Change Images preferences in Preview on Mac
On your Mac, use Images preferences in Preview to change whether a selection of files opens in individual windows or one Preview window. You can also set the scale of images so that one pixel in a document equals one screen pixel or set the size of the image onscreen to be the size of the image when printed.
To change these preferences, choose Preview > Preferences, then click Images.
When opening files
After you select multiple image files, you can have Preview open them in a single window or in individual windows. To view all files in one window, click “Open all files in one window.” To view each file in a separate window, click “Open each file in its own window.” To open groups of image file types together in one window, click “Open groups of files in the same window.”
Define 100% scale as
Set how an image appears onscreen or when printed by setting the scaling option. To display an image at full resolution of one image pixel equaling one screen pixel, click “1 image pixel equals 1 screen pixel.” To set the print size of an image to be the size that appears onscreen, click “Size on screen equals size on printout.”