Image viewer

Chaise 2D image viewer utilizes OpenSeadragon to provide support for:

  • Greyscale and RGB images. If an image is marked as greyscale, data modelers can define a default pseudo color that will be used to add color to the image properly. Users can change that color using the appropriate channel UI.
  • Single or multiple channel images. In the case of multi-channel images, the viewer app will blend the images. Users can toggle images and manipulate the blending.
  • Image annotations that overlay on top of main images. The viewer app will fetch and display the annotations if data modelers have appropriately configured the application. Users can also edit, delete, or create new annotations.
  • Multi-z images. If data modelers have properly configured the application, the viewer app provides a mechanism to navigate through the z-plane to display the images with different z-indices.
  • IIIF, DZI, and other browser compatible images. The viewer app uses the location of the images to find the appropriate mechanism to fetch the image based on their types. In the case of IIIF images, the proper image API will be used for fetching the tile images, while DZI relies on precomputed tile images in the file system.


Apart from other chaise dependencies, viewer app depends on the openseadragon-viewer as well.


You need to deploy both Chaise and openseadragon-viewer to ensure the viewer app is properly installed. The following are the steps to install both packages:

  1. First, you need to set up some environment variables. The following are the variables and their default values,

    • All the variables MUST have a trailing /.
    • If you’re installing remotely, since we’re using the WEB_INSTALL_ROOT in rsync command, you can use a remote location username@host:public_html/ for this variable.

    Which means,

    • Chaise build folder will be copied to /var/www/html/chaise/ location.
    • The URL path to access Chaise is /chaise/.
    • openseadragon-viewer build folder will be copied to /var/www/html/openseadragon-viewer/ location.
    • The URL path to access openseadragon-viewer is /openseadragon-viewer/.

    If that is not the case in your deployment, you should modify the variables accordingly.

  2. Make sure Chaise is deployed by following its own guide.

  3. Clone the openseadragon-viewer repository,

    $ git clone
  4. Run the following command in the openseadragon-viewer folder (make sure to run this in the openseadragon-viewer folder),

    $ make deploy

How it works

Chaise viewer app uses ERMrest to fetch the proper metadata and utilizes openseadragon-viewer to render the fetched imaging metadata and provide UI tools so users can interact with the image. To use openseadragon-viewer, the viewer app must provide some parameters. The following are different sources for deriving these parameters:

  • URL query parameters that are passed to the viewer app. URL query parameters have priority over other ways of providing parameters and override the behavior.
  • Metadata stored in ERMrest. For more information about the expected database models, please refer to configuration document.

Query parameters

Different browsers have different rules about the length limitation of query parameters. Users can also manipulate the query parameters. So we generally advise against the usage of query parameters. Although, in some cases, query parameters are the most convenient way to use the viewer app. For example:

  • The required model and metadata are not defined in the database, and you just want to show an image without the extra features (Refer to viewer-config.js documentation for more information about the required model structure.)
  • You want to override the default behavior and show only a small set of images or annotations. For example, assume that in the database the image has multiple annotations, and you just want to show that one specific annotation on a record page. You can provide an iframe with a query parameter that specifies the annotation URL.
  • For debugging or testing.
  • Modifying the default value of a general parameter.

Query parameters will be passed without any modification to the openseadragon-viewer. So you can use any of the parameters that are defined in the openseadragon-viewer usage document. There are two categories of parameters:

  • Channel parameters: these parameters provide information about the image channel. The main channel parameter is url. The value of this parameter must be the location of the image file (info.json, ImageProperties.xml, etc.), and if present, we will ignore the data stored in the database.
  • General parameters: parameters that will not affect the actual displayed image data and will modify other parts of the page. These parameters can be used in conjunction with image data stored in the database.
The actual image (channel) information will only come from the query parameter or database. If the image channel url is passed, we will not fetch the image-related data from the database. Other non-channel-related query parameters might be from either sources and will be merged together (query parameter has priority.)

The following are some examples of query parameters:

  1. Displaying a greyscale IIIF image with a customized channel name and color:
  2. Displaying a DZI multi-channel image
  3. Changing the watermark and meterScaleInPixels


The viewer app works under a set of assumptions. Most of the assumptions can be configured and modified by using the viewer-config.js file. For more information please refer to configuration document.


Viewer app features are tested manually. For more information, please refer to the Viewer regression tests wiki page.