ocr-parser
This library provides a simple interface to parse OCR data from a stream, buffer or string. It does not rely on any DOM APIs and can therefore be used in contexts where there is no built-in support for XML parsing, most notabily in Web Workers and Service Workers.
Currently the library supports hOCR and ALTO OCR markup.
Usage
Before OCR markup can be parsed, the XML parser has to be initialized. The
library uses sax-wasm under the hood,
which needs to be initialized with its WASM code before it can be used. By
default, the WASM will be loaded from unpkg.com
, but you can also provide a
custom callback to the initialize
function to load the WASM from a different
source. Make sure that the WASM matches the versio of sax-wasm
used by this
library (currently 2.2.4
).
import { initialize as initializeXmlParser } from 'ocr-parser';
// Load from unpkg.com
await initializeXmlParser();
// Load from custom source (e.g. from base64-encoded constant)
await initializeXmlParser(() => Promise.resolve(WASM_BLOB));
Once the parser has been initialized, call parseOcrPages
or any of
the format-specific functons (parseAltoPages
, parseHocrPages
) with
your markup to retrieve an asynchronous generator over all the pages
in the markup.
import { parseOcrPages } from 'ocr-parser';
for await (const page of parseOcrPages(markup, 'hocr')) {
// Do something with the page
console.log(page);
}
Data Structures
The markup is parsed into a simple hierarchical data structure:
OcrPage
└── OcrBlock
└── OcrParagraph
└── OcrLine
├── OcrWord
└── string
The OcrBlock
and OcrParagraph
levels are only present if they are encoded in
the markup. Every element has getters for any of the lower levels, so yo can
simply access OcrPage#words
to get a flat list of all words on the page.
string
children of OcrLine
elements are 'stray' text nodes (including whitespace) that are not explicitely encoded as words (and thus have no associated bounding box).