libvips/doc/Making-image-pyramids.md

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<refmeta>
<refentrytitle>Image pyramids</refentrytitle>
<manvolnum>3</manvolnum>
<refmiscinfo>libvips</refmiscinfo>
</refmeta>
<refnamediv>
<refname>Pyramids</refname>
<refpurpose>How to use libvips to make image pyramids</refpurpose>
</refnamediv>
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libvips includes `vips_dzsave()`, 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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The TIFF writer, `vips_tiffsave()` can also build tiled pyramidal TIFF images,
but that's very simple to use. This page concentrates on the DeepZoom builder.
Run dzsave with no arguments to see a summary:
```
$ vips dzsave
save image to deepzoom file
usage:
dzsave in filename
where:
in - Image to save, input VipsImage
filename - Filename to save to, input gchararray
optional arguments:
basename - Base name to save to, input gchararray
layout - Directory layout, input VipsForeignDzLayout
default: dz
allowed: dz, zoomify, google
suffix - Filename suffix for tiles, input gchararray
overlap - Tile overlap in pixels, input gint
default: 1
min: 0, max: 8192
tile-size - Tile size in pixels, input gint
default: 254
min: 1, max: 8192
centre - Center image in tile, input gboolean
default: false
depth - Pyramid depth, input VipsForeignDzDepth
default: onepixel
allowed: onepixel, onetile, one
angle - Rotate image during save, input VipsAngle
default: d0
allowed: d0, d90, d180, d270
container - Pyramid container type, input VipsForeignDzContainer
default: fs
allowed: fs, zip
properties - Write a properties file to the output directory, input
gboolean
default: false
compression - ZIP deflate compression level, input gint
default: 0
min: -1, max: 9
strip - Strip all metadata from image, input gboolean
default: false
background - Background value, input VipsArrayDouble
operation flags: sequential nocache
```
You can also call `vips_dzsave()` from any language with a libvips binding, or
by using `.dz` or `.szi` as an output file suffix.
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# Writing DeepZoom pyramids
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The `--layout` option sets the basic mode of operation. With no
`--layout`, dzsave writes DeepZoom pyramids. For example:
```
$ vips dzsave huge.tif mydz
```
This will create a directory called `mydz_files` containing the image
tiles, and write a file called `mydz.dzi` containing the image
metadata. 
You can use the `--suffix` option to control how tiles are written. For
example:
```
$ vips dzsave huge.tif mydz --suffix .jpg[Q=90]
```
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 `vips_jpegsave()`
for details.
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# Writing Zoomify pyramids
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Use `--layout zoomify` to put dzsave into zoomify mode. For example:
```
$ vips dzsave huge.tif myzoom --layout zoomify
```
This will create a directory called `myzoom` containing a file called
`ImageProperties.xml` with the image metadata in, and a series of
directories called `TileGroupn`, each containing 256 image tiles.
As with DeepZoom, you can use `--suffix` to set jpeg quality.
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# Writing Google Maps pyramids
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Use `--layout google` to write Google maps-style pyramids. These are
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compatible with <ulink url="http://leafletjs.com">Leaflet</ulink>. For
example:
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```
$ vips dzsave wtc.tif gmapdir --layout google
```
Will create a directory called `gmapdir` containing `blank.png`, 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).
As with DeepZoom, you can use `--suffix` to set jpeg quality.
Use `--background` 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.
Use `--centre` to add a border to the image large enough to centre the
image within the lowest resolution tile. By default, images are not
centred.
For example:
```
$ vips dzsave wtc.tif gmapdir --layout google --background 0 --centre
```
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# Other options
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You can use `--tile-size` and `--overlap` to control how large the tiles
are and how they overlap (obviously). They default to the correct values
for the selected layout.
You can use `--depth` to control how deep the pyramid should be. Possible
values are `onepixel`, `onetile` and `one`. `onepixel` means the image
is shrunk until it fits within a single pixel. `onetile` means shrink
until it fits with a tile. `one` means only write one pyramid layer (the
highest resolution one). It defaults to the correct value for the selected
layout. `--depth one` is handy for slicing up a large image into tiles
(rather than a pyramid).
You can use `--angle` to do a 90, 180 or 270 degree rotate of an image
during pyramid write.
You can use `--container` to set the container type. Normally dzsave will
write a tree of directories, but with `--container zip` you'll get a zip file
instead. Use .zip as the directory suffix to turn on zip format automatically:
```
$ vips dzsave wtc.tif mypyr.zip
```
to write a zipfile containing the tiles. You can use `.szi` as a suffix to
enable zip output as well.
Use `--properties` to output an XML file called `vips-properties.xml`. 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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# Preprocessing images
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You can use `.dz` as a filename suffix, meaning send the image to
`vips_dzsave()`. This means you can write the output of any vips operation to a
pyramid. For example:
```
$ vips extract_area huge.svs mypy.dz[layout=google] 100 100 10000 10000
```
The arguments to `extract_area` 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.
If you are working from OpenSlide images, you can use the shrink-on-load
feature of many of those formats. For example:
```
$ vips dzsave CMU-1.mrxs[level=1] x
```
Will pull out level 1 (the half-resolution level of an MRXS slide) and
make a pyramid from that.
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# Troubleshooting
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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 `libgsf-1-dev` package
for `vips_dzsave()` to work.