Spring Boot Tesseract OCR in Kotlin with multi-stage Docker

Create a Dockerfile and paste the following two code blocks in the same Dockerfile.

FROM amazoncorretto:11 as build
RUN yum update -y &&
    yum -y -q install wget &&
    yum install -y gcc gcc-c++ autoconfig automake make pkgconfig libtool gzip tar&&
    yum install -y zlib-devel libtiff-devel libwebp-devel libpng-devel  openjpeg2-devel lib-jpeg-turbo-devel giflib-devel &&
    yum clean all &&
    rm -rf /var/cache/yum

RUN wget -q https://github.com/DanBloomberg/leptonica/archive/refs/tags/1.82.0.tar.gz 
    && tar -zxvf 1.82.0.tar.gz -C /opt 
    && rm -f 1.82.0.tar.gz

WORKDIR /opt/leptonica-1.82.0
RUN ./autogen.sh
RUN ./configure
RUN make && make install

RUN wget -q https://github.com/tesseract-ocr/tesseract/archive/5.2.0.tar.gz 
    && tar -zxvf 5.2.0.tar.gz -C /opt 
    && rm -f 5.2.0.tar.gz

WORKDIR /opt/tesseract-5.2.0
RUN ./autogen.sh
RUN ./configure
RUN make && make install

RUN wget https://github.com/tesseract-ocr/tessdata/raw/main/eng.traineddata -P /opt/
RUN wget https://github.com/tesseract-ocr/tessdata/raw/main/osd.traineddata -P /opt/

b. Docker final stage

Extract only the required libraries to the final stage of the Dockerfile.

FROM amazoncorretto:11

WORKDIR /opt

ARG LD_LIBRARY_PATH=/usr/local/lib
ENV LD_LIBRARY_PATH ${LD_LIBRARY_PATH}
ENV PKG_CONFIG_PATH ${LIBRARY_PATH}/pkgconfig
ARG TESSDATA_PREFIX=/usr/local/share/tessdata
ENV TESSDATA_PREFIX ${TESSDATA_PREFIX}

COPY --from=build /usr/local/lib/libtesseract.so.5.0.2 ${LD_LIBRARY_PATH}/
COPY --from=build /usr/local/lib/liblept.so.5.0.4 ${LD_LIBRARY_PATH}/
COPY --from=build /lib64/libjpeg.so.62.3.0 ${LD_LIBRARY_PATH}/
COPY --from=build /lib64/libtiff.so.5.2.0 ${LD_LIBRARY_PATH}/
COPY --from=build /lib64/libwebp.so.4.0.2 ${LD_LIBRARY_PATH}/
COPY --from=build /lib64/libopenjp2.so.2.4.0 ${LD_LIBRARY_PATH}/
COPY --from=build /lib64/libgomp.so.1.0.0 ${LD_LIBRARY_PATH}/
COPY --from=build /lib64/libjbig.so.2.0 ${LD_LIBRARY_PATH}/

COPY --from=build /opt/*.traineddata ${TESSDATA_PREFIX}/

RUN echo ${LD_LIBRARY_PATH} >> /etc/ld.so.conf
RUN ldconfig

WORKDIR /app
COPY ./src/main/resources/static/tesseract.png tesseract.png
COPY ./src/main/resources/static/tesseract.pdf tesseract.pdf

COPY ./build/libs/tesseract-ocr-0.0.1.jar tesseract-ocr.jar

EXPOSE 8080
CMD ["java", "-jar", "tesseract-ocr.jar"]

Now we have optimised the size (Space complixity) of the Docker image.
But the build time (Time complexity) is increased to extract the binary of Tesseract and Leptonica.

Note: To optimise the time complexity, you can use any artifactory repository (ex. JFrog artifactory) and create a separate pipeline to push the binary of Tesseract, Leptonica, the Trained Data Set, and its dependency libraries as a one-time task. Later, you can download those binaries and data sets into your Docker image. It will reduce Docker build time.

IV. OCR operation

Add the Tesseract library to the build.gradle.kts file’s dependencies.

import org.jetbrains.kotlin.gradle.tasks.KotlinCompile

plugins {
 id("org.springframework.boot") version "2.7.12"
 id("io.spring.dependency-management") version "1.0.15.RELEASE"
 kotlin("jvm") version "1.6.21"
 kotlin("plugin.spring") version "1.6.21"
}

group = "com.example"
version = "0.0.1"
java.sourceCompatibility = JavaVersion.VERSION_11

repositories {
 mavenCentral()
}

dependencies {
 implementation("org.springframework.boot:spring-boot-starter-web")
 implementation("com.fasterxml.jackson.module:jackson-module-kotlin")
 implementation("org.jetbrains.kotlin:kotlin-reflect")
 testImplementation("org.springframework.boot:spring-boot-starter-test")
 implementation("net.sourceforge.tess4j:tess4j:5.4.0")
}

tasks.withType<KotlinCompile> {
 kotlinOptions {
  jvmTarget = "11"
 }
}

Create document type enums.

package com.example.ocr.pdf.enum

enum class DocumentType {
    PDF,PNG
}

In the following code, we are performing OCR operations for both PDF and images.
Text extraction is one of the use cases for the Tesseract library.

package com.example.ocr.pdf

import com.example.ocr.pdf.enum.DocumentType
import net.sourceforge.tess4j.Tesseract
import net.sourceforge.tess4j.TesseractException
import org.springframework.stereotype.Service
import java.io.File

@Service
class OCRService {

    fun getContent(documentType: DocumentType): String {
        val tesseract = Tesseract()

        try {
            val filePath = getFilePath(documentType)
            val image = File(filePath)

            tesseract.setDatapath(System.getenv(TESSDATA_PREFIX))
            tesseract.setLanguage("eng")
            tesseract.setVariable("tessedit_create_horc", "1")
            tesseract.setPageSegMode(1)
            tesseract.setOcrEngineMode(1)

            println("Document type ===> ${documentType.name}")
            return tesseract.doOCR(image)
        } catch (e: TesseractException) {
            throw Exception(e)
        }
    }

    fun getFilePath(documentType: DocumentType): String {
        return when (documentType) {
            DocumentType.PDF -> PDF_FILE
            DocumentType.PNG -> PNG_FILE
        }
    }

    companion object {
        const val TESSDATA_PREFIX = "TESSDATA_PREFIX"

        const val PDF_FILE = "tesseract.pdf"
        const val PNG_FILE = "tesseract.png"
    }
}

V. Github source code

https://github.com/thepurushoths/tesseract-ocr

If there are any other optimized approaches, then let me know in the comments. I will learn with you.

Thanks!