Use the preview app to reduce multiple images at once on a Mac

Convert photos in the preview app
Convert photos in the preview app
Convert photos in the preview app

Today I once again had an interesting question from a reader: She had problems with software that only allows photos in a certain maximum size. There are many reasons why you want to calculate photos or images smaller on the Mac - saving memory, adjustments to a web-compatible size or similar can be the reason. There are also plenty of tools for this that cost more or less money and provide a batch resize function. But I wanted to see if you couldn't do it with on-board tools from macOS and was asked with the built-in previewApp of the Mac operating system. This software really has more talents than one would like to think. And as a little treat, the preview app calculates not only JPEGs but also PNG graphics smaller.

The procedure step by step

Here are the individual steps in detail on how to reduce the size of the images in the “Preview” program:

  1. since the process will directly overwrite the original images, I recommend that you make a backup of the graphics
  2. marked in Finder the photos you want to convert (you can select multiple files by holding down the cmd key)
  3. either double-click the selected files or right-click (or control-click) the files and then select "Open With" and then click "Preview.app" from the submenu
  4. now all photos are open in “Preview” and you mark them all in the left bar (keyboard shortcut cmd + A does the same)
  5. At the top of the menu there is the item "Tools" and in it the function "Resize"... you select this
  6. Now a window opens in which you can make various settings. I recommend keeping the proportional change and changing the dimensions to "pixels"... now you can enter your desired pixel dimensions and below you'll get a preview of how the file size will change
  7. Click on OK if you are satisfied (but be careful! The preview will IMMEDIATELY overwrite the files and DO NOT save them as new files!)
  8. if you want to start all over again, you can cancel the action with the keyboard shortcut cmd + Z and try again ;-)

Zooming out with the preview app explained in screenshots

Here I have documented the process for you using screenshots. Maybe this will help you to understand the individual steps. You can also click on the screenshots to see them larger.

Via the context menu, click "Open with" to call up all selected images in the preview app.
All marked images in the preview app can be called up via the context menu via “Open with”.
The images in the preview must all be marked: The keyboard shortcut CMD + A does this job.
The images in the preview must all be marked: The keyboard shortcut CMD + A does this job.
Under "Tools" -> "Size Correction" you call up the dialog window via which the new image sizes can be set.
Under "Tools" -> "Size correction" you call up the dialog window in which the new image sizes can be set.
Here you can see the window in which you can make the appropriate settings for the size conversion.
Here you can see the window in which you can make the appropriate settings for the size conversion.
The info window in the preview app shows whether the resizing worked.
The info window in the preview app shows whether the resizing worked.

I hope the contribution helps you with the conversion and saves a few euros. You don't always have to shoot pictures with Photoshop. Sometimes a small, free tool from Apple will do the graphics jobs too. ;-)

If the contribution helped you, I would be happy if you would share it on the social networks. Thanks!

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11 Response to “Resize multiple images at once on Mac using the Preview app”

  1. Wow, thanks for this tip! It makes life easier for you. Am thrilled! Do you also have a tip on how to rename several pictures at the same time? So give them all the same name, maybe numbered?

    1. Hello Katy! Yes, you can even do this with the Finder without any extra tools. You mark all the files that you want to rename and then click with the right mouse button (or with CTRL + mouse button) on the files and then select the item “x objects rename”. Then comes a small menu in which you can set the procedure for renaming the files. :)

  2. Hello Sir Apfelot,
    Thank you for the tip.
    However, I am looking for a program that is equivalent to the Paint program on the IMac. For example, to briefly mark something, to incorporate a circle or an arrow. Which program were used to process the photos shown above?
    Thank you for a tip.
    Regards

    1. Hello Dirk! Oh, you don't need a special program for that. I always do that with Apple Mail! :) You drag a screenshot into a new mail, then click on the arrow in the upper right corner of the image in the mail and select "Marking". Now the screenshot will open in a mini editing tool that you can use to add arrows, circles, ellipses and text. When you're done, you close it and you'll have the revised version in the mail. I then simply drag this onto the Photoshop symbol and export it as a JPG or PNG. But you can also copy and paste it into any other program. I'm going to write a little guide about it these days, because it's really 10x better than all the programs that you can buy especially for this purpose. Apple Mail is my favorite secret weapon... and it's free!

      1. Moin,

        First of all, thanks for the great tip Sir Apfelot.
        A little hint for quick markup: Open the image in Preview, go to Tools and then select “Annotate”. There you can easily and quickly insert text, arrows, etc.

        Greetings from China ^^

  3. Hello!
    I've had a storage problem since shrinking my photos. I have now gained 20 Gb in the folder with my images. All in all, however, I was suddenly shown 20 Gb less on the computer. I restarted and am back to the space I had before shrinking. So from 37 down to 19, back to 37. I can see the 20 Gb less in the folder information, but not generally on the computer. I thought there were cache files or duplicates somewhere, but CleanMyMac didn't find anything. What can I do now?
    Thank you very much
    Agnès

    1. Hello Agnes! Actually, CleanMyMac should clean everything that concerns caches. How did you "resize" your photos? Perhaps this is where the problem lies and the originals are still somewhere?

  4. Hi Jens,

    that's basically how I do it. Only in the last step I export the scaled down files to a subfolder instead of overwriting the large ones.

    This way I keep the originals and have the other size copies in a subfolder.

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