Image Compression Basics: Quality, Size and Format
There are two main levers: fewer pixels (dimensions) and less information per pixel (quality/codec). For most web images, cap the longest side first, then adjust quality; do not crush screenshots and text. Format controls transparency, compatibility and efficiency rather than simply being smaller.
Dimensions first, quality second
A longest side of 1600-2000px is usually enough for web images.
Avatars and thumbnails only need 256-512px; do not ship the original.
After resizing, 80-85% quality is often visually sufficient.
Choose by content
Photos and gradients: JPEG or WebP.
Transparency, icons and text screenshots: PNG or WebP.
Old software compatibility: JPEG or PNG.
FAQ
Does compression lose quality?
JPEG/WebP are lossy and PNG is lossless; resizing also loses detail. Keep the original.
Why is the result larger?
The output format/settings may not fit, or the original is already optimized; try WebP or smaller dimensions.
Sources
Related calculators
Image CompressorChoose a JPG/PNG/WebP, set quality and max width, compress locally and compare before/after size for uploads, email and web images.More guides
Compression Settings for Email, Web and UploadsRead guide继续读
按顺序读，或跳到同主题的其他指南。