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HDF5/H5Z API Specification
</title>
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<h1>H5Z: Filter and Compression Interface</h1>
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<h2>Filter and Compression API Functions</h2>
These functions enable the user to configure new filters
for the local environment.
<table border=0 width=80%>
<tr><td valign=top width="30%">
<ul>
<li><a href="#Compression-FilterAvail">H5Zfilter_avail</a><br>
<li><a href="#Compression-GetFilterInfo">H5Zget_filter_info</a>
</ul>
</td><td> </td><td valign=top width="30%">
<ul>
<li><a href="#Compression-Register">H5Zregister</a>
</ul>
</td><td> </td><td valign=top width="30%">
<ul>
<li><a href="#Compression-Unregister">H5Zunregister</a>
</ul>
</td></tr>
</table>
<br>
<strong>The FORTRAN90 Interfaces:</strong>
<br>
In general, each FORTRAN90 subroutine performs exactly the same task
as the corresponding C function.
<br>
<table border=0 width=80%>
<tr><td valign=top width="30%">
<ul>
<li><a href="#Compression-FilterAvail">h5zfilter_avail_f</a>
</ul>
</td><td> </td><td valign=top width="30%">
<ul>
<!--<li><a href="#Compression-Register">h5zregister_f</a><br> -->
<li><a href="#Compression-GetFilterInfo">h5zget_filter_info_f</a>
</ul>
</td><td> </td><td valign=top width="30%">
<ul>
<li><a href="#Compression-Unregister">h5zunregister_f</a>
</ul>
</td></tr>
</table>
<p>
HDF5 supports a filter pipeline that provides the capability for standard
and customized raw data processing during I/O operations.
HDF5 is distributed with a small set of standard filters such as
compression (gzip, SZIP, and a shuffling algorithm) and
error checking (Fletcher32 checksum).
For further flexibility, the library allows a
user application to extend the pipeline through the
creation and registration of customized filters.
<p>
The flexibility of the filter pipeline implementation enables the
definition of additional filters by a user application.
A filter
<ul>
<li>is associated with a dataset when the dataset is created,
<li>can be used only with chunked data
<br>(i.e., datasets stored in the <code>H5D_CHUNKED</code>
storage layout), and
<li>is applied independently to each chunk of the dataset.
</ul>
<p>
The HDF5 library does not support filters for contiguous datasets
because of the difficulty of implementing random access for partial I/O.
Compact dataset filters are not supported because it would not produce
significant results.
<p>
Filter identifiers for the filters distributed with the HDF5 Library
are as follows:
<table align=center border=0>
<tr valign=top align=left>
<td>
<code>H5Z_FILTER_DEFLATE</code></td><td>The gzip compression,
or deflation, filter
</td></tr><tr><td>
<code>H5Z_FILTER_SZIP</code></td><td>The SZIP compression filter
</td></tr><tr><td>
<code>H5Z_FILTER_SHUFFLE</code></td><td>The shuffle algorithm filter
</td></tr><tr><td>
<code>H5Z_FILTER_FLETCHER32 </code></td><td>The Fletcher32 checksum,
or error checking, filter
</td></tr>
</table>
Custom filters that have been registered with the library will have
additional unique identifiers.
<p>
See <a href="Datasets.html"><cite>The Dataset Interface (H5D)</cite></a>
in the <cite>HDF5 User's Guide</cite> for further information regarding
data compression.
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Describes HDF5 Release 1.6.10, November 2009
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