Resizing changes pixel dimensions
An image's dimensions describe its width and height in pixels. Resizing changes those dimensions. If an image is displayed at a smaller size than its original, reducing its pixel dimensions can remove data that the display does not need.
The shrinkpixel resize tool fits an image within the maximum width and height you set, keeps the aspect ratio, and does not enlarge a smaller image.
Compression changes how image data is encoded
Compression changes how the pixels are stored in a file. Lossy formats such as JPEG can discard some image information to reduce bytes. PNG uses lossless compression, while WebP can be encoded with lossy or lossless compression depending on the encoder.
Reducing dimensions and changing the encoding are different operations. A smaller image can still have a large file if it uses a format or settings that store the image inefficiently.
Which should you use?
- Resize when you know the image will be displayed or uploaded at smaller pixel dimensions, or when an upload form requires maximum dimensions.
- Compress when the dimensions are suitable but the file takes too many bytes to store or send.
- Use both when the image is larger in pixels than needed and also needs a smaller file size. Review the final dimensions, file size, and visual quality.