How this works
This shrinks pixel dimensions directly — either to a percentage scale or to fit within a maximum width/height box — which is a different lever from Compress Image, which keeps dimensions the same and only lowers encoding quality. Use this when the file itself is too large in pixels, not just too heavy in bytes.
Common questions
What's the difference between this and Compress Image?
This changes the actual pixel dimensions; Compress Image keeps the same dimensions and just re-encodes at lower quality. Reducing resolution usually saves more file size for photos that are much bigger than they need to be displayed.
Can this make an image bigger?
No — it never upscales, only ever shrinks or leaves the image the same size.