coco-files.md

title	titleSuffix	author	manager	ms.service	ms.topic	ms.date	ms.author
About COCO files	Azure AI services	PatrickFarley	nitinme	azure-ai-vision	include	02/06/2023	pafarley

About COCO files

COCO files are JSON files with specific required fields: "images", "annotations", and "categories". A sample COCO file will look like this:

{
 "images": [
   {
     "id": 1,
     "width": 500,
     "height": 828,
     "file_name": "0.jpg",
     "absolute_url": "https://blobstorage1.blob.core.windows.net/cpgcontainer/0.jpg"
   },
    {
      "id": 2,
      "width": 754,
      "height": 832,
      "file_name": "1.jpg",
      "absolute_url": "https://blobstorage1.blob.core.windows.net/cpgcontainer/1.jpg"
    },

   ...

  ],
  "annotations": [
    {
      "id": 1,
      "category_id": 7,
      "image_id": 1,
      "area": 0.407,
      "bbox": [
        0.02663142641129032,
        0.40691584277841153,
        0.9524163571731749,
        0.42766634515266866
      ]
    },
    {
      "id": 2,
      "category_id": 9,
      "image_id": 2,
      "area": 0.27,
      "bbox": [
        0.11803319477782331,
        0.41586723392402375,
        0.7765206955096307,
        0.3483334397217212
      ]
    },
    ...

  ],
  "categories": [
    {
      "id": 1,
      "name": "vegall original mixed vegetables"
    },
    {
      "id": 2,
      "name": "Amy's organic soups lentil vegetable"
    },
    {
      "id": 3,
      "name": "Arrowhead 8oz"
    },

    ...

  ]
}

COCO file field reference

If you're generating your own COCO file from scratch, make sure all the required fields are filled with the correct details. The following tables describe each field in a COCO file:

"images"

Key	Type	Description	Required?
id	integer	Unique image ID, starting from 1	Yes
width	integer	Width of the image in pixels	Yes
height	integer	Height of the image in pixels	Yes
file_name	string	A unique name for the image	Yes
absolute_url or coco_url	string	Image path as an absolute URI to a blob in a blob container. The Vision resource must have permission to read the annotation files and all referenced image files.	Yes

The value for absolute_url can be found in your blob container's properties:

"annotations"

Key	Type	Description	Required?
id	integer	ID of the annotation	Yes
category_id	integer	ID of the category defined in the categories section	Yes
image_id	integer	ID of the image	Yes
area	integer	Value of 'Width' x 'Height' (third and fourth values of bbox)	No
bbox	list[float]	Relative coordinates of the bounding box (0 to 1), in the order of 'Left', 'Top', 'Width', 'Height'	Yes

"categories"

Key	Type	Description	Required?
id	integer	Unique ID for each category (label class). These should be present in the annotations section.	Yes
name	string	Name of the category (label class)	Yes

COCO file verification

You can use our Python sample code to check the format of a COCO file.