Detect text in images

This page shows you how to detect image text using the Optical Character Recognition (OCR) API on Google Distributed Cloud (GDC) air-gapped appliance.

The OCR service of Vertex AI on GDC air-gapped appliance detects text in images using the BatchAnnotateImages API method. The service supports JPEG and PNG files for images.

Before you begin

Before you can start using the OCR API, you must have a project with the OCR API enabled and have the appropriate credentials. You can also install client libraries to help you make calls to the API. For more information, see Set up a character recognition project.

Detect text from JPEG and PNG files

The BatchAnnotateImages method detects text from a batch of JPEG or PNG files. You send the file from which you want to detect text directly as content in the API request. The system returns the resulting detected text in JSON format in the API response.

You must specify values for the fields in the JSON body of your API request. The following table contains a description of the request body fields you must provide when you use the BatchAnnotateImages API method for your text detection requests:

Request body fields	Field description
content	The images with text to detect. You provide the Base64 representation (ASCII string) of your binary image data. Note: You can only process images that are stored locally in your GDC air-gapped appliance environment.
type	The type of text detection you need from the image. Specify one of the two annotation features: TEXT_DETECTION detects and extracts text from any image. The JSON response includes the extracted string, individual words, and their bounding boxes. DOCUMENT_TEXT_DETECTION also extracts text from an image, but the service optimizes the response for dense text and documents. The JSON includes page, block, paragraph, word, and break information. For more information about these annotation features, see Optical character recognition features.
language_hints	Optional. List of languages to use for the text detection. The system interprets an empty value for this field as automatic language detection. You don't need to set the language_hints field for languages based on the Latin alphabet. If you know the language of the text in the image, setting a hint improves results. How do language hints work? The language_hints format uses the following BCP 47 language tag formatting guidelines: language ["-" script] ["-" region] *("-" variant) *("-" extension) ["-" privateuse]. For example, the language hint "en-t-i0-handwrit" specifies English language (en), transform extension singleton (t), input method engine transform extension code (i0), and handwriting transform code (handwrit). This roughly says the language is "English transformed from handwriting." You don't need to specify a script code because the "en" language implies Latn. For a list of supported languages, see Supported languages.

Make an API request

Make a request to the OCR pre-trained API using the REST API method. Otherwise, interact with the OCR pre-trained API from a Python script to detect text from JPEG or PNG files.

Note: The BatchAnnotateImages API method only supports a single request per batch call.

The following examples show how to detect text in an image using OCR:

REST

Follow these steps to detect text in images using the REST API method:

1. Save the following request.json file for your request body:

   cat <<- EOF > request.json
   {
     "requests": [
       {
         "image": {
           "content": BASE64_ENCODED_IMAGE
         },
         "features": [
           {
             "type": "FEATURE_TYPE"
           }
         ],
         "image_context": {
           "language_hints": [
             "LANGUAGE_HINT_1",
             "LANGUAGE_HINT_2",
             ...
           ]
         }
       }
     ]
   }
   EOF
   

   Replace the following:

   • BASE64_ENCODED_IMAGE: the Base64 representation (ASCII string) of your binary image data. This string begins with characters that look similar to /9j/4QAYRXhpZgAA...9tAVx/zDQDlGxn//2Q==.
   • FEATURE_TYPE: the type of text detection you need from the image. Allowed values are TEXT_DETECTION or DOCUMENT_TEXT_DETECTION.
   • LANGUAGE_HINT: the BCP 47 language tags to use as language hints for text detection, such as en-t-i0-handwrit. This field is optional and the system interprets an empty value as automatic language detection.

2. Get an authentication token.

3. Make the request:

   curl

   curl -X POST \
     -H "Authorization: Bearer TOKEN" \
     -H "x-goog-user-project: projects/PROJECT_ID" \
     -H "Content-Type: application/json; charset=utf-8" \
     -d @request.json \
     https://ENDPOINT/v1/images:annotate
   

   Replace the following:

   • TOKEN: the authentication token you obtained.
   • PROJECT_ID: your project ID.
   • ENDPOINT: the OCR endpoint that you use for your organization. For more information, view service status and endpoints.

   PowerShell

   $headers = @{
     "Authorization" = "Bearer TOKEN"
     "x-goog-user-project" = "projects/PROJECT_ID"
   }
   
   Invoke-WebRequest
     -Method POST
     -Headers $headers
     -ContentType: "application/json; charset=utf-8"
     -InFile request.json
     -Uri "ENDPOINT/v1/images:annotate" | Select-Object -Expand Content
   

   Replace the following:

   • TOKEN: the authentication token you obtained.
   • ENDPOINT: the OCR endpoint that you use for your organization. For more information, view service status and endpoints.

Python

Follow these steps to use the OCR service from a Python script to detect text in an image:

1. Install the latest version of the OCR client library.

2. Set the required environment variables on a Python script.

3. Authenticate your API request.

4. Add the following code to the Python script you created:

   from google.cloud import vision
   import google.auth
   from google.auth.transport import requests
   from google.api_core.client_options import ClientOptions
   
   audience = "https://ENDPOINT:443"
   api_endpoint="ENDPOINT:443"
   
   def vision_client(creds):
     opts = ClientOptions(api_endpoint=api_endpoint)
     return vision.ImageAnnotatorClient(credentials=creds, client_options=opts)
   
   def main():
     creds = None
     try:
       creds, project_id = google.auth.default()
       creds = creds.with_gdch_audience(audience)
       req = requests.Request()
       creds.refresh(req)
       print("Got token: ")
       print(creds.token)
     except Exception as e:
       print("Caught exception" + str(e))
       raise e
     return creds
   
   def vision_func(creds):
     vc = vision_client(creds)
     image = {"content": "BASE64_ENCODED_IMAGE"}
     features = [{"type_": vision.Feature.Type.FEATURE_TYPE}]
     # Each requests element corresponds to a single image. To annotate more
     # images, create a request element for each image and add it to
     # the array of requests
     req = {"image": image, "features": features}
   
     metadata = [("x-goog-user-project", "projects/PROJECT_ID")]
   
     resp = vc.annotate_image(req,metadata=metadata)
   
     print(resp)
   
   if __name__=="__main__":
     creds = main()
     vision_func(creds)
   

   Replace the following:

   • ENDPOINT: the OCR endpoint that you use for your organization. For more information, view service status and endpoints.
   • BASE64_ENCODED_IMAGE: the Base64 representation (ASCII string) of your binary image data. This string begins with characters that look similar to /9j/4QAYRXhpZgAA...9tAVx/zDQDlGxn//2Q==.
   • FEATURE_TYPE: the type of text detection you need from the image. Allowed values are TEXT_DETECTION or DOCUMENT_TEXT_DETECTION.
   • PROJECT_ID: your project ID.

5. Save the Python script.

6. Run the Python script to detect text in the image:

   python SCRIPT_NAME
   

   Replace SCRIPT_NAME with the name you gave to your Python script, such as vision.py.