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63 lines
1.7 KiB
63 lines
1.7 KiB
.TH RDJPGCOM 1 "13 September 2013" |
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.SH NAME |
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rdjpgcom \- display text comments from a JPEG file |
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.SH SYNOPSIS |
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.B rdjpgcom |
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[ |
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.B \-raw |
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] |
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[ |
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.B \-verbose |
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] |
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[ |
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.I filename |
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] |
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.LP |
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.SH DESCRIPTION |
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.LP |
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.B rdjpgcom |
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reads the named JPEG/JFIF file, or the standard input if no file is named, |
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and prints any text comments found in the file on the standard output. |
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.PP |
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The JPEG standard allows "comment" (COM) blocks to occur within a JPEG file. |
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Although the standard doesn't actually define what COM blocks are for, they |
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are widely used to hold user-supplied text strings. This lets you add |
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annotations, titles, index terms, etc to your JPEG files, and later retrieve |
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them as text. COM blocks do not interfere with the image stored in the JPEG |
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file. The maximum size of a COM block is 64K, but you can have as many of |
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them as you like in one JPEG file. |
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.SH OPTIONS |
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.TP |
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.B \-raw |
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Normally |
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.B rdjpgcom |
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escapes non-printable characters in comments, for security reasons. |
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This option avoids that. |
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.PP |
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.B \-verbose |
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Causes |
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.B rdjpgcom |
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to also display the JPEG image dimensions. |
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.PP |
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Switch names may be abbreviated, and are not case sensitive. |
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.SH HINTS |
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.B rdjpgcom |
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does not depend on the IJG JPEG library. Its source code is intended as an |
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illustration of the minimum amount of code required to parse a JPEG file |
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header correctly. |
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.PP |
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In |
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.B \-verbose |
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mode, |
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.B rdjpgcom |
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will also attempt to print the contents of any "APP12" markers as text. |
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Some digital cameras produce APP12 markers containing useful textual |
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information. If you like, you can modify the source code to print |
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other APPn marker types as well. |
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.SH SEE ALSO |
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.BR cjpeg (1), |
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.BR djpeg (1), |
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.BR jpegtran (1), |
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.BR wrjpgcom (1) |
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.SH AUTHOR |
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Independent JPEG Group
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