What determines perceived quality
Resolution sets the ceiling. Enough pixels must be present to resolve the detail you expect, or the image will look soft no matter how gently it was compressed.
Compression sets how much of that ceiling survives. Aggressive lossy settings blur fine texture and introduce ringing around edges, while thoughtful settings preserve faces and text even at small sizes.
Quality versus file size
The two pull against each other: more retained detail means more bytes. The practical art is finding the lowest size where the image still looks right where it will be shown.
Display size changes the answer. A photo shown at 600 pixels wide hides flaws that would be obvious at full resolution, which is why heavy compression often goes unnoticed on the web.
- Check the image at its final display size
- Reduce dimensions before pushing compression hard
- Watch for blocky edges and smeared text
- Keep a high-quality master for future edits
Keeping quality while shrinking files
Compress once from the best available original. Repeated saves accumulate damage, so start from the master rather than from an already shared copy.
Filekind compresses to a chosen limit and shows the resulting size and dimensions before download, letting you judge the trade in the browser. Inputs up to 25 MB and 48 megapixels are supported.