Image pyramids

3 libvips

Pyramids

How to use libvips to make image pyramids

libvips includes `vips_dzsave()`, an operation that can build image pyramids compatible with DeepZoom, Zoomify and Google Maps image viewers. It's fast and can generate pyramids for large images using only a small amount of memory. 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. # Writing DeepZoom pyramids 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. # Writing Zoomify pyramids 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. # Writing Google Maps pyramids Use `--layout google` to write Google maps-style pyramids. These are compatible with Leaflet. For example: ``` $ 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 ``` # Other options 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. # Preprocessing images 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. # Troubleshooting 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.