Grayscale uses many gray tones
A grayscale page can represent dark gray, medium gray, light gray and many intermediate levels between black and white.
That tonal range helps retain detail in photographs, shaded charts, scanned signatures and anti-aliased text edges.
Pure black and white uses only two pixel values
Pure B&W is a threshold operation. Each rendered pixel is measured for brightness and then assigned either black or white.
There are no intermediate gray tones, so the result looks more like a high-contrast photocopy than a grayscale photograph.
The threshold controls what becomes black
In 1into1 Pure B&W mode, pixels darker than the selected threshold become black and lighter pixels become white. The control ranges from 50 to 200 and defaults to 135.
Lower values make fewer pixels black and can thin text. Higher values darken more of the page, which can help faint scans but may also swallow light details.
Choose based on the source document
Use Smooth Grayscale when photographs, soft shading or tonal differences matter. Use Pure B&W when you want high-contrast text-and-line output and can accept loss of gray detail.
Preview page 1 and inspect the final file because no single threshold is ideal for every scanner, background tone or document type.
Both modes create an image-based PDF
The current 1into1 workflow renders the source pages and rebuilds the output using JPEG-backed page images in both modes.
The distinction is therefore about the pixel transform: grayscale keeps intermediate gray values, while Pure B&W reduces those rendered pixels to black or white.
Official sources reviewed
- Adobe Acrobat — How to make a PDF black and whiteExplains the difference between grayscale tonal depth and two-tone black-and-white output.
- Smallpdf — Print PDFs in black and whiteProvides a recent practical explanation of grayscale versus pure black-and-white output.