Image captions

imagetext is the name of the model that supports image captioning. imagetext generates a caption from an image you provide based on the language that you specify. The model supports the following languages: English (en), German (de), French (fr), Spanish (es) and Italian (it).

To explore this model in the console, see the Image Captioning model card in the Model Garden.

View Imagen for Captioning & VQA model card

Use cases

Some common use cases for image captioning include:

  • Creators can generate captions for uploaded images and videos (for example, a short description of a video sequence)
  • Generate captions to describe products
  • Integrate captioning with an app using the API to create new experiences

HTTP request

POST https://us-central1-aiplatform.googleapis.com/v1/projects/PROJECT_ID/locations/us-central1/publishers/google/models/imagetext:predict

Request body

{
  "instances": [
    {
      "image": {
        // Union field can be only one of the following:
        "bytesBase64Encoded": string,
        "gcsUri": string,
        // End of list of possible types for union field.
        "mimeType": string
      }
    }
  ],
  "parameters": {
    "sampleCount": integer,
    "storageUri": string,
    "language": string,
    "seed": integer
  }
}

Use the following parameters for the Imagen model imagetext. For more information, see Get image descriptions using visual captioning.

Parameter Description Acceptable values
instances An array that contains the object with image details to get information about. array (1 image object allowed)
bytesBase64Encoded The image to caption. Base64-encoded image string (PNG or JPEG, 20 MB max)
gcsUri The Cloud Storage URI of the image to caption. string URI of the image file in Cloud Storage (PNG or JPEG, 20 MB max)
mimeType Optional. The MIME type of the image you specify. string (image/jpeg or image/png)
sampleCount Number of generated text strings. Int value: 1-3
seed Optional. The seed for random number generator (RNG). If RNG seed is the same for requests with the inputs, the prediction results will be the same. integer
storageUri Optional. The Cloud Storage location to save the generated text responses. string
language Optional. The text prompt for guiding the response. string: en (default), de, fr, it, es

Sample request

REST

To test a text prompt by using the Vertex AI API, send a POST request to the publisher model endpoint.

Before using any of the request data, make the following replacements:

  • PROJECT_ID: Your Google Cloud project ID.
  • LOCATION: Your project's region. For example, us-central1, europe-west2, or asia-northeast3. For a list of available regions, see Generative AI on Vertex AI locations.
  • B64_IMAGE: The image to get captions for. The image must be specified as a base64-encoded byte string. Size limit: 10 MB.
  • RESPONSE_COUNT: The number of image captions you want to generate. Accepted integer values: 1-3.
  • LANGUAGE_CODE: One of the supported language codes. Languages supported:
    • English (en)
    • French (fr)
    • German (de)
    • Italian (it)
    • Spanish (es)

HTTP method and URL: 

POST https://LOCATION-aiplatform.googleapis.com/v1/projects/PROJECT_ID/locations/LOCATION/publishers/google/models/imagetext:predict

Request JSON body: 

{
  "instances": [
    {
      "image": {
          "bytesBase64Encoded": "B64_IMAGE"
      }
    }
  ],
  "parameters": {
    "sampleCount": RESPONSE_COUNT,
    "language": "LANGUAGE_CODE"
  }
}

To send your request, choose one of these options:

curl

Save the request body in a file named request.json, and execute the following command: 

curl -X POST \
     -H "Authorization: Bearer $(gcloud auth print-access-token)" \
     -H "Content-Type: application/json; charset=utf-8" \
     -d @request.json \
     "https://LOCATION-aiplatform.googleapis.com/v1/projects/PROJECT_ID/locations/LOCATION/publishers/google/models/imagetext:predict"

PowerShell

Save the request body in a file named request.json, and execute the following command: 

$cred = gcloud auth print-access-token
$headers = @{ "Authorization" = "Bearer $cred" }

Invoke-WebRequest `
    -Method POST `
    -Headers $headers `
    -ContentType: "application/json; charset=utf-8" `
    -InFile request.json `
    -Uri "https://LOCATION-aiplatform.googleapis.com/v1/projects/PROJECT_ID/locations/LOCATION/publishers/google/models/imagetext:predict" | Select-Object -Expand Content
The following sample responses are for a request with "sampleCount": 2. The response returns two prediction strings.

English (en):

{
  "predictions": [
    "a yellow mug with a sheep on it sits next to a slice of cake",
    "a cup of coffee with a heart shaped latte art next to a slice of cake"
  ],
  "deployedModelId": "DEPLOYED_MODEL_ID",
  "model": "projects/PROJECT_ID/locations/LOCATION/models/MODEL_ID",
  "modelDisplayName": "MODEL_DISPLAYNAME",
  "modelVersionId": "1"
}

Spanish (es):

{
  "predictions": [
    "una taza de café junto a un plato de pastel de chocolate",
    "una taza de café con una forma de corazón en la espuma"
  ]
}

Response body

{
  "predictions": [ string ]
}
Response element Description
predictions List of text strings representing captions, sorted by confidence.

Sample response

{
  "predictions": [
    "text1",
    "text2"
  ]
}