Image with area selection

Note. This section describes how to add an area selection editor to an image using the HTML/JS/CSS tools. You can also try creating an area selection editor in Template Builder.

The editor lets you select an area of the image using either a rectangle or an arbitrary polygon:

Note. Don't add training or control tasks in the project that features image area selection editor.

Adding the editor

If you need to add an image editor without selected objects:

  1. Connect the $TOLOKA_ASSETS/js/image-annotation.js library (click in the Task interface block on the project page).

  2. Include the {{field type="image-annotation" name="<output field name>" src=<image URL>}} component in the HTML code of the interface. Example:

    {{field type="image-annotation" name="result" src=image}}
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    For a complete list of parameters, see the table.

  3. Add a field for entering an image link in the input data.
  4. Add the result field with the json type in the output data.

The result field will be used for a JSON object with the point coordinates. Example:

[{"data":{"p1":{"x":0.472,"y":0.413},"p2":{"x":0.932,"y":0.877}},"type":"rectangle"},
{"data":[{"x":0.143,"y":0.807},{"x":0.317,"y":0.87},{"x":0.511,"y":0.145},{"x":0.328,"y":0.096},{"x":0.096,"y":0.554}],"type":"polygon"}] 

The x and y values are numbers from 0 to 1. Length and width of the image are taken as 1, with the center of coordinates in the upper-left corner of the image.

Parameters

Parameter

Overview

Required

Default value

type
Field type: image-annotation, the image area selection editor.

yes

no

name

Attribute for the output data field. Contains the output field name.

yes

no

src

Image URL. Supported values:

  • URL from the task input data. For example, from the field with the url: src=image ID.

  • Direct link. The HTTPS protocol is recommended. For example, src="https://mywebsite.ru/img1.png".

  • Relative link.

yes

no

annotations

Attribute for the input data field. Contains the input data field name. Here you can provide the selection coordinates for further editing. The data format is a JSON object.

no

no

Parameter

Overview

Required

Default value

type
Field type: image-annotation, the image area selection editor.

yes

no

name

Attribute for the output data field. Contains the output field name.

yes

no

src

Image URL. Supported values:

  • URL from the task input data. For example, from the field with the url: src=image ID.

  • Direct link. The HTTPS protocol is recommended. For example, src="https://mywebsite.ru/img1.png".

  • Relative link.

yes

no

annotations

Attribute for the input data field. Contains the input data field name. Here you can provide the selection coordinates for further editing. The data format is a JSON object.

no

no

Shortcuts

By default, you can use the following keyboard shortcuts in the task:
  • C closes a polygon connecting the first and last points with a line.
  • D deletes the selected point, selected object, or last point when creating a polygon.
  • Arrows move the selected point. With Alt pressed, they move it slower. With Alt+Shift pressed, they move it faster.
  • Tab moves from the selected point to the next one.
  • Shift+Tab moves from the selected point to the previous one.

Tell performers about keyboard shortcuts in the instructions to speed up task completion.

Selection tools

By default, the polygon tool is added to the task interface.

You can change the tool set:

To add a rectangle, delete the CSS selector:
.image-annotation-editor__shape-rectangle {
  display: none;
}
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Annotation

To use annotations, insert one of these examples into the JS block:

exports.Task = extend(TolokaHandlebarsTask, function (options) {
    TolokaHandlebarsTask.call(this, options);
}, {
    onRender: function() {
        var field = this.getField('result');
        var editor = field.getEditor();
        editor.annotationInterface = field.createAnnotationInterface({
            createInterfaceElement: function() {
                this._input = document.createElement('input');
                this._input.addEventListener('input', function() {
                    this._shape.annotation = this._input.value;
                }.bind(this));
                return this._input;
            },
            onShow: function(shape) {
                this._shape = shape;
                this._input.value = shape.annotation;
            }
        });
   },
  onDestroy: function() {
    // Task is completed. Global resources can be released (if used)
  }
});

function extend(ParentClass, constructorFunction, prototypeHash) {
  constructorFunction = constructorFunction || function () {};
  prototypeHash = prototypeHash || {};
  if (ParentClass) {
    constructorFunction.prototype = Object.create(ParentClass.prototype);
  }
  for (var i in prototypeHash) {
    constructorFunction.prototype[i] = prototypeHash[i];
  }
  return constructorFunction;
}
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Explanation of examples

To let the performer add an annotation to the selected area or select it from the list, you need to add an interface element to the task (for example, a text field or a drop-down list):

  1. Get the object of the getEditor() editor and the getField('result') annotation interface in the onRender() method:

    var field = this.getField('result');    
    var editor = field.getEditor();
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  2. Set the annotation interface implementation in methods:
    • createInterfaceElement() — Calls the DOM element of the interface (called once during initialization).

    • onShow(shape, options) — Shows the annotation interface when the performer hovers the mouse over the selected area. Gets JSON with the coordinates of the polygon points as input. In this JSON, you can write the annotation that the performer entered.

Performer interactions with the editor cause the following events:

  • shape:start — Starts area selection.

  • shape:finish — Completes area selection.

  • shape:cancel — Deletes a point.

  • shape:remove — Deletes the selection.

To subscribe to these events:

editor.on('shape:start', function() {
/* event handling */
});
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