Bitonal Imaging
Bitonal imaging is a digitization method that captures each pixel of a document as one of only two values—pure black or pure white—producing a high-contrast, low-storage image well suited to clean text and line documents.
Bitonal imaging (also called 1-bit or black-and-white scanning) records every pixel as a single binary value, so the resulting image contains no grayscale or color information. Because each pixel needs only one bit, bitonal files are dramatically smaller than grayscale or color captures and compress efficiently, which is why high-volume scanning of typewritten correspondence, forms, and printed text historically relied on it. In recordkeeping, the trade-off matters: bitonal capture preserves crisp legibility and supports fast optical character recognition for clean originals, but it discards subtle tonal detail and can lose faint pencil notes, stamps, signatures, watermarks, photographs, or aged paper gradations. For that reason, preservation and archival reformatting programs generally specify grayscale or color capture for materials where tone carries evidential or informational value, reserving bitonal for documents that are genuinely two-tone. Choosing an appropriate capture mode is part of demonstrating that a digital surrogate is a faithful, trustworthy reproduction—an authenticity concern that runs through digitization appraisal, transfer planning, and the metadata that documents how each file was created.