How Image Compression Works

Compression changes how image information is represented. Lossless methods preserve the information needed to reconstruct the same image data, while lossy methods discard some information to achieve smaller files.

Compression vs resizing

Compression changes encoding. Resizing changes the number of pixels. For a very large camera photo, reducing dimensions can have a larger effect on file size than quality reduction alone.

Lossy and lossless

PNG is commonly used as a lossless format. JPG is commonly lossy. WebP can support both lossless and lossy modes depending on how it is encoded.

Choose by use case

Keep a high-quality source copy. Create smaller derivatives for websites, email or sharing rather than repeatedly recompressing the only original.