OCR a scanned PDF

The shortest useful pipeline, and the right starting point for a scan with no text layer.

import { Pipeline, ImageDrawBoxes, configure } from '@stabrise/scaledp'
import { PdfToImage } from '@stabrise/scaledp/pdf'
import { PaddleTextRecognizer } from '@stabrise/scaledp/ocr'

configure({
    cache: 'indexeddb',
    pdf: {
        workerSrc: '/pdf.worker.min.mjs',
        cMapUrl: '/cmaps/',
        standardFontDataUrl: '/standard_fonts/',
    },
})

const pipeline = new Pipeline([
    new PdfToImage({ resolution: 300 }),
    new PaddleTextRecognizer({ preset: 'v6-small', keepFormatting: true }),
    new ImageDrawBoxes({
        inputCols: ['image', 'text'],
        outputCol: 'annotated',
        color: '#3fc9f5',
        lineWidth: 2,
    }),
])

const rows = await pipeline.transform(file)

Open in builder

One row per page:

import { renderInto, showImage, showText } from '@stabrise/scaledp/display'

for (const row of rows) {
    if (row.text.exception) {
        console.warn(`page ${row.page}:`, row.text.exception)
        continue
    }
    renderInto('#page', showImage(row.annotated))
    renderInto('#text', showText(row.text))
}

Turning the dials

Too slow. Drop resolution to 150 — it quarters the pixel count. Try preset: 'v6-tiny'. Prefer WebGPU:

import { isWebGpuAvailable } from '@stabrise/scaledp/ocr'
configure({ executionProviders: (await isWebGpuAvailable()) ? ['webgpu', 'wasm'] : ['wasm'] })

Wrong script. v6-small covers Latin and CJK. For anything else, pick a v5 preset — or let the page choose:

import { detectScript, presetsForScript } from '@stabrise/scaledp/ocr'

const detected = await detectScript(canvas)
const options = detected ? await presetsForScript(detected.script) : []

Skewed or rotated text. PaddleOCR detects internally and does not handle rotation especially well. Use a real detector and a separate recognizer.

Only some pages need this. If the PDF is a mix, check the text layer first — see Skip OCR when there is a text layer.

The tab freezes. Move it off the main thread: Run off the main thread.

Turning the dials

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