1RDJPGCOM(1) General Commands Manual RDJPGCOM(1)
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6 rdjpgcom - display text comments from a JPEG file
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9 rdjpgcom [ -raw ] [ -verbose ] [ filename ]
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12 rdjpgcom reads the named JPEG/JFIF file, or the standard input if no
13 file is named, and prints any text comments found in the file on the
14 standard output.
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16 The JPEG standard allows "comment" (COM) blocks to occur within a JPEG
17 file. Although the standard doesn't actually define what COM blocks
18 are for, they are widely used to hold user-supplied text strings. This
19 lets you add annotations, titles, index terms, etc to your JPEG files,
20 and later retrieve them as text. COM blocks do not interfere with the
21 image stored in the JPEG file. The maximum size of a COM block is 64K,
22 but you can have as many of them as you like in one JPEG file.
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25 -raw Normally rdjpgcom escapes non-printable characters in comments,
26 for security reasons. This option avoids that.
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28 -verbose Causes rdjpgcom to also display the JPEG image dimensions.
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30 Switch names may be abbreviated, and are not case sensitive.
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33 rdjpgcom does not depend on the IJG JPEG library. Its source code is
34 intended as an illustration of the minimum amount of code required to
35 parse a JPEG file header correctly.
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37 In -verbose mode, rdjpgcom will also attempt to print the contents of
38 any "APP12" markers as text. Some digital cameras produce APP12 mark‐
39 ers containing useful textual information. If you like, you can modify
40 the source code to print other APPn marker types as well.
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43 cjpeg(1), djpeg(1), jpegtran(1), wrjpgcom(1)
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46 Independent JPEG Group
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50 02 April 2009 RDJPGCOM(1)