# Annotation

## Annotation

An image is composed of array of pixels, and we have two ways to annotate on the pixels, by using the `segmentation` tool (as RLE - run-length encoding) and `vector` tool.

### Segmentation (RLE)

RLE (run-length encoding) object is used only when the label type is `segmentation`, and each label contains only one RLE object. When annotating with RLE, we basically annotate the pixel in the image:

<div align="center"><img src="/files/-MFsr9461RvMil0h3916" alt=""></div>

An RLE object is represented as:

```
{
  "type": STRING,
  "segmentation": [
    [x, y, length from x to right],
    ...
  ]
}
```

* **type**: Type of the segmentation, which currently supports `rle` only.
* **segmentation**: Two-dimensional array for RLE.
  * The minimal unit of segmentation is a 1x1 pixel area, which is an integer.
  * For example, given by the 4x4 pixel image below with annotation, the array will be:

```
{
  "segmentation": [
    [2, 0, 2],
    [0, 1, 3],
    [2, 2, 1]
  ]
}
```

&#x20;

![](/files/-MFss-VXeB89_z9uMQZ8)

### vector

A vector object is used only when the label type is `vector`, and each label can contain multiple vector objects. When annotating with vector, we basically describe the coordinates of the annotation in the image:

![](/files/-MFssAMnbdv3fbUGJ8aU)

A vector object is represented as:

```
{
  "type": STRING,
  "attributes": [
    {
      "name": STRING,
      "values": [STRING]
    }
  ],
  "segmentation": [x1, y1, x2, y2, ..., xn, yn]
}
```

* **type**: Type of the vector object, currently supports `polygon`, `boundingBox`, `path` and `point`.
* **attributes**: Custom attributes to describe the vector object.
  * **name**: Name of the attribute.
  * **values**: Array of value to the attribute.
* **segmentation**: Array of coordinate which represents the vector object.

  * The minimal unit of segmentation is a coordinate, which is float.
  * if the segmentation type is `polygon`, the value will be `[x1, y1, x2, y2, ..., xn, yn]`.
  * if the segmentation type is `boundingBox`, the value will be `[x1, y1, x2, y2, x3, y3, x4, y4]`.
  * if the segmentation type is `path`, the value will be `[x1, y1, x2, y2, ..., xn, yn]`.
  * if the segmentation type is `point`, the value will be `[x1, y1]`.
  * The coordinates can be either clockwise or counterclockwise as long as it follows the order.
  * For example, given by the 4x4 pixel images below with annotation, the array will be:

  &#x20;

![](/files/-MGDBUPUkflLwNWZ1I8s)

![](/files/-MGDBbMWY4SxSnuhK_YC)


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