How to batch resize your image collection using Preview in macOS

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in macOS
If you have a large collection of images that you need to resize, an easy way to change all of the files quickly is to use Preview, included within macOS, instead of using a dedicated utility or an image editing program's functions. AppleInsider walks through how to batch process the photographs and other graphics to fit a certain size.

resize images preview macos batch photos


Photographers and other people who spend time amassing large collections of images typically are not concerned about the dimensions of each file. For most purposes, having the file in as high a quality and resolution as possible is preferred, unless users have severe concerns about how much free storage they have available on their local drives.

There are, however, situations where it is a good idea to try to make changes to such collections. For example, if a number of photographs are being hosted on a website or emailed to someone, the file size could be an issue. Reducing the number of pixels and making all images a uniform size is also useful in some applications.

Some image editing suites offer batch processing functions, but it is also available from the macOS desktop, using the built-in Preview app's basic editing tools.

Opening All Images

To start the process, you need to open all of the images in a single Preview instance. The easiest way to do this, if all the image files are in the same folder, is to select all of them, right-click, select Open With then Preview.

  • resize images preview macos batch photos
  • resize images preview macos batch photos
  • resize images preview macos batch photos


This will open one Preview window with an extra column on the left-hand side, showing all of the images included in the folder. You can scroll up and down this column, clicking to view individual files in the main panel.

Confining the Image

Within Preview's menu bar, select Edit, then Select All, to highlight all of the image files in the app. You can also drag to highlight files using the mouse if you wish to change individual or smaller groups of files.

  • resize images preview macos batch photos
  • resize images preview macos batch photos


With all required images selected, click Tools then Adjust Size... in the menu bar. This will bring up a new window, which will ask to set various properties regarding size to the selecting images.

resize images preview macos batch photos


It is possible to select a dimension in the Fit Into dropdown box if you need to use a common size. On clicking OK, this will resize all of the images down or up so it can fit within the bounds of the selected resolution.

If you wish to change to a specific height or width, click in either box and type in the required measurement, while leaving the other box blank, then click OK. This will make all images have the same width or height, scaling the other dimension up or down to achieve the required measurement.

The Scale proportionally box should remain ticked, otherwise this could distort the images. It is also suggested to have Resample image ticked as well.

At the bottom of the window, the Resulting Size box will advise of what will happen to the images once OK is clicked, from a file size perspective. This could be handy to look at when selecting different resolutions, if the file size of the entire collection plays a factor in your choices.

  • resize images preview macos batch photos
  • resize images preview macos batch photos


Once changes have been made, save the files using the menu.

resize images preview macos batch photos


When quitting Preview, it will also bring up a confirmation box offering to revert an image back to its original state or to save it. Notably, this comes up for each and every image used in this way and cannot be skipped, so the quickest way through is to repeatedly tap enter on the keyboard to save each item.

resize images preview macos batch photos

Further Notes

The mass-editing works for a few other options in Preview, including rotating and flipping images. Not everything works in this way, such as annotations which are performed on a per-image basis.

  • resize images preview macos batch photos
  • resize images preview macos batch photos



As the final "revert changes" confirmation box appears for every image edited, this can be a nuisance for cases where extremely large image collections need editing. In such cases, it may be worth exploring using similar functions in image editing suites instead of using this technique.
Alex1N

Comments

  • Reply 1 of 12
    cashxxcashxx Posts: 100member
    Automator!
    Alex1N
  • Reply 2 of 12
    boltsfan17boltsfan17 Posts: 2,013member
    cashxx said:
    Automator!
    I use that as well to batch convert RAW to JPEG. 
    Alex1N
  • Reply 3 of 12
    macxpressmacxpress Posts: 4,576member
    cashxx said:
    Automator!
    Ugh...Automator. The most unintuitive app I've ever seen come out of Apple. All that app does is piss me off. 
  • Reply 4 of 12
    dysamoriadysamoria Posts: 1,812member
    That's odd. I've tried to do this with "Adjust Color" and it didn't do anything to any but the first image.
  • Reply 5 of 12
    MacProMacPro Posts: 17,562member
    Great tip, must try this as I am guessing Preview isn't opening them all really just opening thumbnails at left thus not hogging RAM.
  • Reply 6 of 12
    If someone can convert RAW to JPED inside of Photos I'd be interested. 
  • Reply 7 of 12
    Mike WuertheleMike Wuerthele Posts: 3,302administrator
    dysamoria said:
    That's odd. I've tried to do this with "Adjust Color" and it didn't do anything to any but the first image.
    I don't think adjust color will do them all. For sure, you can batch resize -- like the tip demonstrates.
    Alex1N
  • Reply 8 of 12
    lorin schultzlorin schultz Posts: 2,090member
    How do the results look, compared to a dedicated imaging app like Photoshop or Pixelmator? Adobe used to make some noise about how their resizing algorithm resulted in better-looking reductions with fewer artifacts. In fact, they even let you choose from more than one method.

    If one wants to resize without buying a dedicated app, wouldn't Photos be safer? That way you can restore the original size if you ever need to. Does it allow batches?
  • Reply 9 of 12
    ivanhivanh Posts: 208member
    I have hundreds of rolls of 135mm films scanned and now being stored in the Photo app library.  They are aged and yellowish. How can their original colour be restored and the creation dates be fixed back to the photo dates? Any advice?
  • Reply 10 of 12
    laytechlaytech Posts: 111member
    Like others, I use Automator and yes, it is not very intuitive, but I managed to create a context menu item that is simply called resize, so I just select all my images, right click and go to my new menu item resize and it works fantastic. I also have standalone automator feature that I just drag images into and it resizes them.

    Automator is great but it does take some figuring out. However, good to know about Preview feature because I was not aware it would re-size. 

    If Apple is to improve any application it has to me mail, why does Apple Mail send about 5 useless attachments to Outlook recipients with just a basic text email? Hopeless and it effectively stops me using mail for everyday use. (just slightly digressing there)
  • Reply 11 of 12
    fastasleepfastasleep Posts: 1,786member
    MacPro said:
    Great tip, must try this as I am guessing Preview isn't opening them all really just opening thumbnails at left thus not hogging RAM.
    Why would you assume that? Also why would you assume it's going to be "hogging" RAM?
  • Reply 12 of 12
    jhakjhak Posts: 1member
    If you do not wish the "confirm changes" box to appear for every image, as long as the conversions are complete,(you can see this when there are no more thumbnails shown as 'selected') simply do a cmd Q to exit Preview, and a single confirm is all that's needed.
    A possible down side to this is that the original images are copied into: /private/var/folders/qv/blah, blah/T/com.apple.Preview/blah blah
    these will have to be manually deleted if ,like me, you're after saving a bit of disk space
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