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. frequency means to list them in order of
76 how pixels in the input image have the color, with the most rep‐
77 resented colors first. rgb means to sort them first by the
78 intensity of the red component of the color, then of the green,
79 then of the blue, with the least intense first.
80 The default is frequency.
82 -hexcolor
85 Print the color components in hexadecimal. See output format
86 ⟨#output⟩ .
87 You may not specify this option along with -float or map.
89 -float Print the color components and the luminosity as floating point
92 numbers in the range [0,1]. See output format ⟨#output⟩ .
93 You may not specify this option along with -hexcolor or map.
95 This option was added in Netpbm 10.19 (November 2003).
97 -map Generates a PPM file of the colormap for the image, with the
100 color histogram as comments. See output format ⟨#output⟩ .
101 You may not specify this option along with -float or hexcolor.
103 -nomap Generates the histogram for human reading. This is the default.
106 -colorname
109 Add the color name to the output. This is the name from the
110 system color dictionary ⟨libppm.html#rgb.txt⟩ . If the exact
111 color is not in the color dictionary, it is the closest color
112 that is in the dictionary and is preceded by a '*'. If you
113 don't have a system color dictionary, the program fails.
114 This option was added in Netpbm 10.10 (October 2002).
116 -noheader
119 Do not print the column headings.
120 -forensic
123 With this option, ppmhist works on images that contain invalid
125 sample values. Normally, like most Netpbm programs, ppmhist
126 fails if it encounters a sample value greater than the maxval
127 that the image declares. The presence of such a value means the
128 image is invalid, so the pixels have no meaning. But with
129 -forensic, ppmhist produces a histogram of the actual sample
130 values without regard to maxval. It issues messages summarizing
131 the invalid pixels if there are any.
132 One use for this is to diagnose the problem that caused the
134 invalid Netpbm image to exist.
135 There is a small exception to the ability of ppmhist to process
137 invalid pixels even with -forensic: it can never process a sam‐
138 ple value greater than 65535. Note that in the rarely used
139 Plain PPM format, it is possible for a number greater than that
140 to appear where a sample value belongs.
141 This option was new in Netpbm 10.66 (March 2014). But Netpbm
143 older than 10.66 does not properly reject invalid sample values,
144 so the effect is very similar to -forensic.
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150 ppm(1), pgmhist(1), pnmcolormap(1), pnmhistmap(1), ppmchange(1)
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154 Copyright (C) 1989 by Jef Poskanzer.
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157 This manual page was generated by the Netpbm tool 'makeman' from HTML
158 source. The master documentation is at
159 http://netpbm.sourceforge.net/doc/ppmhist.html
161netpbm documentation 15 August 2015 Ppmhist User Manual(0)