The ladder
Open a PNG and the Quality tab shows the ladder: the same picture, with your background and your edge settings, written at quality 95, 90, 86, 80, 70 and 60. Every rung is a real file at full size, so its byte count is the size you would save. Beside each one is the share of the PNG it takes, a measured similarity figure, and a 96-pixel crop of the same spot at 1:1.
Press “Use this” on a rung and it becomes the recipe, on the undo stack like any other change. Move anything else — the matte, the size, the edge repair — and the ladder writes itself again for the new recipe.
What it will not tell you
- That a JPG is lossless. No quality setting makes it so; 1.000 similarity would mean identical pixels and a JPEG never quite gets there.
- That the marked rung is right for you. “Smallest that still looks right” is the lowest rung measuring at least 0.97, a threshold chosen by hand. It is labelled a judgement on the page.
- That compression always wins. If every rung is larger than the PNG, the verdict above Save says so and hands the PNG back.
Questions about compressing
- How much smaller will the JPG be?
- It depends entirely on the picture, which is why the page does not guess. It writes the file at six qualities — 95, 90, 86, 80, 70 and 60 — and prints each one's size and its share of the PNG. A photograph often drops to a tenth; a flat logo can come out larger than the PNG at every setting.
- What does the similarity number mean?
- It is SSIM on brightness, measured between the exact pixels handed to the encoder and the JPG decoded back: 1.000 is identical, and the figure falls as the encoder rounds more away. It is a measurement of this file, not a promise about how it looks to you, so each rung also shows a 1:1 crop.
- Which rung should I pick?
- The page marks the lowest rung that still measures 0.97 or more as “smallest that still looks right”. That threshold is a judgement chosen by hand, and it is labelled as one. Look at the crops: if text or fine lines matter, go one rung higher.
- Can I compress to 1 MB or another exact size?
- Yes, under Quality choose “Fit under a size”, or use the KB page, which searches for the highest quality under a ceiling with real encodes. The ladder is for choosing by eye; the size search is for meeting a limit.
- Is the picture uploaded to compress it?
- No. All six encodes happen in this tab, in a background worker where the browser has one. The ladder is six files written in memory and thrown away unless you pick one and save it.
Next steps
- PNG to JPG in KBWhen there is a hard limit to meet rather than a choice to make.
- PNG to JPG resizeFewer pixels is the biggest saving there is.
- When to keep the PNGThe pictures no quality setting will help.
