Tesseract OCR Service

An AWS Lambda function that performs OCR on an image hosted at a specified URL

This project was made to experiment with self-hosting Tesseract.js to perform OCR on a serverless platform like AWS Lambda. It turned out to be a great way to learn about AWS Lambda & the Serverless Framework, so here's my code, have at it.

Getting Started

Install required dependencies

npm install

Spin up the server

A menu of options is provided with

npm run start

Spin up a Serverless instance on your localhost (port 3000 by default) with the command

npm run start-offline

API

GET /ocr

Param: image_url

Performs OCR of the image hosted at image_url and returns all of the textual information Tesseract can find.

Example GET request

http://localhost:3000/ocr?image_url=https://zdnet3.cbsistatic.com/hub/i/r/2017/12/12/67b1a674-c8a8-415a-b57b-7e5961fee2cc/resize/770xauto/c6c18e77cbc0b9f74d4ed1dd6c7d4cb4/screen-shot-2017-12-11-at-11-13-50-pm.png

Returns

{
    statusCode: 200,
    body: {
        result: "' Netflix us 0 v\\n©netih><\\nTo the 53 people who've watched A\\nChristmas Prince every day for the past 18\\ndays: Who hurt you?\\n9:52 PM 710 Dec 2017\\n102,579 Retweets 403,055 kaes ‘qujflg Q6; %\\nO 7.2K U, 103K (7 403K 8\\n\\n\"
    }
}

Unit Tests

There aren't any tests right now, but I made a template for your convenience at ./src/test/ocr.test.js.

Run tests with

npm run test

Setting up your AWS Lambda Service

I assume you have already created an AWS Lambda Service and configured your local desktop environment (e.g. AWS credentials, CLI) to be able to deploy AWS services. If not, you can check out their official guide here.

Then, check out Serverless Framework here. It helps you to automate the deployment of your AWS infrastructure resources & lambda functions, using the serverless.yml template.

Deploying

Deploy the service to AWS Lambda with the help of Serverless

npm run deploy-prd

Or just deploy a lambda function without having to re-deploy the entire service

npm run deploy-func-serve-prd

---

Billing / Performance Estimation on AWS Lambda

FREE

No. of free tier seconds / month             = 266,667
Duration of a single OCR function invocation = 6.0s (estimated)
No. of free function invocations / month     = 40,000 - 45,000

PRICE THEREAFTER

Price per 0.1 seconds                = $0.000002501
Price per 1 second                   = $0.00002501
Price per function invocation        = $0.00002501 * 6.0s = $0.00015006
Price per 1000  function invocations = $0.15
Price per 10000 function invocations = $1.50

MEMORY USAGE

Ranged from 50MB (images with small resolution) to 700MB (images with large resolution). I had to provision my lambda service on AWS a pretty large memory capacity (like maybe ~1.5GB) to be able to cope with a wide range of image resolutions.