184 lines
8.9 KiB
XML
184 lines
8.9 KiB
XML
<?xml version="1.0" encoding="utf-8" ?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
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<refentry id="Making-image-pyramids.md">
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<para>
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<refmeta> <refentrytitle>Image pyramids</refentrytitle> <manvolnum>3</manvolnum> <refmiscinfo>libvips</refmiscinfo> </refmeta>
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</para>
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<para>
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<refnamediv> <refname>Pyramids</refname> <refpurpose>How to use libvips to make image pyramids</refpurpose> </refnamediv>
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</para>
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<para>
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libvips includes <literal>vips_dzsave()</literal>, an operation that can build image pyramids compatible with <ulink url="http://en.wikipedia.org/wiki/Deep_Zoom">DeepZoom</ulink>, Zoomify and <ulink url="https://developers.google.com/maps/">Google Maps</ulink> image viewers. It’s fast and can generate pyramids for large images using only a small amount of memory.
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</para>
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<para>
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The TIFF writer, <literal>vips_tiffsave()</literal> can also build tiled pyramidal TIFF images, but that’s very simple to use. This page concentrates on the DeepZoom builder.
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</para>
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<para>
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Run dzsave with no arguments to see a summary:
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</para>
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<programlisting>
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$ vips dzsave
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save image to deepzoom file
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usage:
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dzsave in filename
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where:
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in - Image to save, input VipsImage
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filename - Filename to save to, input gchararray
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optional arguments:
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basename - Base name to save to, input gchararray
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layout - Directory layout, input VipsForeignDzLayout
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default: dz
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allowed: dz, zoomify, google
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suffix - Filename suffix for tiles, input gchararray
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overlap - Tile overlap in pixels, input gint
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default: 1
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min: 0, max: 8192
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tile-size - Tile size in pixels, input gint
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default: 254
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min: 1, max: 8192
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centre - Center image in tile, input gboolean
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default: false
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depth - Pyramid depth, input VipsForeignDzDepth
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default: onepixel
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allowed: onepixel, onetile, one
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angle - Rotate image during save, input VipsAngle
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default: d0
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allowed: d0, d90, d180, d270
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container - Pyramid container type, input VipsForeignDzContainer
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default: fs
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allowed: fs, zip
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properties - Write a properties file to the output directory, input
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gboolean
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default: false
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compression - ZIP deflate compression level, input gint
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default: 0
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min: -1, max: 9
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strip - Strip all metadata from image, input gboolean
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default: false
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background - Background value, input VipsArrayDouble
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operation flags: sequential nocache
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</programlisting>
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<para>
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You can also call <literal>vips_dzsave()</literal> from any language with a libvips binding, or by using <literal>.dz</literal> or <literal>.szi</literal> as an output file suffix.
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</para>
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<refsect3 id="writing-deepzoom-pyramids">
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<title>Writing <ulink url="http://en.wikipedia.org/wiki/Deep_Zoom">DeepZoom</ulink> pyramids</title>
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<para>
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The <literal>--layout</literal> option sets the basic mode of operation. With no <literal>--layout</literal>, dzsave writes DeepZoom pyramids. For example:
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</para>
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<programlisting>
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$ vips dzsave huge.tif mydz
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</programlisting>
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<para>
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This will create a directory called <literal>mydz_files</literal> containing the image tiles, and write a file called <literal>mydz.dzi</literal> containing the image metadata.
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</para>
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<para>
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You can use the <literal>--suffix</literal> option to control how tiles are written. For example:
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</para>
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<programlisting>
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$ vips dzsave huge.tif mydz --suffix .jpg[Q=90]
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</programlisting>
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<para>
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will write JPEG tiles with the quality factor set to 90. You can set any format write options you like, see the API docs for <literal>vips_jpegsave()</literal> for details.
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</para>
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</refsect3>
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<refsect3 id="writing-zoomify-pyramids">
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<title>Writing Zoomify pyramids</title>
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<para>
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Use <literal>--layout zoomify</literal> to put dzsave into zoomify mode. For example:
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</para>
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<programlisting>
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$ vips dzsave huge.tif myzoom --layout zoomify
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</programlisting>
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<para>
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This will create a directory called <literal>myzoom</literal> containing a file called <literal>ImageProperties.xml</literal> with the image metadata in, and a series of directories called <literal>TileGroupn</literal>, each containing 256 image tiles.
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</para>
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<para>
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As with DeepZoom, you can use <literal>--suffix</literal> to set jpeg quality.
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</para>
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</refsect3>
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<refsect3 id="writing-google-maps-pyramids">
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<title>Writing <ulink url="https://developers.google.com/maps/">Google Maps</ulink> pyramids</title>
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<para>
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Use <literal>--layout google</literal> to write Google maps-style pyramids. These are compatible with <ulink url="http://leafletjs.com/">leaflet</ulink>. For example:
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</para>
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<programlisting>
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$ vips dzsave wtc.tif gmapdir --layout google
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</programlisting>
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<para>
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Will create a directory called <literal>gmapdir</literal> containing <literal>blank.png</literal>, the file to display for blank tiles, and a set of numbered directories, one for each zoom level. The pyramid can be sparse (blank tiles are not written).
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</para>
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<para>
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As with DeepZoom, you can use <literal>--suffix</literal> to set jpeg quality.
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</para>
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<para>
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Use <literal>--background</literal> to set the background colour. This is the colour displayed for bits of the pyramid not in the image (image edges, for example). By default, the image background is white.
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</para>
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<para>
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Use <literal>--centre</literal> to add a border to the image large enough to centre the image within the lowest resolution tile. By default, images are not centred.
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</para>
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<para>
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For example:
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</para>
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<programlisting>
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$ vips dzsave wtc.tif gmapdir --layout google --background 0 --centre
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</programlisting>
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</refsect3>
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<refsect3 id="other-options">
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<title>Other options</title>
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<para>
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You can use <literal>--tile-size</literal> and <literal>--overlap</literal> to control how large the tiles are and how they overlap (obviously). They default to the correct values for the selected layout.
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</para>
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<para>
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You can use <literal>--depth</literal> to control how deep the pyramid should be. Possible values are <literal>onepixel</literal>, <literal>onetile</literal> and <literal>one</literal>. <literal>onepixel</literal> means the image is shrunk until it fits within a single pixel. <literal>onetile</literal> means shrink until it fits with a tile. <literal>one</literal> means only write one pyramid layer (the highest resolution one). It defaults to the correct value for the selected layout. <literal>--depth one</literal> is handy for slicing up a large image into tiles (rather than a pyramid).
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</para>
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<para>
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You can use <literal>--angle</literal> to do a 90, 180 or 270 degree rotate of an image during pyramid write.
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</para>
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<para>
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You can use <literal>--container</literal> to set the container type. Normally dzsave will write a tree of directories, but with <literal>--container zip</literal> you’ll get a zip file instead. Use .zip as the directory suffix to turn on zip format automatically:
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</para>
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<programlisting>
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$ vips dzsave wtc.tif mypyr.zip
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</programlisting>
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<para>
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to write a zipfile containing the tiles. You can use <literal>.szi</literal> as a suffix to enable zip output as well.
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</para>
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<para>
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Use <literal>--properties</literal> to output an XML file called <literal>vips-properties.xml</literal>. This contains a dump of all the metadata vips has about the image as a set of name-value pairs. It’s handy with openslide image sources.
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</para>
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</refsect3>
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<refsect3 id="preprocessing-images">
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<title>Preprocessing images</title>
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<para>
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You can use <literal>.dz</literal> as a filename suffix, meaning send the image to <literal>vips_dzsave()</literal>. This means you can write the output of any vips operation to a pyramid. For example:
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</para>
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<programlisting>
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$ vips extract_area huge.svs mypy.dz[layout=google] 100 100 10000 10000
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</programlisting>
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<para>
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The arguments to <literal>extract_area</literal> are image-in, image-out, left, top, width, height. So this command will cut out a 10,000 by 10,000 pixel area from near the top-left-hand corner of an Aperio slide image, then build a pyramid in Google layout using just those pixels.
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</para>
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<para>
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If you are working from OpenSlide images, you can use the shrink-on-load feature of many of those formats. For example:
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</para>
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<programlisting>
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$ vips dzsave CMU-1.mrxs[level=1] x
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</programlisting>
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<para>
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Will pull out level 1 (the half-resolution level of an MRXS slide) and make a pyramid from that.
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</para>
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</refsect3>
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<refsect3 id="troubleshooting">
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<title>Troubleshooting</title>
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<para>
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If you are building vips from source you do need to check the summary at the end of configure carefully. You must have the <literal>libgsf-1-dev</literal> package for <literal>vips_dzsave()</literal> to work.
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</para>
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</refsect3>
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</refentry>
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