Optical Character Recognition (OCR) Tutorial

Learn how to perform optical character recognition (OCR) on Google Cloud Platform. This tutorial demonstrates how to upload image files to Google Cloud Storage, extract text from the images using the Google Cloud Vision API, translate the text using the Google Cloud Translation API, and save your translations back to Cloud Storage. Google Cloud Pub/Sub is used to queue various tasks and trigger the right Cloud Functions to carry them out.

Objectives

  • Write and deploy several Background Cloud Functions.
  • Upload images to Cloud Storage.
  • Extract, translate and save text contained in uploaded images.

Costs

This tutorial uses billable components of Cloud Platform, including:

  • Google Cloud Functions
  • Google Cloud Pub/Sub
  • Google Cloud Storage
  • Google Cloud Translation API
  • Google Cloud Vision API

Use the Pricing Calculator to generate a cost estimate based on your projected usage.

New Cloud Platform users might be eligible for a free trial.

Before you begin

  1. Sign in to your Google Account.

    If you don't already have one, sign up for a new account.

  2. In the Cloud Console, on the project selector page, select or create a Cloud project.

    Go to the project selector page

  3. Make sure that billing is enabled for your Google Cloud project. Learn how to confirm billing is enabled for your project.

  4. Enable the Cloud Functions, Cloud Pub/Sub, Cloud Storage, Cloud Translation, and Cloud Vision APIs.

    Enable the APIs

  5. Update gcloud components:
    gcloud components update
  6. Prepare your development environment.

Visualizing the flow of data

The flow of data in the OCR tutorial application involves several steps:

  1. An image that contains text in any language is uploaded to Cloud Storage.
  2. A Cloud Function is triggered, which uses the Vision API to extract the text and detect the source language.
  3. The text is queued for translation by publishing a message to a Pub/Sub topic. A translation is queued for each target language different from the source language.
  4. If a target language matches the source language, the translation queue is skipped, and text is sent to the result queue, another Pub/Sub topic.
  5. A Cloud Function uses the Translation API to translate the text in the translation queue. The translated result is sent to the result queue.
  6. Another Cloud Function saves the translated text from the result queue to Cloud Storage.
  7. The results are found in Cloud Storage as txt files for each translation.

It may help to visualize the steps:

Preparing the application

  1. Create a Cloud Storage bucket to upload images to, where YOUR_IMAGE_BUCKET_NAME is a globally unique bucket name:

    gsutil mb gs://YOUR_IMAGE_BUCKET_NAME
    
  2. Create a Cloud Storage bucket to save text translations to, where YOUR_RESULT_BUCKET_NAME is a globally unique bucket name:

    gsutil mb gs://YOUR_RESULT_BUCKET_NAME
    
  3. Create a Cloud Pub/Sub topic to publish translation requests to, where YOUR_TRANSLATE_TOPIC_NAME is the name of your translation request topic:

    gcloud pubsub topics create gs://YOUR_TRANSLATE_TOPIC_NAME
    
  4. Create a Cloud Pub/Sub topic to publish finished translation results to, where YOUR_RESULT_TOPIC_NAME is the name of your translation result topic:

    gcloud pubsub topics create gs://YOUR_RESULT_TOPIC_NAME
    
  5. Clone the sample app repository to your local machine:

    Node.js

    git clone https://github.com/GoogleCloudPlatform/nodejs-docs-samples.git

    Alternatively, you can download the sample as a zip file and extract it.

    Python

    git clone https://github.com/GoogleCloudPlatform/python-docs-samples.git

    Alternatively, you can download the sample as a zip file and extract it.

    Go

    git clone https://github.com/GoogleCloudPlatform/golang-samples.git

    Alternatively, you can download the sample as a zip file and extract it.

    Java

    git clone https://github.com/GoogleCloudPlatform/java-docs-samples.git

    Alternatively, you can download the sample as a zip file and extract it.

  6. Change to the directory that contains the Cloud Functions sample code:

    Node.js

    cd nodejs-docs-samples/functions/ocr/app/

    Python

    cd python-docs-samples/functions/ocr/app/

    Go

    cd golang-samples/functions/ocr/app/

    Java

    cd java-docs-samples/functions/ocr/ocr-process-image/

Understanding the code

Importing dependencies

The application must import several dependencies in order to communicate with Google Cloud Platform services:

Node.js

// Get a reference to the Pub/Sub component
const {PubSub} = require('@google-cloud/pubsub');
const pubsub = new PubSub();
// Get a reference to the Cloud Storage component
const {Storage} = require('@google-cloud/storage');
const storage = new Storage();

// Get a reference to the Cloud Vision API component
const Vision = require('@google-cloud/vision');
const vision = new Vision.ImageAnnotatorClient();

// Get a reference to the Translate API component
const {Translate} = require('@google-cloud/translate').v2;
const translate = new Translate();

Python

import base64
import json
import os

from google.cloud import pubsub_v1
from google.cloud import storage
from google.cloud import translate_v2 as translate
from google.cloud import vision

vision_client = vision.ImageAnnotatorClient()
translate_client = translate.Client()
publisher = pubsub_v1.PublisherClient()
storage_client = storage.Client()

project_id = os.environ['GCP_PROJECT']

Go


// Package ocr contains Go samples for creating OCR
// (Optical Character Recognition) Cloud functions.
package ocr

import (
	"context"
	"fmt"
	"os"
	"strings"
	"time"

	"cloud.google.com/go/pubsub"
	"cloud.google.com/go/storage"
	"cloud.google.com/go/translate"
	vision "cloud.google.com/go/vision/apiv1"
	"golang.org/x/text/language"
)

type ocrMessage struct {
	Text     string       `json:"text"`
	FileName string       `json:"fileName"`
	Lang     language.Tag `json:"lang"`
	SrcLang  language.Tag `json:"srcLang"`
}

// GCSEvent is the payload of a GCS event.
type GCSEvent struct {
	Bucket         string    `json:"bucket"`
	Name           string    `json:"name"`
	Metageneration string    `json:"metageneration"`
	ResourceState  string    `json:"resourceState"`
	TimeCreated    time.Time `json:"timeCreated"`
	Updated        time.Time `json:"updated"`
}

// PubSubMessage is the payload of a Pub/Sub event.
type PubSubMessage struct {
	Data []byte `json:"data"`
}

var (
	visionClient    *vision.ImageAnnotatorClient
	translateClient *translate.Client
	pubsubClient    *pubsub.Client
	storageClient   *storage.Client

	projectID      string
	resultBucket   string
	resultTopic    string
	toLang         []string
	translateTopic string
)

func setup(ctx context.Context) error {
	projectID = os.Getenv("GOOGLE_CLOUD_PROJECT")
	resultBucket = os.Getenv("RESULT_BUCKET")
	resultTopic = os.Getenv("RESULT_TOPIC")
	toLang = strings.Split(os.Getenv("TO_LANG"), ",")
	translateTopic = os.Getenv("TRANSLATE_TOPIC")

	var err error // Prevent shadowing clients with :=.

	if visionClient == nil {
		visionClient, err = vision.NewImageAnnotatorClient(ctx)
		if err != nil {
			return fmt.Errorf("vision.NewImageAnnotatorClient: %v", err)
		}
	}

	if translateClient == nil {
		translateClient, err = translate.NewClient(ctx)
		if err != nil {
			return fmt.Errorf("translate.NewClient: %v", err)
		}
	}

	if pubsubClient == nil {
		pubsubClient, err = pubsub.NewClient(ctx, projectID)
		if err != nil {
			return fmt.Errorf("translate.NewClient: %v", err)
		}
	}

	if storageClient == nil {
		storageClient, err = storage.NewClient(ctx)
		if err != nil {
			return fmt.Errorf("storage.NewClient: %v", err)
		}
	}
	return nil
}

Java

public class OcrProcessImage implements BackgroundFunction<GcsEvent> {
  // TODO<developer> set these environment variables
  private static final String PROJECT_ID = System.getenv("GCP_PROJECT");
  private static final String TRANSLATE_TOPIC_NAME = System.getenv("TRANSLATE_TOPIC");
  private static final String[] TO_LANGS = System.getenv("TO_LANG").split(",");

  private static final Logger logger = Logger.getLogger(OcrProcessImage.class.getName());
  private static final String LOCATION_NAME = LocationName.of(PROJECT_ID, "global").toString();
  private Publisher publisher;

  public OcrProcessImage() throws IOException {
    publisher = Publisher.newBuilder(
        ProjectTopicName.of(PROJECT_ID, TRANSLATE_TOPIC_NAME)).build();
  }
}

Processing images

The following function reads an uploaded image file from Cloud Storage and calls a function to detect whether the image contains text:

Node.js

/**
 * This function is exported by index.js, and is executed when
 * a file is uploaded to the Cloud Storage bucket you created
 * for uploading images.
 *
 * @param {object} event A Google Cloud Storage File object.
 */
exports.processImage = async (event) => {
  const {bucket, name} = event;

  if (!bucket) {
    throw new Error(
      'Bucket not provided. Make sure you have a "bucket" property in your request'
    );
  }
  if (!name) {
    throw new Error(
      'Filename not provided. Make sure you have a "name" property in your request'
    );
  }

  await detectText(bucket, name);
  console.log(`File ${name} processed.`);
};

Python

def process_image(file, context):
    """Cloud Function triggered by Cloud Storage when a file is changed.
    Args:
        file (dict): Metadata of the changed file, provided by the triggering
                                 Cloud Storage event.
        context (google.cloud.functions.Context): Metadata of triggering event.
    Returns:
        None; the output is written to stdout and Stackdriver Logging
    """
    bucket = validate_message(file, 'bucket')
    name = validate_message(file, 'name')

    detect_text(bucket, name)

    print('File {} processed.'.format(file['name']))

Go


package ocr

import (
	"context"
	"fmt"
	"log"
)

// ProcessImage is executed when a file is uploaded to the Cloud Storage bucket you
// created for uploading images. It runs detectText, which processes the image for text.
func ProcessImage(ctx context.Context, event GCSEvent) error {
	if err := setup(ctx); err != nil {
		return fmt.Errorf("ProcessImage: %v", err)
	}
	if event.Bucket == "" {
		return fmt.Errorf("empty file.Bucket")
	}
	if event.Name == "" {
		return fmt.Errorf("empty file.Name")
	}
	if err := detectText(ctx, event.Bucket, event.Name); err != nil {
		return fmt.Errorf("detectText: %v", err)
	}
	log.Printf("File %s processed.", event.Name)
	return nil
}

Java


import com.google.cloud.functions.BackgroundFunction;
import com.google.cloud.functions.Context;
import com.google.cloud.pubsub.v1.Publisher;
import com.google.cloud.translate.v3.DetectLanguageRequest;
import com.google.cloud.translate.v3.DetectLanguageResponse;
import com.google.cloud.translate.v3.LocationName;
import com.google.cloud.translate.v3.TranslationServiceClient;
import com.google.cloud.vision.v1.AnnotateImageRequest;
import com.google.cloud.vision.v1.AnnotateImageResponse;
import com.google.cloud.vision.v1.Feature;
import com.google.cloud.vision.v1.Image;
import com.google.cloud.vision.v1.ImageAnnotatorClient;
import com.google.cloud.vision.v1.ImageSource;
import com.google.protobuf.ByteString;
import com.google.pubsub.v1.ProjectTopicName;
import com.google.pubsub.v1.PubsubMessage;
import functions.eventpojos.GcsEvent;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.logging.Level;
import java.util.logging.Logger;

  @Override
  public void accept(GcsEvent gcsEvent, Context context) {

    // Validate parameters
    String bucket = gcsEvent.getBucket();
    if (bucket == null) {
      throw new IllegalArgumentException("Missing bucket parameter");
    }
    String filename = gcsEvent.getName();
    if (filename == null) {
      throw new IllegalArgumentException("Missing name parameter");
    }

    detectText(bucket, filename);
  }
}

The following function extracts text from the image using the Cloud Vision API and queues the text for translation:

Node.js

/**
 * Detects the text in an image using the Google Vision API.
 *
 * @param {string} bucketName Cloud Storage bucket name.
 * @param {string} filename Cloud Storage file name.
 * @returns {Promise}
 */
const detectText = async (bucketName, filename) => {
  console.log(`Looking for text in image ${filename}`);
  const [textDetections] = await vision.textDetection(
    `gs://${bucketName}/${filename}`
  );
  const [annotation] = textDetections.textAnnotations;
  const text = annotation ? annotation.description : '';
  console.log(`Extracted text from image:`, text);

  let [translateDetection] = await translate.detect(text);
  if (Array.isArray(translateDetection)) {
    [translateDetection] = translateDetection;
  }
  console.log(
    `Detected language "${translateDetection.language}" for ${filename}`
  );

  // Submit a message to the bus for each language we're going to translate to
  const TO_LANGS = process.env.TO_LANG.split(',');
  const topicName = process.env.TRANSLATE_TOPIC;

  const tasks = TO_LANGS.map((lang) => {
    const messageData = {
      text: text,
      filename: filename,
      lang: lang,
    };

    return publishResult(topicName, messageData);
  });

  return Promise.all(tasks);
};

Python

def detect_text(bucket, filename):
    print('Looking for text in image {}'.format(filename))

    futures = []

    text_detection_response = vision_client.text_detection({
        'source': {'image_uri': 'gs://{}/{}'.format(bucket, filename)}
    })
    annotations = text_detection_response.text_annotations
    if len(annotations) > 0:
        text = annotations[0].description
    else:
        text = ''
    print('Extracted text {} from image ({} chars).'.format(text, len(text)))

    detect_language_response = translate_client.detect_language(text)
    src_lang = detect_language_response['language']
    print('Detected language {} for text {}.'.format(src_lang, text))

    # Submit a message to the bus for each target language
    to_langs = os.environ['TO_LANG'].split(',')
    for target_lang in to_langs:
        topic_name = os.environ['TRANSLATE_TOPIC']
        if src_lang == target_lang or src_lang == 'und':
            topic_name = os.environ['RESULT_TOPIC']
        message = {
            'text': text,
            'filename': filename,
            'lang': target_lang,
            'src_lang': src_lang
        }
        message_data = json.dumps(message).encode('utf-8')
        topic_path = publisher.topic_path(project_id, topic_name)
        future = publisher.publish(topic_path, data=message_data)
        futures.append(future)
    for future in futures:
        future.result()

Go


package ocr

import (
	"context"
	"encoding/json"
	"fmt"
	"log"

	"cloud.google.com/go/pubsub"
	"golang.org/x/text/language"
	visionpb "google.golang.org/genproto/googleapis/cloud/vision/v1"
)

// detectText detects the text in an image using the Google Vision API.
func detectText(ctx context.Context, bucketName, fileName string) error {
	log.Printf("Looking for text in image %v", fileName)
	maxResults := 1
	image := &visionpb.Image{
		Source: &visionpb.ImageSource{
			GcsImageUri: fmt.Sprintf("gs://%s/%s", bucketName, fileName),
		},
	}
	annotations, err := visionClient.DetectTexts(ctx, image, &visionpb.ImageContext{}, maxResults)
	if err != nil {
		return fmt.Errorf("DetectTexts: %v", err)
	}
	text := ""
	if len(annotations) > 0 {
		text = annotations[0].Description
	}
	if len(annotations) == 0 || len(text) == 0 {
		log.Printf("No text detected in image %q. Returning early.", fileName)
		return nil
	}
	log.Printf("Extracted text %q from image (%d chars).", text, len(text))

	detectResponse, err := translateClient.DetectLanguage(ctx, []string{text})
	if err != nil {
		return fmt.Errorf("DetectLanguage: %v", err)
	}
	if len(detectResponse) == 0 || len(detectResponse[0]) == 0 {
		return fmt.Errorf("DetectLanguage gave empty response")
	}
	srcLang := detectResponse[0][0].Language.String()
	log.Printf("Detected language %q for text %q.", srcLang, text)

	// Submit a message to the bus for each target language
	for _, targetLang := range toLang {
		topicName := translateTopic
		if srcLang == targetLang || srcLang == "und" { // detection returns "und" for undefined language
			topicName = resultTopic
		}
		targetTag, err := language.Parse(targetLang)
		if err != nil {
			return fmt.Errorf("language.Parse: %v", err)
		}
		srcTag, err := language.Parse(srcLang)
		if err != nil {
			return fmt.Errorf("language.Parse: %v", err)
		}
		message, err := json.Marshal(ocrMessage{
			Text:     text,
			FileName: fileName,
			Lang:     targetTag,
			SrcLang:  srcTag,
		})
		if err != nil {
			return fmt.Errorf("json.Marshal: %v", err)
		}
		topic := pubsubClient.Topic(topicName)
		ok, err := topic.Exists(ctx)
		if err != nil {
			return fmt.Errorf("Exists: %v", err)
		}
		if !ok {
			topic, err = pubsubClient.CreateTopic(ctx, topicName)
			if err != nil {
				return fmt.Errorf("CreateTopic: %v", err)
			}
		}
		msg := &pubsub.Message{
			Data: []byte(message),
		}
		if _, err = topic.Publish(ctx, msg).Get(ctx); err != nil {
			return fmt.Errorf("Get: %v", err)
		}
	}
	return nil
}

Java

private void detectText(String bucket, String filename) {
  logger.info("Looking for text in image " + filename);

  List<AnnotateImageRequest> visionRequests = new ArrayList<>();
  String gcsPath = String.format("gs://%s/%s", bucket, filename);

  ImageSource imgSource = ImageSource.newBuilder().setGcsImageUri(gcsPath).build();
  Image img = Image.newBuilder().setSource(imgSource).build();

  Feature textFeature = Feature.newBuilder().setType(Feature.Type.TEXT_DETECTION).build();
  AnnotateImageRequest visionRequest =
      AnnotateImageRequest.newBuilder().addFeatures(textFeature).setImage(img).build();
  visionRequests.add(visionRequest);

  // Detect text in an image using the Cloud Vision API
  AnnotateImageResponse visionResponse;
  try (ImageAnnotatorClient client = ImageAnnotatorClient.create()) {
    visionResponse = client.batchAnnotateImages(visionRequests).getResponses(0);
    if (visionResponse == null || !visionResponse.hasFullTextAnnotation()) {
      logger.info(String.format("Image %s contains no text", filename));
      return;
    }

    if (visionResponse.hasError()) {
      // Log error
      logger.log(
          Level.SEVERE, "Error in vision API call: " + visionResponse.getError().getMessage());
      return;
    }
  } catch (IOException e) {
    // Log error (since IOException cannot be thrown by a Cloud Function)
    logger.log(Level.SEVERE, "Error detecting text: " + e.getMessage(), e);
    return;
  }

  String text = visionResponse.getFullTextAnnotation().getText();
  logger.info("Extracted text from image: " + text);

  // Detect language using the Cloud Translation API
  DetectLanguageRequest languageRequest =
      DetectLanguageRequest.newBuilder()
          .setParent(LOCATION_NAME)
          .setMimeType("text/plain")
          .setContent(text)
          .build();
  DetectLanguageResponse languageResponse;
  try (TranslationServiceClient client = TranslationServiceClient.create()) {
    languageResponse = client.detectLanguage(languageRequest);
  } catch (IOException e) {
    // Log error (since IOException cannot be thrown by a function)
    logger.log(Level.SEVERE, "Error detecting language: " + e.getMessage(), e);
    return;
  }

  if (languageResponse.getLanguagesCount() == 0) {
    logger.info("No languages were detected for text: " + text);
    return;
  }

  String languageCode = languageResponse.getLanguages(0).getLanguageCode();
  logger.info(String.format("Detected language %s for file %s", languageCode, filename));

  // Send a Pub/Sub translation request for every language we're going to translate to
  for (String targetLanguage : TO_LANGS) {
    logger.info("Sending translation request for language " + targetLanguage);
    OcrTranslateApiMessage message = new OcrTranslateApiMessage(text, filename, targetLanguage);
    ByteString byteStr = ByteString.copyFrom(message.toPubsubData());
    PubsubMessage pubsubApiMessage = PubsubMessage.newBuilder().setData(byteStr).build();
    try {
      publisher.publish(pubsubApiMessage).get();
    } catch (InterruptedException | ExecutionException e) {
      // Log error
      logger.log(Level.SEVERE, "Error publishing translation request: " + e.getMessage(), e);
      return;
    }
  }
}

Translating text

The following function translates the extracted text and queues the translated text to be saved back to Cloud Storage:

Node.js

/**
 * This function is exported by index.js, and is executed when
 * a message is published to the Cloud Pub/Sub topic specified
 * by the TRANSLATE_TOPIC environment variable. The function
 * translates text using the Google Translate API.
 *
 * @param {object} event The Cloud Pub/Sub Message object.
 * @param {string} {messageObject}.data The "data" property of the Cloud Pub/Sub
 * Message. This property will be a base64-encoded string that you must decode.
 */
exports.translateText = async (event) => {
  const pubsubData = event.data;
  const jsonStr = Buffer.from(pubsubData, 'base64').toString();
  const {text, filename, lang} = JSON.parse(jsonStr);

  if (!text) {
    throw new Error(
      'Text not provided. Make sure you have a "text" property in your request'
    );
  }
  if (!filename) {
    throw new Error(
      'Filename not provided. Make sure you have a "filename" property in your request'
    );
  }
  if (!lang) {
    throw new Error(
      'Language not provided. Make sure you have a "lang" property in your request'
    );
  }

  console.log(`Translating text into ${lang}`);
  const [translation] = await translate.translate(text, lang);

  console.log(`Translated text:`, translation);

  const messageData = {
    text: translation,
    filename: filename,
    lang: lang,
  };

  await publishResult(process.env.RESULT_TOPIC, messageData);
  console.log(`Text translated to ${lang}`);
};

Python

def translate_text(event, context):
    if event.get('data'):
        message_data = base64.b64decode(event['data']).decode('utf-8')
        message = json.loads(message_data)
    else:
        raise ValueError('Data sector is missing in the Pub/Sub message.')

    text = validate_message(message, 'text')
    filename = validate_message(message, 'filename')
    target_lang = validate_message(message, 'lang')
    src_lang = validate_message(message, 'src_lang')

    print('Translating text into {}.'.format(target_lang))
    translated_text = translate_client.translate(text,
                                                 target_language=target_lang,
                                                 source_language=src_lang)
    topic_name = os.environ['RESULT_TOPIC']
    message = {
        'text': translated_text['translatedText'],
        'filename': filename,
        'lang': target_lang,
    }
    message_data = json.dumps(message).encode('utf-8')
    topic_path = publisher.topic_path(project_id, topic_name)
    future = publisher.publish(topic_path, data=message_data)
    future.result()

Go


package ocr

import (
	"context"
	"encoding/json"
	"fmt"
	"log"

	"cloud.google.com/go/pubsub"
	"cloud.google.com/go/translate"
)

// TranslateText is executed when a message is published to the Cloud Pub/Sub
// topic specified by the TRANSLATE_TOPIC environment variable, and translates
// the text using the Google Translate API.
func TranslateText(ctx context.Context, event PubSubMessage) error {
	if err := setup(ctx); err != nil {
		return fmt.Errorf("setup: %v", err)
	}
	if event.Data == nil {
		return fmt.Errorf("empty data")
	}
	var message ocrMessage
	if err := json.Unmarshal(event.Data, &message); err != nil {
		return fmt.Errorf("json.Unmarshal: %v", err)
	}

	log.Printf("Translating text into %s.", message.Lang.String())
	opts := translate.Options{
		Source: message.SrcLang,
	}
	translateResponse, err := translateClient.Translate(ctx, []string{message.Text}, message.Lang, &opts)
	if err != nil {
		return fmt.Errorf("Translate: %v", err)
	}
	if len(translateResponse) == 0 {
		return fmt.Errorf("Empty Translate response")
	}
	translatedText := translateResponse[0]

	messageData, err := json.Marshal(ocrMessage{
		Text:     translatedText.Text,
		FileName: message.FileName,
		Lang:     message.Lang,
		SrcLang:  message.SrcLang,
	})
	if err != nil {
		return fmt.Errorf("json.Marshal: %v", err)
	}

	topic := pubsubClient.Topic(resultTopic)
	ok, err := topic.Exists(ctx)
	if err != nil {
		return fmt.Errorf("Exists: %v", err)
	}
	if !ok {
		topic, err = pubsubClient.CreateTopic(ctx, resultTopic)
		if err != nil {
			return fmt.Errorf("CreateTopic: %v", err)
		}
	}
	msg := &pubsub.Message{
		Data: messageData,
	}
	if _, err = topic.Publish(ctx, msg).Get(ctx); err != nil {
		return fmt.Errorf("Get: %v", err)
	}
	log.Printf("Sent translation: %q", translatedText.Text)
	return nil
}

Java


import com.google.cloud.functions.BackgroundFunction;
import com.google.cloud.functions.Context;
import com.google.cloud.pubsub.v1.Publisher;
import com.google.cloud.translate.v3.LocationName;
import com.google.cloud.translate.v3.TranslateTextRequest;
import com.google.cloud.translate.v3.TranslateTextResponse;
import com.google.cloud.translate.v3.TranslationServiceClient;
import com.google.protobuf.ByteString;
import com.google.pubsub.v1.ProjectTopicName;
import com.google.pubsub.v1.PubsubMessage;
import functions.eventpojos.PubSubMessage;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.concurrent.ExecutionException;
import java.util.logging.Level;
import java.util.logging.Logger;

public class OcrTranslateText implements BackgroundFunction<PubSubMessage> {
  private static final Logger logger = Logger.getLogger(OcrTranslateText.class.getName());

  // TODO<developer> set these environment variables
  private static final String PROJECT_ID = getenv("GCP_PROJECT");
  private static final String RESULTS_TOPIC_NAME = getenv("RESULT_TOPIC");
  private static final String LOCATION_NAME = LocationName.of(PROJECT_ID, "global").toString();

  private Publisher publisher;

  public OcrTranslateText() throws IOException {
    publisher = Publisher.newBuilder(
        ProjectTopicName.of(PROJECT_ID, RESULTS_TOPIC_NAME)).build();
  }

  @Override
  public void accept(PubSubMessage pubSubMessage, Context context) {
    OcrTranslateApiMessage ocrMessage = OcrTranslateApiMessage.fromPubsubData(
        pubSubMessage.getData().getBytes(StandardCharsets.UTF_8));

    String targetLang = ocrMessage.getLang();
    logger.info("Translating text into " + targetLang);

    // Translate text to target language
    String text = ocrMessage.getText();
    TranslateTextRequest request =
        TranslateTextRequest.newBuilder()
            .setParent(LOCATION_NAME)
            .setMimeType("text/plain")
            .setTargetLanguageCode(targetLang)
            .addContents(text)
            .build();

    TranslateTextResponse response;
    try (TranslationServiceClient client = TranslationServiceClient.create()) {
      response = client.translateText(request);
    } catch (IOException e) {
      // Log error (since IOException cannot be thrown by a function)
      logger.log(Level.SEVERE, "Error translating text: " + e.getMessage(), e);
      return;
    }
    if (response.getTranslationsCount() == 0) {
      return;
    }

    String translatedText = response.getTranslations(0).getTranslatedText();
    logger.info("Translated text: " + translatedText);

    // Send translated text to (subsequent) Pub/Sub topic
    String filename = ocrMessage.getFilename();
    OcrTranslateApiMessage translateMessage = new OcrTranslateApiMessage(
        translatedText, filename, targetLang);
    try {
      ByteString byteStr = ByteString.copyFrom(translateMessage.toPubsubData());
      PubsubMessage pubsubApiMessage = PubsubMessage.newBuilder().setData(byteStr).build();

      publisher.publish(pubsubApiMessage).get();
      logger.info("Text translated to " + targetLang);
    } catch (InterruptedException | ExecutionException e) {
      // Log error (since these exception types cannot be thrown by a function)
      logger.log(Level.SEVERE, "Error publishing translation save request: " + e.getMessage(), e);
    }
  }

  // Avoid ungraceful deployment failures due to unset environment variables.
  // If you get this warning you should redeploy with the variable set.
  private static String getenv(String name) {
    String value = System.getenv(name);
    if (value == null) {
      logger.warning("Environment variable " + name + " was not set");
      value = "MISSING";
    }
    return value;
  }
}

Saving the translations

Finally, the following function receives the translated text and saves it back to Cloud Storage:

Node.js

/**
 * This function is exported by index.js, and is executed when
 * a message is published to the Cloud Pub/Sub topic specified
 * by the RESULT_TOPIC environment variable. The function saves
 * the data packet to a file in GCS.
 *
 * @param {object} event The Cloud Pub/Sub Message object.
 * @param {string} {messageObject}.data The "data" property of the Cloud Pub/Sub
 * Message. This property will be a base64-encoded string that you must decode.
 */
exports.saveResult = async (event) => {
  const pubsubData = event.data;
  const jsonStr = Buffer.from(pubsubData, 'base64').toString();
  const {text, filename, lang} = JSON.parse(jsonStr);

  if (!text) {
    throw new Error(
      'Text not provided. Make sure you have a "text" property in your request'
    );
  }
  if (!filename) {
    throw new Error(
      'Filename not provided. Make sure you have a "filename" property in your request'
    );
  }
  if (!lang) {
    throw new Error(
      'Language not provided. Make sure you have a "lang" property in your request'
    );
  }

  console.log(`Received request to save file ${filename}`);

  const bucketName = process.env.RESULT_BUCKET;
  const newFilename = renameImageForSave(filename, lang);
  const file = storage.bucket(bucketName).file(newFilename);

  console.log(`Saving result to ${newFilename} in bucket ${bucketName}`);

  await file.save(text);
  console.log(`File saved.`);
};

Python

def save_result(event, context):
    if event.get('data'):
        message_data = base64.b64decode(event['data']).decode('utf-8')
        message = json.loads(message_data)
    else:
        raise ValueError('Data sector is missing in the Pub/Sub message.')

    text = validate_message(message, 'text')
    filename = validate_message(message, 'filename')
    lang = validate_message(message, 'lang')

    print('Received request to save file {}.'.format(filename))

    bucket_name = os.environ['RESULT_BUCKET']
    result_filename = '{}_{}.txt'.format(filename, lang)
    bucket = storage_client.get_bucket(bucket_name)
    blob = bucket.blob(result_filename)

    print('Saving result to {} in bucket {}.'.format(result_filename,
                                                     bucket_name))

    blob.upload_from_string(text)

    print('File saved.')

Go


package ocr

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
)

// SaveResult is executed when a message is published to the Cloud Pub/Sub topic
// specified by the RESULT_TOPIC environment vairable, and saves the data packet
// to a file in GCS.
func SaveResult(ctx context.Context, event PubSubMessage) error {
	if err := setup(ctx); err != nil {
		return fmt.Errorf("ProcessImage: %v", err)
	}
	var message ocrMessage
	if event.Data == nil {
		return fmt.Errorf("Empty data")
	}
	if err := json.Unmarshal(event.Data, &message); err != nil {
		return fmt.Errorf("json.Unmarshal: %v", err)
	}
	log.Printf("Received request to save file %q.", message.FileName)

	resultFilename := fmt.Sprintf("%s_%s.txt", message.FileName, message.Lang)
	bucket := storageClient.Bucket(resultBucket)

	log.Printf("Saving result to %q in bucket %q.", resultFilename, resultBucket)

	w := bucket.Object(resultFilename).NewWriter(ctx)
	defer w.Close()
	fmt.Fprint(w, message.Text)

	log.Printf("File saved.")
	return nil
}

Java


import com.google.cloud.functions.BackgroundFunction;
import com.google.cloud.functions.Context;
import com.google.cloud.storage.BlobId;
import com.google.cloud.storage.BlobInfo;
import com.google.cloud.storage.Storage;
import com.google.cloud.storage.StorageOptions;
import functions.eventpojos.PubSubMessage;
import java.nio.charset.StandardCharsets;
import java.util.logging.Logger;

public class OcrSaveResult implements BackgroundFunction<PubSubMessage> {
  // TODO<developer> set this environment variable
  private static final String RESULT_BUCKET = System.getenv("RESULT_BUCKET");

  private static final Storage STORAGE = StorageOptions.getDefaultInstance().getService();
  private static final Logger logger = Logger.getLogger(OcrSaveResult.class.getName());

  @Override
  public void accept(PubSubMessage pubSubMessage, Context context) {
    OcrTranslateApiMessage ocrMessage = OcrTranslateApiMessage.fromPubsubData(
        pubSubMessage.getData().getBytes(StandardCharsets.UTF_8));

    logger.info("Received request to save file " +  ocrMessage.getFilename());

    String newFileName = String.format(
        "%s_to_%s.txt", ocrMessage.getFilename(), ocrMessage.getLang());

    // Save file to RESULT_BUCKET with name newFileNaem
    logger.info(String.format("Saving result to %s in bucket %s", newFileName, RESULT_BUCKET));
    BlobInfo blobInfo = BlobInfo.newBuilder(BlobId.of(RESULT_BUCKET, newFileName)).build();
    STORAGE.create(blobInfo, ocrMessage.getText().getBytes(StandardCharsets.UTF_8));
    logger.info("File saved");
  }
}

Deploying the functions

This section describes how to deploy your functions.

  1. To deploy the image processing function with a Cloud Storage trigger, run the following command in the directory that contains the sample code (or in the case of Java, the pom.xml file):

    Node.js

    gcloud functions deploy ocr-extract \
    --runtime nodejs10 \
    --trigger-bucket YOUR_IMAGE_BUCKET_NAME \
    --entry-point processImage \
    --set-env-vars "^:^GCP_PROJECT=YOUR_GCP_PROJECT_ID:TRANSLATE_TOPIC=YOUR_TRANSLATE_TOPIC_NAME:TO_LANG=es,en,fr,ja"
    You can use the following values for the --runtime flag to specify your preferred Node.js version:
    • nodejs10
    • nodejs12

    Python

    gcloud functions deploy ocr-extract \
    --runtime python37 \
    --trigger-bucket YOUR_IMAGE_BUCKET_NAME \
    --entry-point process_image \
    --set-env-vars "^:^GCP_PROJECT=YOUR_GCP_PROJECT_ID:TRANSLATE_TOPIC=YOUR_TRANSLATE_TOPIC_NAME:TO_LANG=es,en,fr,ja"
    You can use the following values for the --runtime flag to specify your preferred Python version:
    • python37
    • python38

    Go

    gcloud functions deploy ocr-extract \
    --runtime go111 \
    --trigger-bucket YOUR_IMAGE_BUCKET_NAME \
    --entry-point ProcessImage \
    --set-env-vars "^:^GCP_PROJECT=YOUR_GCP_PROJECT_ID:TRANSLATE_TOPIC=YOUR_TRANSLATE_TOPIC_NAME:TO_LANG=es,en,fr,ja"
    You can use the following values for the --runtime flag to specify your preferred Go version:
    • go111
    • go113

    Java

    gcloud functions deploy ocr-extract \
    --entry-point functions.OcrProcessImage \
    --runtime java11 \
    --memory 512MB \
    --trigger-bucket YOUR_IMAGE_BUCKET_NAME \
    --set-env-vars "^:^GCP_PROJECT=YOUR_GCP_PROJECT_ID:TRANSLATE_TOPIC=YOUR_TRANSLATE_TOPIC_NAME:TO_LANG=es,en,fr,ja"

    where YOUR_IMAGE_BUCKET_NAME is the name of your Cloud Storage bucket where you will be uploading images.

  2. To deploy the text translation function with a Cloud Pub/Sub trigger, run the following command in the directory that contains the sample code (or in the case of Java, the pom.xml file):

    Node.js

    gcloud functions deploy ocr-translate \
    --runtime nodejs10 \
    --trigger-topic YOUR_TRANSLATE_TOPIC_NAME \
    --entry-point translateText \
    --set-env-vars "GCP_PROJECT=YOUR_GCP_PROJECT_ID,RESULT_TOPIC=YOUR_RESULT_TOPIC_NAME"
    You can use the following values for the --runtime flag to specify your preferred Node.js version:
    • nodejs10
    • nodejs12

    Python

    gcloud functions deploy ocr-translate \
    --runtime python37 \
    --trigger-topic YOUR_TRANSLATE_TOPIC_NAME \
    --entry-point translate_text \
    --set-env-vars "GCP_PROJECT=YOUR_GCP_PROJECT_ID,RESULT_TOPIC=YOUR_RESULT_TOPIC_NAME"
    You can use the following values for the --runtime flag to specify your preferred Python version:
    • python37
    • python38

    Go

    gcloud functions deploy ocr-translate \
    --runtime go111 \
    --trigger-topic YOUR_TRANSLATE_TOPIC_NAME \
    --entry-point TranslateText \
    --set-env-vars "GCP_PROJECT=YOUR_GCP_PROJECT_ID,RESULT_TOPIC=YOUR_RESULT_TOPIC_NAME"
    You can use the following values for the --runtime flag to specify your preferred Go version:
    • go111
    • go113

    Java

    gcloud functions deploy ocr-translate \
    --entry-point functions.OcrTranslateText \
    --runtime java11 \
    --memory 512MB \
    --trigger-topic YOUR_TRANSLATE_TOPIC_NAME \
    --set-env-vars "GCP_PROJECT=YOUR_GCP_PROJECT_ID,RESULT_TOPIC=YOUR_RESULT_TOPIC_NAME"

  3. To deploy the function that saves results to Cloud Storage with a Cloud Pub/Sub trigger, run the following command in the directory that contains the sample code (or in the case of Java, the pom.xml file):

    Node.js

    gcloud functions deploy ocr-save \
    --runtime nodejs10 \
    --trigger-topic YOUR_RESULT_TOPIC_NAME \
    --entry-point saveResult \
    --set-env-vars "RESULT_BUCKET=YOUR_RESULT_BUCKET_NAME"
    You can use the following values for the --runtime flag to specify your preferred Node.js version:
    • nodejs10
    • nodejs12

    Python

    gcloud functions deploy ocr-save \
    --runtime python37 \
    --trigger-topic YOUR_RESULT_TOPIC_NAME \
    --entry-point save_result \
    --set-env-vars "RESULT_BUCKET=YOUR_RESULT_BUCKET_NAME"
    You can use the following values for the --runtime flag to specify your preferred Python version:
    • python37
    • python38

    Go

    gcloud functions deploy ocr-save \
    --runtime go111 \
    --trigger-topic YOUR_RESULT_TOPIC_NAME \
    --entry-point SaveResult \
    --set-env-vars "RESULT_BUCKET=YOUR_RESULT_BUCKET_NAME"
    You can use the following values for the --runtime flag to specify your preferred Go version:
    • go111
    • go113

    Java

    gcloud functions deploy ocr-save \
    --entry-point functions.OcrSaveResult \
    --runtime java11 \
    --memory 512MB \
    --trigger-topic YOUR_RESULT_TOPIC_NAME \
    --set-env-vars "RESULT_BUCKET=YOUR_RESULT_BUCKET_NAME"

Uploading an image

  1. Upload an image to your image Cloud Storage bucket:

    gsutil cp PATH_TO_IMAGE gs://YOUR_IMAGE_BUCKET_NAME
    

    where

    • PATH_TO_IMAGE is a path to an image file (that contains text) on your local system.
    • YOUR_IMAGE_BUCKET_NAME is the name of the bucket where you are uploading images.

    You can download one of the images from the sample project.

  2. Watch the logs to be sure the executions have completed:

    gcloud functions logs read --limit 100
    
  3. You can view the saved translations in the Cloud Storage bucket specified by the RESULT_BUCKET value in your configuration file.

Cleaning up

To avoid incurring charges to your Google Cloud Platform account for the resources used in this tutorial:

Deleting the project

The easiest way to eliminate billing is to delete the project that you created for the tutorial.

To delete the project:

  1. In the Cloud Console, go to the Manage resources page.

    Go to the Manage resources page

  2. In the project list, select the project that you want to delete and then click Delete .
  3. In the dialog, type the project ID and then click Shut down to delete the project.

Deleting the Cloud Functions

Deleting Cloud Functions does not remove any resources stored in Cloud Storage.

To delete the Cloud Functions you created in this tutorial, run the following commands:

gcloud functions delete ocr-extract
gcloud functions delete ocr-translate
gcloud functions delete ocr-save

You can also delete Cloud Functions from the Google Cloud Console.