OCR without temporary input files¶

StreamingTesseractEngine is an explicit adapter for a locally installed Tesseract executable and language data. It encodes one image in memory and uses Tesseract's documented stdin/stdout interface with TSV output. It does not download models, change the default OCR engine, or create temporary image/text files. Tesseract command-line reference

from openmed.multimodal.ocr import ocr
from openmed.multimodal.ocr_tesseract_stream import StreamingTesseractEngine

engine = StreamingTesseractEngine(
    timeout_seconds=30,
    max_pixels=16_000_000,
    max_words=25_000,
    max_text_chars=100_000,
)
result = ocr("local-synthetic-scan.png", engine=engine, languages=["de", "en"])
document = result.to_document(preserve_lines=True)

Pillow and the native Tesseract binary/language files are required. The adapter accepts a Pillow image, encoded image bytes, a path or a binary image stream. Input must contain one frame. The pixel budget is checked before conversion; transparent pixels are composited on white without changing source dimensions. Coordinates refer to decoded pixels; EXIF orientation is not applied. The native deadline applies to Tesseract execution, not image decoding. A hosting service must separately bound its entire ingestion request and isolate native image/PDF parsing.

Native output is read while input is written, preventing pipe deadlocks. A deadline or optional thread-safe cancel_check stops and reaps the owned OCR process. TSV output is bounded before accumulating it, and word/text limits are checked during parsing. Native stderr and exception details are excluded from errors. The process receives a restricted environment and one OpenMP thread. An explicit executable or tessdata_dir is trusted host configuration; neither should be supplied by untrusted document content or request arguments.

Returned words retain zero-based page indexes, pixel rectangles, normalized confidence and numeric block/paragraph/line identifiers. Invalid UTF-8, malformed records, duplicate word IDs, unsupported languages and invalid/out-of-image geometry fail explicitly. Confidence is an OCR score, not a calibrated estimate of clinical correctness. Empty OCR output may represent either a blank image or missed content; it is not a completeness guarantee.

result.text keeps the common space-joined OCR contract. For clinical headings, use result.to_document(preserve_lines=True) to retain the native engine's line boundaries and word order. This conversion requires valid, contiguous native line IDs and preserves each word's page, confidence and rectangle. With the default single-space separator, word offsets also remain unchanged. Review reading order separately, especially for columns or tables; this conversion does not reconstruct layout or establish content completeness. OCR outputs remain preview; no clinical language or privacy capability is qualified by this adapter. It performs OCR only, without redacting pixels, sanitizing a PDF, or verifying that all identifiers were found.