Preview Power

Crop

Cropping refers to selecting a portion of an image you want to keep and eliminating everything outside the selection. When you open a non-PDF image in Preview, you can click and drag on the image to select a rectangular portion.

If you prefer to select a non-rectangular area, you can choose Elliptical, Lasso, or Smart Lasso selection tools from the Markup Toolbar. To reveal this secondary palette, click the marker tip on the toolbar or press Shift+Command+A (A is for Annotation, its name before Markup).

When you have the selection you want to keep, choose Tools > Crop, press Command+K, or click the Crop button on the Markup Toolbar.

To learn more about the selection tools, go to the Help menu, search for “selection,” and read the Annotate an image in Preview on Mac article.

Resize

If you have a non-PDF image and want to make it smaller, go to Tools > Adjust Size. You can specify Width and Height dimensions in pixels, various other units of measure, or as a percentage of the current size.

When you increase the dimensions of an image, it pixelates. That is, edges become rough, details are lost, and you can see the individual pixels that form the image. Therefore, you generally want to begin with a larger image and make it smaller for various purposes.

By default, the Image Dimensions area of the Adjust Size tool locks the proportions so the relative width and height are the same. However, you can toggle this by clicking the lock or (un)checking Scale proportionally. Then, you can adjust width and height independently and skew your image at will.

The third adjustable dimension in this area is Resolution, which refers to pixels per inch or pixels per centimeter. If you intend to increase resolution (some designers might require 300 ppi, for example), it’s best to decrease width and height by at least the same proportion to avoid pixelation. This happens automatically if you uncheck Resample image.

Convert

Some designers require images in a specific format. When designing for a website, it’s often good practice to keep image file sizes low, such as 100–200 kilobytes, so they don’t take long to load.

JPEG images are generally standard for websites but force a white background. PNGs can capture more detail and support transparency, but tend to result in larger files. When appropriate, you can also save an image as a TIFF, PDF, or various other formats.

To do so, choose File > Export… and choose your desired format in the Save dialog. For more choices, hold the Option key when you click the Format popup menu. Below the menu, you’ll see the approximate size of the new image file.