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 -sort={frequency,rgb}
74 The -sort option determines the order in which the colors are
75 listed in the output. rgb means to sort them first by the
76 intensity of the red component of the color, then of the green,
77 then of the blue, with the least intense first. frequency means
78 to list them in order of how many pixels in the input image have
79 the color, with the most represented colors first. Among colors
80 with the same frequency, the order is the same as with rgb.
81 The default is frequency.
83 Before Netpbm 10.88 (September 2019), with -sort=frequency, the
85 order of colors that have the same frequency is arbitrary.
86 -hexcolor
89 Print the color components in hexadecimal. See output format
90 ⟨#output⟩ .
91 You may not specify this option along with -float or map.
93 -float Print the color components and the luminosity as floating point
96 numbers in the range [0,1]. See output format ⟨#output⟩ .
97 You may not specify this option along with -hexcolor or map.
99 This option was added in Netpbm 10.19 (November 2003).
101 -map Generates a PPM file of the colormap for the image, with the
104 color histogram as comments. See output format ⟨#output⟩ .
105 You may not specify this option along with -float or hexcolor.
107 -nomap Generates the histogram for human reading. This is the default.
110 -colorname
113 Add the color name to the output. This is the name from the
114 system color dictionary ⟨libppm.html#rgb.txt⟩ . If the exact
115 color is not in the color dictionary, it is the closest color
116 that is in the dictionary and is preceded by a '*'. If you
117 don't have a system color dictionary, the program fails.
118 This option was added in Netpbm 10.10 (October 2002).
120 -noheader
123 Do not print the column headings.
124 -forensic
127 With this option, ppmhist works on images that contain invalid
129 sample values. Normally, like most Netpbm programs, ppmhist
130 fails if it encounters a sample value greater than the maxval
131 that the image declares. The presence of such a value means the
132 image is invalid, so the pixels have no meaning. But with
133 -forensic, ppmhist produces a histogram of the actual sample
134 values without regard to maxval. It issues messages summarizing
135 the invalid pixels if there are any.
136 One use for this is to diagnose the problem that caused the
138 invalid Netpbm image to exist.
139 There is a small exception to the ability of ppmhist to process
141 invalid pixels even with -forensic: it can never process a sam‐
142 ple value greater than 65535. Note that in the rarely used
143 Plain PPM format, it is possible for a number greater than that
144 to appear where a sample value belongs.
145 This option was new in Netpbm 10.66 (March 2014). But Netpbm
147 older than 10.66 does not properly reject invalid sample values,
148 so the effect is very similar to -forensic.
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154 ppm(1), pgmhist(1), pnmcolormap(1), pnmhistmap(1), ppmchange(1)
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158 Copyright (C) 1989 by Jef Poskanzer.
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161 This manual page was generated by the Netpbm tool 'makeman' from HTML
162 source. The master documentation is at
163 http://netpbm.sourceforge.net/doc/ppmhist.html
165netpbm documentation 24 August 2019 Ppmhist User Manual(0)