Resize a signature to 10KB

Ten kilobytes sounds impossible until you realise what a signature actually is: a few thin dark lines on a large field of white. That is the cheapest thing an image encoder will ever be asked to store, and the limit is comfortable once the picture contains nothing but the signature itself.

How should the settings be chosen?

    Almost all of the weight is background

    A signature photographed on a desk carries the desk, the edge of the notebook, a shadow falling across one corner and whatever else was in shot. Every one of those is texture, and texture is what costs bytes. The ink itself is almost free.

    Crop hard, until the frame holds the signature and a thin margin and nothing else. Most people find the file drops below the limit at this point alone, before any quality setting has been touched.

    What actually breaks at ten kilobytes

    Strokes going grey and patchy is the failure to watch for. It happens when the paper was photographed unevenly, so the white is not really white — it is a hundred slightly different greys, and the encoder spends its budget describing them instead of the ink.

    Even lighting fixes this far better than any setting. Photograph near a window with the light coming from the side rather than over your shoulder, so no shadow of your hand or phone falls across the paper.

    Width matters more than quality here

    A signature does not need many pixels. Four hundred across is generous for something that will be printed at a couple of centimetres, and halving the width removes three quarters of the pixels. Reach for the width before you reach for the quality slider, because width costs you nothing you can see and quality eventually does.

    Questions

    My signature looks faded after compressing. What went wrong?
    The original was probably grey rather than black to begin with. A pencil signature, a drying ballpoint, or a photograph taken in dim light all produce strokes that are already mid-grey, and compression pushes them further toward the background. Sign again with a fresh black or dark blue pen, photograph it in daylight, and it will survive far better.
    Should I scan or photograph the signature?
    A scan is easier to get right because the lighting is controlled and the paper stays flat, but a phone photograph is perfectly acceptable if you shoot in even daylight from directly above. What matters is that the paper is evenly lit and square to the camera, not which device produced the image.
    The form rejects my file even though it is under 10KB.
    File size is usually only one of several conditions. Check the accepted format, the pixel dimensions and the aspect ratio on the instruction page for your form. Many portals also reject images that are too small in pixels even when the file size is comfortable, because the printed result would be illegible.

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