Script Parameters

Revision as of 11:20, 20 April 2016 by Rueden (talk | contribs) (Parameter properties)

All scripting languages have access to a universal @parameter notation for declaring inputs and outputs. This approach is preferred to using ImageJ 1.x GenericDialog because it is totally agnostic of the user interface, allowing such scripts to run in a variety of contexts. As with ImageJ2 plugins, script parameterization is based on the SciJava @Parameter annotation - so experience with plugin writing directly translates to scripting, and vice versa.


Basic syntax

The rules for @parameter use are as follows:

  1. All parameter declarations must appear in comments. Each comment line contains a single parameter declaration and nothing else.
  2. Any parameters after the first non-parameter line will not be recognized.
  3. @type variableName will declare an input of the indicated type, assigned to the specified name.
  4. @OUTPUT type outputName will declare the variable of the specified name as an output parameter with the given type.

For example, if we look at the template supplied with Fiji:

# @String name
# @OUTPUT String greeting

# A Jython script with parameters.
# It is the duty of the scripting framework to harvest
# the 'name' parameter from the user, and then display
# the 'greeting' output parameter, based on its type.

greeting = "Hello, " + name + "!"

We see that an input parameter name of type String is declared. @arameters are handled automatically by the framework; if we run this script when the User Interface is available (e.g. from the script editor), the name parameter will automatically be harvested via a pop-up dialog:


We could also run this script headlessly, thanks to the general nature of @parameters.

When the script is completed, any @OUTPUT variables are handled by the framework, based on their type. In this case we expect the greeting variable to be printed, since it is a string.

Parameter types

A list of possible data types and the corresponding widgets is provided:

Data type Widget type
Boolean checkbox
short | int | long numeric field
Short | Integer | Long numeric field
BigDecimal numeric field
Character | String text field
ImagePlus (>=2 images) triggers a dropdown list
ColorRGB color chooser
Date date chooser
File file chooser (opener)

By implementing InputWidget it is possible to extend this list.

Parameter properties

If you look at the @Parameter annotation, you will notice it has many properties—for example, name and description.

Script parameters can set these properties, following these guidelines:

  1. All properties are defined in a single parenthetical expression immediately following the @Type declaration.
  2. Properties are set by a comma-separated list of key=value pairs

Properties are your way to customize how an @parameter should be handled by the framework.

Widget labels

Widgets are the User Interface elements shown to users to collect input information. For example, instead of just displaying "Name" to the user, we can add a custom label to the field of our script as follows:

# @String(label="Please enter your name") name
# @OUTPUT String greeting

greeting = "Hello, " + name + "!"

Widget mouseover

We can add a description property to provide mouse-over text for our field:

# @String(label="Please enter your name", description="Your name") name
# @OUTPUT String greeting

greeting = "Hello, " + name + "!"

Default values

Default values are also supported as parameter properties:

# @Integer(label="An integer!",value=15) someInt

Files and Folders

By default, a `@File` parameter will create a chooser for a single file:

# @File(label="Select a file") myFile


If you want to select a directory instead, use a style property:

# @File(label="Select a directory", style="directory") myDir