Resize PNG

Resizing runs through the browser's own image scaler with smoothing set to its highest quality setting, which is a genuinely good filter for photographs and for downscaling in general. Hard-edged UI graphics are the harder case: any resampler has to invent intermediate pixels, so a 100px icon taken to 73px will soften slightly no matter which tool does it. Scale by whole-number factors where you can — 512 to 256 to 128 stays crisp in a way 512 to 300 does not — and prefer generating each size from the largest original rather than from an already-resized copy.

Because PNG has nothing for it to control. It is a lossless format, and the browser canvas encoder ignores the quality parameter completely when the output type is PNG — a tool that shows you a PNG quality slider is showing you a control that does nothing. The only lever on a PNG's file size is how many pixels it contains, which is exactly what this tool changes. To make a PNG smaller without changing its dimensions, use PNG Compressor, which reduces the colour palette instead.

Not really, and no tool can. Upscaling has no extra detail to draw on, so it fills the new pixels by interpolating between the ones you already have — the result is a larger image with the same amount of real information, which reads as soft. It works acceptably for flat graphics and logos with few colours, and poorly for screenshots of text or for photographs. If a bigger version exists anywhere, start from that instead.

Auto-Crop to Fill scales the image until it covers the whole target box and trims whatever overhangs, so nothing is distorted but the edges are cut. Add Blank Space fits the entire image inside the box and pads the remainder, and for PNG that padding can stay fully transparent — or be filled with white, passport blue, black or a custom colour if you need an opaque result. Stretch forces the image to the exact dimensions and will visibly distort anything whose proportions do not already match.