122 system color dictionary ⟨libppm.html#dictionary⟩ . If the exact
123 color is not in the color dictionary, it is the closest color
124 that is in the dictionary and is preceded by a '*'. If you
125 don't have a system color dictionary, the program fails.
126 This option was added in Netpbm 10.10 (October 2002).
128 -noheader
131 Do not print the column headings.
132 -forensic
135 With this option, ppmhist works on images that contain invalid
137 sample values. Normally, like most Netpbm programs, ppmhist
138 fails if it encounters a sample value greater than the maxval
139 that the image declares. The presence of such a value means the
140 image is invalid, so the pixels have no meaning. But with
141 -forensic, ppmhist produces a histogram of the actual sample
142 values without regard to maxval. It issues messages summarizing
143 the invalid pixels if there are any.
144 One use for this is to diagnose the problem that caused the
146 invalid Netpbm image to exist.
147 There is a small exception to the ability of ppmhist to process
149 invalid pixels even with -forensic: it can never process a sam‐
150 ple value greater than 65535. Note that in the rarely used
151 Plain PPM format, it is possible for a number greater than that
152 to appear where a sample value belongs.
153 This option was new in Netpbm 10.66 (March 2014). But Netpbm
155 older than 10.66 does not properly reject invalid sample values,
156 so the effect is very similar to -forensic.
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162 ppm(1), pgmhist(1), pnmcolormap(1), pnmhistmap(1), ppmchange(1)
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166 Copyright (C) 1989 by Jef Poskanzer.
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169 This manual page was generated by the Netpbm tool 'makeman' from HTML
170 source. The master documentation is at
171 http://netpbm.sourceforge.net/doc/ppmhist.html
173netpbm documentation 24 August 2019 Ppmhist User Manual(0)