What is the difference between bitonal, grayscale, and color scanning and when should you use each?

When you digitize records, one of the first decisions is the capture mode, or how much tonal information the scanner records for each pixel. The three common choices are bitonal, grayscale, and color. Each balances image quality against file size and processing effort differently, so the right answer depends on what the document actually contains and how the digital copy will be used.

The three modes

• Bitonal (black-and-white): Each pixel is recorded as either pure black or pure white, with no shades in between. Files are small and text is crisp, but any subtle tonal detail (faint pencil, shading, photographs) is lost.
• Grayscale: Each pixel captures a range of gray tones from black to white. This preserves shading, faded text, and the appearance of pencil or carbon copies, at the cost of larger files than bitonal.
• Color: Each pixel records the full range of hues. Color is essential when the colors themselves carry meaning, but it produces the largest files.

When to use each

• Use bitonal for clean, high-contrast textual documents: printed forms, typed correspondence, and faxes where only the legibility of the text matters. It is efficient for high-volume scanning and works well with OCR and text search.
• Use grayscale when documents contain handwriting, pencil notes, halftone images, faded or low-contrast text, or signatures whose tonal subtlety matters. Grayscale is often a safe middle ground when bitonal loses too much detail but color adds no real value.
• Use color when color conveys information or evidentiary value: maps, charts, photographs, color-coded forms, stamps, seals, or originals where authenticity and visual fidelity matter. Color is also appropriate for permanent or archival records where you want to capture the document as completely as possible.

A guiding principle

Match the capture mode to the informational value and intended use of the record, not to the lowest file size. Under-capturing (for example, scanning a faded or color-coded original in bitonal) can permanently lose information, since rescanning may not be possible once originals are dispositioned. Established imaging guidelines recommend selecting resolution and color depth based on document characteristics and preservation goals.

For broader context on capture standards, resolution, and quality control, see the digitization and imaging hub.