The Fastest Ways to Resize and Convert Images on Mac

Estimated read time 9 min read

Person using a MacBook on their lap at a coffee shop
Farknot Architect/

Your Mac comes with some powerful tools to make resizing and converting images fast and convenient. These include workflow tools like Automator and Shortcuts and Apple’s basic image viewer Preview.

Change the Size Manually With Preview

If creating Automator or Shortcuts workflows seems like too much hassle and all you want to do is resize a single image, Apple’s Preview app that comes with macOS can do what you’re looking for.

Any image file that will open in Preview can be resized with Preview. If you haven’t changed the default file associations for your Mac, double-clicking on an image file should open it in Preview (alternatively you can right-click then choose Open With > Preview).

With your file open, click Tools > Adjust Size at the top of the screen. You can choose from predefined sizes into which your image will sit, specify custom dimensions, or change the file resolution. You can also click on the “lock” icon to scale the vertical and horizontal axes independently, but be aware that this will skew the image.

Scale images with Preview for macOS

Once you’re done, hit Command+S to save your file.

RELATED: How to Create Custom Keyboard Shortcuts for Any Mac App

Resize Images to a Set Size With Automator

Let’s say you run a blog and you frequently convert images to a specific width or height. You could open an image editor every time you want to perform this action, or save time by using Automator to create a Quick Action that you can access from your right-click (two-finger click) menu instead.

To do this, launch Automator and choose “Quick Action” when prompted.

New Automator Quick Action

At the top of the workflow area, change “Workflow Receives Current” to “image files” and specify “Finder” as the application. Use the “Image” drop-down to select an icon you want to associate with the action, and customize the color if you want.

Specify image type in Automator workflow

Navigate to the “Finder” group on the left then click and drag “Get Specified Finder Items” into the main workflow menu.

Receive Finder input in Automator workflow

Now click on the “Photos” group and add the “Scale Images” action to your workflow. You’ll be asked if you want to add an action that saves a copy of your image before it is scaled, which you can do if you want. (We chose to skip it in our workflow).

Now specify the size you want either by pixel or percentage. If you pick pixels, keep in mind that applies to either axis. For example, if you specify 1200 pixels, a landscape image will be scaled to 1200 pixels wide, while a portrait image will be scaled to 1200 pixels high.

Scale Images with Automator workflow

Now hit Command+S to save your Quick Action. The name you choose is the label you’ll see in Finder, so make sure you’re happy with it.

You can now use your action by right-clicking (or two-finger clicking) an image file in Finder and then selecting “Quick Actions” followed by the workflow you just created.

Resize Images to a Custom Size with Automator

The beauty of the previous workflow lies in its one-click approach. You can select a lot of images and resize them all to a set size in virtually no time. But it’s also possible to create a simple Automator workflow that prompts you for a custom size, which requires one more step to execute.

First, follow the steps in the previous section and create the same workflow, then turn your attention to the “Scale Images” section. Click on “Options” and then make sure the box next to “Show this action when the workflow runs” is checked. This will tell macOS to ask for your input at this stage in the workflow.

Scale image and prompt for size in Automator

You can also specify a “default” size in the “Scale Image” section that will be pre-filled when you run the workflow. Now hit Command+S and give your workflow a name you’re happy with.

Now select an image (or group of images) in Finder, right-click and choose the workflow you just created under the “Quick Actions” section. You’ll be prompted to input a size when the workflow runs, after which your images will be resized.

Prompt for size in Automator when scaling images

Resize Images Using Shortcuts

Like Automator, Shortcuts can automate a huge variety of repetitive actions. Anecdotally speaking, it feels a little more sluggish than Automator but it’s a viable option if you don’t get along with Automator. You can also download a ready-made action and make changes to it.

To build an image resizing workflow, open Shortcuts and create a new blank workflow. To the right of the workflow click on the “Shortcut Details” icon (it looks like a set of sliders) then make sure “Use as Quick Action” and “Finder” is checked. If you leave “Services” checked and the action will appear in other apps like Safari too.

Get Input from Quick Actions in Shortcuts

Now take a look at the main workflow area. Change “Receive Any” to “Receive Images” so that the Shortcut only shows up when image files are selected.

Receive Images in Shortcuts

Now click on the “Action Library” button in the panel to the right of the workflow (it looks like a box with stars in it). Search for “resize” and drag the “Resize Image” action into the workflow window.

You can now choose between a predefined width or height (as specified by you), or you can opt to have the workflow prompt you every time for custom dimensions. If you want to be asked each time, right-click on the width field (it will read 640 by default) and choose Insert Variable > Ask Each Time. Do the same for the height if you want.

Ask Each Time for Resize in Shortcuts

If you go this route, “Auto Width” and “Auto Height” will apply where you supply no variable. So if you want to resize an image to 500 pixels tall, you can leave the “Width” prompt blank and simply enter “500” when prompted for the height. The Shortcut will scale the other axis accordingly.

Lastly, search for “save” and drag the “Save File” action into the workflow window. Hit the “Options” button to toggle “Ask Where to Save” off if you want to specify a specific location every time (like your Desktop folder).

Save resized image in Shortcuts workflow

Now double-click on the “New Shortcut” placeholder at the top of the window and give your workflow a name. You can also change the associated icon and color if you want.

You’ll now find your workflow under the “Quick Actions” right-click menu when an image file is selected. You can click on the Share button and copy a link to your workflow and share it with friends. Click here to download the above workflow.

Get prompted for an image size in Shortcuts workflow

Build a “Convert to JPEG” or Similar Quick Action

macOS already includes a “Convert Image” Quick Action which you can enable under System Preferences (System Settings) > Extensions > Finder, which prompts you for an image type and general size when converting an image.

But if you want a faster way of converting an image to a specific type (like JPEG), you can create an Automator workflow to do that. This works great for converting HEIC images shot on an iPhone to a full-sized JPEG with minimal fuss.

Open Automator and select Quick Action when prompted. At the top of the workflow make sure “image files” and “Finder” are selected in the respective drop-down box. You can also customize the icon and color if you want.

Specify image type in Automator workflow

Under the “Finder” group in the actions library, drag “Copy Finder Items” to the main workflow area. You can either specify a location or use the “Show this action when the workflow runs” toggle under “Options” if you’d rather be prompted every time.

Copy Finder Items in Automator

Navigate to the “Photos” group in the actions library and drag “Change Type of Images” to the workflow area. Specify the image type you’d like to use, we’re using JPEG here.

Change Image Type in Automator workflow

Now hit Command+S and save your Quick Action with a suitable label. You’ll now find it under the “Quick Actions” menu when you right-click an image file inside Finder. Since we’re copying the file, your original image won’t be affected.

RELATED: How to Quickly Batch Rename Files on Windows, Mac OS X, or Linux

Convert a PDF to Images with One Click

If you want to convert all pages within a PDF to images quickly, you can do so with a Quick Action. First, launch Automator and make sure “Workflow receives current” points to “PDF Files” and that “Finder” is selected in the applications drop-down. Give your workflow a suitable icon and a color if you want.

Automator workflow receives PDF files in Finder

Under the “PDFs” group in the action library, drag “Render PDF Pages as Images” into the main workflow window. Specify the image type, resolution, and compression level to use.

Options when rendering PDF as Images

Navigate to the “Finder” group in the actions library and drag “Move Finder Items” into the workflow window. This will save the resulting images in the location you specify, or you can enable “Show This Action When Workflow Runs” under “Options” to be prompted every time.

Move Finder Items action to save images in Automator workflow

Hit Command+S and save your workflow, giving it a label like “Convert PDF to Images” and it will appear under the “Quick Actions” menu when you right-click (or two-finger click) a PDF file in Finder.

Customizing Quick Actions

You can add and remove Quick Actions under System Preferences (System Settings) > Extensions > Finder. To remove something that you don’t find helpful, uncheck it. You can also reorder how your Quick Actions appear by clicking and dragging them.

Customize Quick Actions in macOS System Preferences

Quick Actions you have created will be stored in the ~/Library/Services/ folder, which you can access by launching Finder and then clicking Go > Go to Folder at the top of the screen. Double-clicking an action will open it in Automator, so you can make changes.

Renaming a Quick Action in this folder doesn’t always result in the label changing under the Quick Actions menu, so you may need to copy and paste the steps into a new Quick Action and then delete the old one if you want to change its name.

Do More With Shortcuts

Automator may seem intimidating to start with, but it’s a powerful tool that’s well worth exploring. Hopefully, the workflows above will help you create your own time-saving automations.

Shortcuts is another app that can help save you time. Check out (and download) some of our favorite macOS Shortcuts workflows.

RELATED: 8 Mac Shortcuts Actions You’ll Actually Use

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