Resizing is the single biggest saving for most images. A photo shown 1200 pixels wide does not need to be 4000 pixels wide. Here is how to resize many at once on a Mac.
Preview: resize a batch to exact dimensions
- Select all the images in Finder and open them together in Preview.
- In Preview’s sidebar, select every thumbnail (⌘A).
- Choose Tools › Adjust Size.
- Enter a width or height, keep Scale proportionally on, and click OK.
- Choose File › Save. Preview overwrites the originals, so work on copies.
Finder: quick sizes, no precision
Select images, Control-click, and choose Quick Actions › Convert Image. Choose Small, Medium or Large. You cannot set exact pixel sizes, but the originals are kept.
Terminal: sips
To make the longest side of every JPEG in a folder at most 1600 pixels:
sips -Z 1600 *.jpg
This also overwrites the originals. Copy the folder first.
The problem with batch cropping
Resizing keeps the whole picture. Cropping to a fixed shape, such as square thumbnails, is harder: a centred crop cuts off heads and products that sit off-centre, and the built-in tools do not let you fix one photo without redoing them all.
With Shrinker Studio
- Drop the images into Studio.
- Add the Resize & crop step and set the size. For crops, choose subject-aware placement, which keeps the subject of each photo in frame.
- For any photo where the crop is not right, place it by hand. Only that photo changes.
- Need several sizes for a website? Add Responsive set to export each photo at multiple widths, with the srcset snippet ready to paste.
- Press Export. Originals are never touched unless you choose to replace them.