Grayscale Compress for Black-and-White Scans

Grayscale Compress for Black-and-White Scans

Office scanners often save a black letter on white paper as a colour JPEG. The chroma channels are noise. FlashKit Tools’ PDF compressor has an optional grayscale tick that averages each pixel before JPEG so those channels stop costing bytes. It is not a 1-bit fax encoder and it will not touch JBIG2/CCITT pages.

Pair it with a kilobyte cap in compress to 200 KB or a labelled DPI in 150 / 200 DPI.

Tick grayscale for mono scans

Colour IDs stay in colour. Black-on-white letters usually shrink more than another quality click.

Open PDF Compressor

When the tick helps

  • A phone photo of a printed form, mostly white, black Times text, maybe a blue stamp.
  • A duplex office scan exported as colour JPEG inside a PDF (including inside a Form XObject).
  • Target Size 200 KB or 500 KB on those pages, after 150 DPI still overshoots.

When it hurts: a passport photo, a highlighted contract, a colour chart. The UI says “visual grayscale (RGB encoding for PDF compatibility)” so you are not surprised that the PDF ColorSpace is still DeviceRGB.

Step-by-step

  1. Drop the unlocked PDF. Encrypted files fail with an error.
  2. Tick Grayscale. In Target Size, pick 200 KB or 500 KB. In Quality mode, 150 DPI is a sensible scan start.
  3. Compress. Confirm the grayscale note and that text is still black, not brown mush.
  4. If the file is still over a portal cap, split annexes with Split PDF rather than stacking 50 DPI on grayscale.

Need a single gray JPEG of page 3 for a form that wants an image? PDF to JPG renders that page; the compressor does not export JPEGs.

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