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<refentry id="djpeg-1">
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<refmeta><refentrytitle>djpeg</refentrytitle><manvolnum>1</manvolnum>
<refmiscinfo class="date">26 Mar 2004</refmiscinfo>
<refmiscinfo class="sectdesc">&man1;</refmiscinfo>
<refmiscinfo class="software">&release;</refmiscinfo>
<refmiscinfo class="arch">generic</refmiscinfo>
<refmiscinfo class="copyright">&suncopy;</refmiscinfo>
</refmeta>
<indexterm><primary>djpeg</primary></indexterm><indexterm><primary>decompress
a JPEG file to an image file</primary></indexterm>
<refnamediv id="djpeg-1-name"><refname>djpeg</refname><refpurpose>decompress
a JPEG file to an image file</refpurpose></refnamediv>
<refsynopsisdiv id="djpeg-1-synp"><title>&synp-tt;</title>
<cmdsynopsis><command>&cmd;</command><arg choice="opt"><option role="nodash"><replaceable>
options</replaceable></option></arg><arg choice="opt"><option role="nodash"><replaceable>
filename</replaceable></option></arg>
</cmdsynopsis></refsynopsisdiv>
<refsect1 id="djpeg-1-desc"><title>&desc-tt;</title>
<para><command>&cmd;</command> decompresses the named JPEG file, or the standard
input if no file is named, and produces an image file on the standard output.
The following output file formats are currently supported:</para>
<itemizedlist>
<listitem><para>BMP</para></listitem>
<listitem><para>GIF</para></listitem>
<listitem><para>PGM, the PBMPLUS gray-scale format</para></listitem>
<listitem><para>PPM, the PBMPLUS color format</para></listitem>
<listitem><para>RLE, the Utah Raster Toolkit format</para></listitem>
<listitem><para>Targa</para></listitem>
</itemizedlist>
<para>RLE is supported only if the URT library is available.</para>
</refsect1>
<refsect1 id="djpeg-1-opts"><title>&opts-tt;</title>
<para>All options may be abbreviated. For example, <option>grayscale</option>
may be written <option>gray</option> or <option>gr</option>. Upper and lower
case are equivalent. For example, <option>BMP</option> is the same as <option>
bmp</option>. British spellings are also accepted. For example, <option>greyscale
</option>.</para>
<refsect2 id="djpeg-1-opts-basic">
<title>Basic Options</title>
<para>The following basic options are supported:</para>
<variablelist termlength="narrow">
<varlistentry><term><option>bmp</option></term><listitem><para>Specify that
the output file is in BMP format, Windows flavor. 8-bit colormapped format
is displayed if <option>colors</option> or <option>grayscale</option> is specified,
or if the JPEG file is grayscale. Otherwise, 24-bit full-color format is displayed.
</para>
</listitem></varlistentry>
<varlistentry><term><option>colors <replaceable>N</replaceable></option></term>
<listitem><para>Reduce the image to at most <replaceable>N</replaceable> colors.
This option reduces the number of colors used in the output image, so that
the output image can be displayed on a colormapped display or stored in a
colormapped file format. For example, if you have an 8-bit display, you must
reduce to 256 colors or less. </para>
<para>You can also use <option>quantize</option> to specify this option. However, <option>
colors</option> is the recommended option name. The <option>quantize</option>
option is provided only for backwards compatibility.</para>
</listitem></varlistentry>
<varlistentry><term><option>fast</option></term><listitem><para>Select the
recommended processing options for fast, low-quality output. The default options
are chosen for highest quality output. Currently, this is equivalent to <option>
dct fast</option> <option>nosmooth</option> <option>onepass</option> <option>
dither ordered</option>.</para>
</listitem></varlistentry>
<varlistentry><term><option>gif</option></term><listitem><para>Specify that
the output file is in GIF format. GIF does not support more than 256 colors,
so <option>colors 256</option> is assumed unless you specify a smaller number
of colors.</para>
</listitem></varlistentry>
<varlistentry><term><option>grayscale</option></term><listitem><para>Create
a monochrome image file even if the JPEG file is a color file. This option
is useful for viewing images on monochrome displays. <command>&cmd;</command>
runs noticeably faster in this mode.</para>
</listitem></varlistentry>
<varlistentry><term><option>os2</option></term><listitem><para>Specify that
the output file is in BMP format, OS/2 1.x flavor. 8-bit colormapped format
is displayed if <option>colors</option> or <option>grayscale</option> is specified,
or if the JPEG file is grayscale. Otherwise, 24-bit full-color format is displayed.
</para>
</listitem></varlistentry>
<varlistentry><term><option>pnm</option></term><listitem><para>Specify that
the output file is in PBMPLUS format. PGM format is displayed if <option>
grayscale</option> is specified, or if the JPEG file is grayscale. Otherwise,
PPM format is displayed.</para>
</listitem></varlistentry>
<varlistentry><term><option>rle</option></term><listitem><para>Specify that
the output file is in RLE format. This option requires the URT library.</para>
</listitem></varlistentry>
<varlistentry><term><option>scale <replaceable>M</replaceable>/<replaceable>
N</replaceable></option></term><listitem><para>Scale the output image by a
factor <replaceable>M</replaceable>/<replaceable>N</replaceable>. Currently,
the scale factor must be 1/1, 1/2, 1/4, or 1/8. Scaling is useful if the image
is larger than your screen. <command>&cmd;</command> runs much faster when
scaling down the output.</para>
</listitem></varlistentry>
<varlistentry><term><option>targa</option></term><listitem><para>Specify that
the output file is in Targa format. Grayscale format is displayed if <option>
grayscale</option> is specified, or if the JPEG file is grayscale. Colormapped
format is displayed if <option>colors</option> is specified. Otherwise, 24-bit
full-color format is displayed.</para>
</listitem></varlistentry>
</variablelist></refsect2>
<refsect2 id="djpeg-1-opts-int">
<title>Intermediate Options</title>
<para>The following intermediate options are supported:</para>
<variablelist termlength="narrow">
<varlistentry><term><option>dct fast</option></term><listitem><para>Use the
fast integer DCT method. This method is less accurate than the integer DCT
method or the floating-point DCT method.</para>
</listitem></varlistentry>
<varlistentry><term><option>dct float</option></term><listitem><para>Use the
floating-point DCT method. The float method is very slightly more accurate
than the int method, but is much slower unless your machine has very fast
floating-point hardware. The results of the floating-point method may vary
slightly across machines, while the integer methods should give the same results
everywhere.</para>
</listitem></varlistentry>
<varlistentry><term><option>dct int</option></term><listitem><para>Use the
integer DCT method. This is the default method.</para>
</listitem></varlistentry>
<varlistentry><term><option>dither fs</option></term><listitem><para>Use Floyd-Steinberg
dithering in color quantization. By default, Floyd-Steinberg dithering is
applied when quantizing colors. This process is slow but usually produces
the best results. This option has no effect unless color quantization is being
done.</para>
</listitem></varlistentry>
<varlistentry><term><option>dither none</option></term><listitem><para>Do
not use dithering in color quantization. No dithering is fast but is usually
of poor quality. This option has no effect unless color quantization is being
done.</para>
</listitem></varlistentry>
<varlistentry><term><option>dither ordered</option></term><listitem><para>
Use ordered dithering in color quantization. Ordered dither is a compromise
between speed and quality. Ordered dither is only available in <option>onepass
</option> mode. This option has no effect unless color quantization is being
done.</para>
</listitem></varlistentry>
<varlistentry><term><option>map <replaceable>file</replaceable></option></term>
<listitem><para>Quantize to the colors used in the specified image file. This
option is useful for producing multiple files with identical color maps, or
for forcing a predefined set of colors to be used. <replaceable>file</replaceable>
must be a GIF or PPM file. This option overrides the <option>colors</option>
and <option>onepass</option> options.</para>
</listitem></varlistentry>
<varlistentry><term><option>maxmemory <replaceable>N</replaceable></option></term>
<listitem><para>Set the limit for the amount of memory to use in processing
large images. <replaceable>N</replaceable> is specified in thousands of bytes,
or in millions of bytes if "M" is specified with the number. For example, <option>
max 4m</option> selects 4000000 bytes. If more space is needed, temporary
files are used.</para>
</listitem></varlistentry>
<varlistentry><term><option>nosmooth</option></term><listitem><para>Use a
faster, lower-quality upsampling routine.</para>
</listitem></varlistentry>
<varlistentry><term><option>onepass</option></term><listitem><para>Use one-pass
instead of two-pass color quantization. The one-pass method is faster and
requires less memory, but produces a lower-quality image. The <option>onepass
</option> option is ignored unless you also specify the <option>colors <replaceable>
N</replaceable></option> option. The one-pass method is always used for grayscale
output, the two-pass method provides no improvement for such output.</para>
</listitem></varlistentry>
<varlistentry><term><option>outfile <replaceable>name</replaceable></option></term>
<listitem><para>Send the output image to the named file, instead of to the
standard output.</para>
</listitem></varlistentry>
<varlistentry><term><option>verbose</option></term><listitem><para>Display
version information at startup, and enable debug printout. The <option>vv
</option> option displays more verbose output than the <option>v</option>
option. The <option>vvv</option> option displays the most verbose output.
You can also use <option>debug</option> to specify the verbose option.</para>
</listitem></varlistentry>
</variablelist></refsect2>
</refsect1>
<refsect1 id="djpeg-1-oper"><title>&oper-tt;</title>
<para>The following operands are supported:</para>
<variablelist termlength="narrow">
<varlistentry><term><option role="nodash"><replaceable>filename</replaceable></option></term>
<listitem><para>The name of the JPEG file to be decompressed.</para>
</listitem></varlistentry>
</variablelist></refsect1>
<refsect1 id="djpeg-1-exde"><title>&exde-tt;</title>
<refsect2 id="djpeg-1-exde-hints">
<title>Hints</title>
<para>To get a quick preview of an image, use the <option>grayscale</option>
or <option>scale</option> options, or a combination of both options. For example, <option>
grayscale</option> <option>scale 1/8</option> is the fastest case.</para>
<para>Several options trade image quality to gain speed. The <option>fast
</option> option configures the recommended settings.</para>
<para>The <option>dct fast</option> and <option>nosmooth</option> options
gain speed for a small sacrifice in quality. When producing a color-quantized
image, <option>onepass</option> <option>dither ordered</option> is fast but
much lower quality than the default behavior. <option>dither none</option>
may give acceptable results in two-pass mode, but is seldom tolerable in one-pass
mode. </para>
<para>If you have very fast floating point hardware, <option>dct float</option>
may be even faster than <option>dct fast</option>. However, on most machines, <option>
dct float</option> is slower than <option>dct int</option>. In such cases,
do not use <option>dct float</option>, because the theoretical accuracy advantage
is too small to be significant in practice.</para>
</refsect2>
</refsect1>
<refsect1 id="djpeg-1-exam"><title>&exam-tt;</title>
<example role="example">
<title>Decompressing the JPEG File test.jpg, Quantizing to 256 Colors, and
Saving the Output in 8–bit BMP Format as test.bmp</title>
</userinput></screen></para>
</example>
</refsect1>
<refsect1 id="djpeg-1-envr"><title>&envr-tt;</title>
<para><command>&cmd;</command> uses the following environment variables:</para>
<variablelist>
<varlistentry><term>JPEGMEM</term><listitem><para>The value of this environment
variable, if set, is the default memory limit. The value is specified as described
for the <option>maxmemory</option> option. JPEGMEM overrides the default value
specified when the program was compiled, and is in turn overridden by an explicit <option>
maxmemory</option> option.</para>
</listitem></varlistentry>
</variablelist></refsect1>
<refsect1 id="djpeg-1-attr"><title>&attr-tt;</title>
<para>See <olink targetdocent="REFMAN5" localinfo="attributes-5"><citerefentry>
<refentrytitle>attributes</refentrytitle><manvolnum>5</manvolnum></citerefentry></olink>
for descriptions of the following attributes:</para>
<informaltable frame="all">
<tgroup cols="2" colsep="1" rowsep="1"><colspec colname="COLSPEC0" colwidth="1*">
<colspec colname="COLSPEC1" colwidth="1*">
<thead>
<row><entry align="center" valign="middle">ATTRIBUTE TYPE</entry><entry align="center"
valign="middle">ATTRIBUTE VALUE</entry></row>
</thead>
<tbody>
</row>
<row><entry colname="COLSPEC0"><para>Interface stability</para></entry><entry
colname="COLSPEC1"><para>Uncommitted</para></entry></row>
</tbody>
</tgroup>
</informaltable>
</refsect1>
<refsect1 id="djpeg-1-also"><title>&also-tt;</title>
<!--Reference to another man page-->
<!--Reference to a Help manual-->
<!--Reference to a book.-->
<para>Wallace, Gregory K., <citetitle>The JPEG Still Picture Compression Standard
</citetitle> Communications of the ACM, April 1991 (vol. 34, no. 4), pp. 30-44.
</para>
<para><citerefentry><refentrytitle>cjpeg</refentrytitle><manvolnum>1</manvolnum>
</citerefentry>, <citerefentry><refentrytitle>jpegtran</refentrytitle><manvolnum>
1</manvolnum></citerefentry>, <citerefentry><refentrytitle>rdjpgcom</refentrytitle>
<manvolnum>1</manvolnum></citerefentry>, <citerefentry><refentrytitle>wrjpgcom
</refentrytitle><manvolnum>1</manvolnum></citerefentry></para>
</refsect1>
<refsect1 id="djpeg-1-note"><title>¬e-tt;</title>
<para>Arithmetic coding is not supported. <command>&cmd;</command> produces
uncompressed GIF files. These large files are readable by standard GIF decoders.
</para>
<para>This man page was originally written by the Independent JPEG Group.
Updated by Breda McColgan, Sun Microsystems Inc., 2004. </para>
</refsect1>
</refentry>