Make a scanned PDF black & white — 3–5× smaller
A phone scan of a one-page certificate is mostly paper, yet a colour JPEG spends bytes describing the exact shade of grey-yellow that paper is. Black & white throws that away: KBcut evens out shadows, pushes the paper to pure white and the ink to pure black, then stores each page as a real 1-bit image. Text documents typically come out three to five times smaller than the colour version at the same sharpness.
Made for
- Marksheets, degree and caste certificates that are printed black on white
- Rent agreements, electricity bills and NOCs for address proof
- Typed notices, affidavits and letters you signed and scanned
- Multi-page photocopies that a portal wants under 100 or 200 KB
How the options work
- Black & white (1-bit) — each pixel is black or white, compressed losslessly. Smallest and sharpest for text, signatures and stamps.
- Greyscale — keeps shades, drops colour. Use it when there is a photo on the page (ID cards, admit cards) or a faint pencil entry.
- Colour — only when the reviewer must see a coloured seal, a hologram or a highlighted entry.
- The target KB still applies: if 1-bit at high resolution is already under the cap you get the sharpest version; if not, resolution steps down until it fits.
- Pages are rebuilt as images, so text is no longer selectable. Portals do not care; do not use it on a PDF you still need to edit.
Why a generic compressor gets this wrong
The reason this works so well is how the two formats spend bytes. JPEG was designed for photographs: smooth gradients compress well, sharp black-on-white edges do not, and every edge sprouts faint "ringing" that costs data. A 1-bit image stored with lossless compression is the opposite — long runs of white paper collapse to almost nothing and letter edges stay razor sharp. That is why a 900 KB colour scan of a two-page certificate can land near 150 KB in black & white with no visible loss of legibility, while squeezing the same scan to 150 KB as colour JPEG turns the text to mush.
How to do it
- Select the PDF, or photos of the pages (they become one PDF in the order you pick them).
- Leave Colour on Black & white, or choose Greyscale if the page has a photograph.
- Type the portal cap in KB — or tap a quick size — and press Cut to size. The preview shows page one exactly as the portal will see it.
Questions
My stamp or signature disappeared.
Very light blue ink can fall on the paper side of the threshold. Switch to Greyscale, which keeps faint strokes, or rescan with darker ink in daylight.
Is 1-bit accepted by government portals?
Yes. Portals check the file type (PDF) and size, not the colour depth. Black & white is how office scanners have sent documents for decades.
Why is the black & white file bigger than my colour one?
Only when the page is mostly photograph — halftone dots are expensive in 1-bit. Use Greyscale for those pages.
Does my document leave the phone?
No. Rendering, cleaning and compression all run in this browser tab. You can turn on flight mode after the page loads.
Can I get black & white JPEGs instead of a PDF?
Yes — set Output to JPEG. Each page becomes a black & white JPEG under the cap. JPEG cannot store true 1-bit pixels, so the files are a little larger than the PDF version.