Compress a PNG to 100KB

PNG is lossless, which means there is no quality setting to lower — the format is obliged to reproduce every pixel exactly. That changes the whole approach: with a PNG you are choosing between fewer pixels and a different format, and pretending otherwise leads people to fiddle with a slider that does nothing.

How should the settings be chosen?

    Why the quality slider is disabled here

    Lossless means the decoded result is identical to the input, so there is nothing to trade away. A quality control would be a lie, and target size mode cannot work either, since the encoder has no dial to search over. DropKB disables both rather than letting you move a control that changes nothing.

    What does change a PNG size is the pixel count and the number of distinct colours. Both are real levers, and both are honest ones.

    What PNG is genuinely good at

    Large areas of a single colour, sharp edges and transparency. A screenshot, a logo, a chart or a diagram in PNG is often smaller than the same image as a JPG, and dramatically cleaner, because the format is built for exactly that content and never blurs an edge.

    For those images, resizing to the width you actually display is usually all that is needed to reach a hundred kilobytes.

    When to stop using PNG

    For a photograph, PNG is the wrong choice and no amount of resizing fixes that — it must store every subtle variation in every pixel, and a photograph is nothing but subtle variation. Convert to WebP or JPEG and the same picture reaches a hundred kilobytes at dimensions many times larger. Keep PNG only if you need transparency.

    Questions

    Why can I not set a target size for a PNG?
    Because target size mode works by searching for a quality level, and a lossless format has none. Every PNG encoding of a given image at given dimensions produces essentially the same size. To make a PNG smaller you reduce its dimensions, reduce its colour count, or change format.
    Will converting my PNG to WebP keep the transparency?
    Yes. WebP supports an alpha channel, so transparent areas survive the conversion and the file is usually much smaller than the PNG. JPEG does not support transparency — transparent pixels are filled with white, which DropKB does deliberately so a logo does not arrive on a black rectangle.
    My screenshot is a huge PNG. What should I do?
    Resize it to the width it will actually be viewed at, and keep it as PNG. Screenshots are mostly flat colour and sharp text, which PNG encodes efficiently and losslessly. Converting a text screenshot to JPEG makes the text blurry while frequently producing a larger file.
    Why is my PNG bigger than the JPG version of the same picture?
    Because lossless storage of a photograph is genuinely expensive. Every grain of sensor noise and every subtle shift in a sky must be recorded exactly rather than approximated, and photographs are made almost entirely of such variation. The lossy formats look identical to your eye because they discard precisely the variation your eye does not register.

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