TabBench

How to compress an image or signature to 20KB

Updated

A 20KB limit almost always means a signature field rather than a photograph. Exam and banking portals typically ask for a signature between 10KB and 20KB, often at around 140×60 pixels, and they reject anything larger without explanation.

Signatures compress very differently from photographs. A signature is dark strokes on white — mostly flat area with sharp edges — which is the worst case for JPEG and the best case for aggressive resizing. Handling it like a photograph is why people end up with a grey, smudged scrawl.

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Step by step

  1. Crop tight to the signature itself

    Remove all the surrounding paper. A signature occupying 90% of the frame at 140×60 is far clearer than one floating in a scan of a whole sheet, and dramatically smaller.

  2. Increase contrast before compressing if the scan is grey

    A phone photo of a signature often has a grey cast. Pushing it toward true black on true white both improves legibility and compresses better, because flat white areas cost almost nothing to store.

  3. Resize to the portal's stated dimensions

    Commonly 140×60. At that size, hitting 20KB requires almost no quality compression at all — the resize does essentially all the work.

  4. Target 20KB and check the strokes

    Look for broken or faded strokes at 100%. If they appear, the dimensions are fine but the quality floor is too low — usually a sign the image is still larger than it needs to be.

Things worth knowing

  • Sign on plain white unlined paper in black or dark blue ink. Lined paper adds detail that wastes your byte budget and confuses reviewers.
  • Scan or photograph straight on. A skewed signature often fails automated checks even when it is under the size limit.
  • If the portal offers a 10KB limit, the same approach works — go to 120×50 rather than compressing harder.

Frequently Asked Questions

Why does my signature look faded after compressing?

JPEG smooths sharp edges, and a signature is nothing but sharp edges. Fix it by resizing rather than compressing harder, and by increasing contrast first so the strokes are genuinely black rather than dark grey.

What dimensions should a signature be?

Check your portal, but 140×60 pixels is the most common requirement on Indian exam and banking forms. Some accept up to 300×80. The stated dimensions almost always matter as much as the file size.

Can I use PNG for a signature?

If the portal accepts it, yes — PNG handles sharp black-on-white strokes better than JPEG and can be very small for this kind of image. Many portals only accept JPEG, so check first.