203 lines
6.5 KiB
Markdown
203 lines
6.5 KiB
Markdown
<refmeta>
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<refentrytitle>Image pyramids</refentrytitle>
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<manvolnum>3</manvolnum>
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<refmiscinfo>libvips</refmiscinfo>
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</refmeta>
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<refnamediv>
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<refname>Pyramids</refname>
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<refpurpose>How to use libvips to make image pyramids</refpurpose>
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</refnamediv>
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libvips includes `vips_dzsave()`, an operation
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that can build image pyramids compatible with <ulink
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url="http://en.wikipedia.org/wiki/Deep_Zoom">DeepZoom</ulink>, Zoomify
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and <ulink url="https://developers.google.com/maps">Google Maps</ulink>
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image viewers. It's fast and can generate pyramids for large images using
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only a small amount of memory.
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The TIFF writer, `vips_tiffsave()` can also build tiled pyramidal TIFF images,
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but that's very simple to use. This page concentrates on the DeepZoom builder.
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Run dzsave with no arguments to see a summary:
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```
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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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```
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You can also call `vips_dzsave()` from any language with a libvips binding, or
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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
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`--layout`, dzsave writes DeepZoom pyramids. For example:
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```
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$ vips dzsave huge.tif mydz
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```
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This will create a directory called `mydz_files` containing the image
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tiles, and write a file called `mydz.dzi` containing the image
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metadata.
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You can use the `--suffix` option to control how tiles are written. For
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example:
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```
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$ vips dzsave huge.tif mydz --suffix .jpg[Q=90]
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```
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will write JPEG tiles with the quality factor set to 90. You can set any
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format write options you like, see the API docs for `vips_jpegsave()`
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for details.
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# Writing Zoomify pyramids
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Use `--layout zoomify` to put dzsave into zoomify mode. For example:
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```
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$ vips dzsave huge.tif myzoom --layout zoomify
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```
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This will create a directory called `myzoom` containing a file called
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`ImageProperties.xml` with the image metadata in, and a series of
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directories called `TileGroupn`, each containing 256 image tiles.
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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
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example:
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```
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$ vips dzsave wtc.tif gmapdir --layout google
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```
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Will create a directory called `gmapdir` containing `blank.png`, the
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file to display for blank tiles, and a set of numbered directories, one
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for each zoom level. The pyramid can be sparse (blank tiles are not
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written).
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As with DeepZoom, you can use `--suffix` to set jpeg quality.
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Use `--background` to set the background colour. This is the colour
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displayed for bits of the pyramid not in the image (image edges, for
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example). By default, the image background is white.
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Use `--centre` to add a border to the image large enough to centre the
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image within the lowest resolution tile. By default, images are not
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centred.
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For example:
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```
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$ vips dzsave wtc.tif gmapdir --layout google --background 0 --centre
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```
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# Other options
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You can use `--tile-size` and `--overlap` to control how large the tiles
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are and how they overlap (obviously). They default to the correct values
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for the selected layout.
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You can use `--depth` to control how deep the pyramid should be. Possible
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values are `onepixel`, `onetile` and `one`. `onepixel` means the image
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is shrunk until it fits within a single pixel. `onetile` means shrink
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until it fits with a tile. `one` means only write one pyramid layer (the
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highest resolution one). It defaults to the correct value for the selected
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layout. `--depth one` is handy for slicing up a large image into tiles
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(rather than a pyramid).
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You can use `--angle` to do a 90, 180 or 270 degree rotate of an image
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during pyramid write.
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You can use `--container` to set the container type. Normally dzsave will
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write a tree of directories, but with `--container zip` you'll get a zip file
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instead. Use .zip as the directory suffix to turn on zip format automatically:
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```
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$ vips dzsave wtc.tif mypyr.zip
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```
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to write a zipfile containing the tiles. You can use `.szi` as a suffix to
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enable zip output as well.
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Use `--properties` to output an XML file called `vips-properties.xml`. This
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contains a dump of all the metadata vips has about the image as a set of
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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
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`vips_dzsave()`. This means you can write the output of any vips operation to a
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pyramid. For example:
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```
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$ vips extract_area huge.svs mypy.dz[layout=google] 100 100 10000 10000
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```
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The arguments to `extract_area` are image-in, image-out, left, top,
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width, height. So this command will cut out a 10,000 by 10,000 pixel
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area from near the top-left-hand corner of an Aperio slide image, then
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build a pyramid in Google layout using just those pixels.
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If you are working from OpenSlide images, you can use the shrink-on-load
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feature of many of those formats. For example:
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```
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$ vips dzsave CMU-1.mrxs[level=1] x
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```
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Will pull out level 1 (the half-resolution level of an MRXS slide) and
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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
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the end of configure carefully. You must have the `libgsf-1-dev` package
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for `vips_dzsave()` to work.
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