如何正确使用质量滑块，不毁掉图片细节

Bottom line: Quality is not a universal unit. A value of 75 in one AVIF encoder does not mean exactly the same visual quality as 75 in a JPEG encoder. Treat the slider as an encoder-specific control and judge the output visually rather than assuming a number is portable.

Start with the intended display size. A hero image displayed at 1600 pixels wide does not need an 8000-pixel source. Resizing first often saves far more than fine-tuning quality. Then choose a moderate setting—roughly 70–82 for WebP or AVIF—and inspect hair, fabric, small text and gradients.

Watch for distinct artifacts. JPEG creates blocking and ringing around edges; WebP and AVIF can smooth fine texture or introduce banding. If the picture looks painterly or faces lose skin texture, increase quality. If the file remains large but looks perfect, reduce quality in small steps.

Screenshots need different rules. Text and interface edges should remain crisp, so lossless PNG is often better. If a screenshot is mostly photographic, a lossy format can work, but test the smallest text on mobile before publishing.

A good compression UI should show input size, output size, percentage saved and a thumbnail. That immediate feedback prevents two common mistakes: over-compressing to hit a number and re-encoding already compressed originals until visible damage accumulates.