Do you work with a lot of images at one time? Maybe you have a large group of images you need to resize to a consistent size and convert from PNG to JPG. Instead of changing each image separately, there are easy ways to quickly batch convert and resize images on your Mac.
Below, we look at using the built-in tools in Preview and Automator to batch convert and resize images. We’ll also introduce a couple of third-party apps that will do the trick with some extra features thrown in.
For this guide, we’ll combine converting and resizing. But you can also do each separately on your batch of images.
Batch Convert and Resize Images Using Preview
In Finder, select a group of image files, and right-click on them. Go to Open With > Preview. If you have the Preview icon on your Dock, you can also drag the selected files onto the Preview icon to open them. From there:
- Click in the left pane then press Cmd + A, or click Edit > Select All from the menu bar to select all the images.
- Select Tools > Adjust Size from the menu bar.
- Choose the units you want to use (pixels, percent, inches, cm, mm, or points) from the dropdown box to the right of the Width and Height fields.
- If you want the Height to adjust automatically when you enter the Width, or vice versa, make sure to check the Scale proportionally box.
- Enter values for one or both the Width and Height and click OK.
- Note that if your images are all different sizes, you may want to use percent, because it’s relative to the original size.
Now, let’s convert the images. Batch image conversion in Preview works with almost all image formats, including GIF, JPEG, JPEG-2000, BMP, Photoshop PSD, PNG, TIFF, and even PDF. You can convert any number of image files using this.
To start converting in Preview:
- Make sure all the images are still selected and go to File > Export Selected Images.
- Navigate to the folder where you want to save the images and click Options to reveal the Format dropdown list.
- Select the desired format, optionally adjust the available settings, and click Choose.
Batch Convert and Resize Images Using Automator
Automator is a powerful, built-in utility on your Mac that allows you to create custom automation apps without knowing any coding. Don’t be intimidated by Automator—it’s easy to use.
To start a new Automator document:
- Open Automator from your Applications folder (or search for it using Spotlight with Cmd + Space) and click New Document.
- On the Choose a type for your document dialog box, click Application and then hit Choose.
There are two main sections on the Automator window: Actions and Variables are on the left, while the workflow is on the right. The process of building an Automator workflow involves selecting the type of Action or Variable you want and then dragging it into your workflow.
In essence, you’re building a step-by-step process that tells Automator what to do with the files you give it.
Create a New Folder
First, we’re going to have Automator create a folder to place the converted and resized images into.
Make sure Actions is selected right under the toolbar. Select Files & Folders under Library on the left. Next, find the New Folder action in the second column and drag it to the workflow on the right. After this, the New Folder action is put in place at the beginning of the workflow, with some options on the action box.
Enter a name for the new folder in the Name box. By default, this new folder will be created on the Desktop, but you can choose another location using the Where dropdown list.
Get the Images
So far, we’ve told Automator to take the images you drag onto the app icon and copy them to the new folder. Now, we need to tell Automator to select the images to modify.
Under Library, select Files & Folders. Next, drag the Get Folder Contents action to the bottom of the workflow.
Convert the Images
The next step is to tell Automator to convert the images. Under Library, select Photos, and then drag the Change Type of Images action to the bottom of the workflow.
A dialog displays asking if you’d like to add a Copy Finder Items action to the workflow so the image files will be copied, preserving your original files.
Because we added an action to the workflow that will create a new folder, we don’t need to make copies of the original files. The New Folder action will take care of that. So click Don’t Add on the dialog box.
On the Change Type of Images action box in the workflow, select your desired image format from the To Type dropdown list. This will take the images you’ve added using the Get Folder Contents action and convert them to the selected image format.
Resize the Images
If you also want to resize your images, you can add an action that will scale them all. Under Library, select Photos. Next, drag the Scale Images action to the bottom of the workflow.
Select whether you want to convert the images to a specific size in pixels or using a percentage from the dropdown list. Enter the number in pixels or the percentage in the box. As mentioned earlier, if you’re working with images of various sizes, you may want to use By Percentage as it works relative to the original size.
You’ll be asked again if you’d like to add a Copy Finder Items action to the workflow to make a copy of the original files. Again, click Don’t Add.
Save the Application and Add It to Your Dock
We’re finished creating our workflow. Now, it’s time to save it as an app. Go to File > Save. Navigate to where you want to save your app and enter a name for the app in the Save As box at the top of the dialog box. Next, click Save.
Finally, drag the Automator app file you just saved to the Dock for easy access.
Convert and/or Resize the Images
To convert and resize a batch of images, select the image files and drag them onto the app icon on the Dock.
Depending on the number and size of the selected images and the speed of your Mac, after a few seconds or minutes, you’ll have a new folder on your Desktop containing the converted and resized images. This preserves the original files, so you don’t have to worry about any irreversible changes.
Batch Convert and Resize Images Using a Third-Party App
There are also third-party apps you can install on your Mac to convert and resize your images. Here are a couple for you to consider.
XnConvert is a free program that makes it easy to batch convert and resize images. In addition, it can perform many other actions on images, like rotating/cropping and adjusting the brightness, contrast, and saturation. You can also use it to apply blur, emboss, and sharpen filters, or add masking and watermarking effects.
Add your images on the Input tab. Next, add an action on the Actions tab to resize the image by pixels, percent, inches, cm, or mm and specify the Width and Height values.
On the Output tab, select the folder for the converted files and choose a format you want to convert to. You can also customize the file names and adjust some other options.
When you’re ready to convert your images, click Convert.
Download: XnConvert (Free)
With ImageSize, you can batch resize, convert, and rename your image files and keep the original aspect ratio from them. You can resize images by pixels, percent, or fixed width or height. Input and output formats include the most popular types like JPG, JPEG, PNG, TIFF, GFT, BMP, and more.
Add your images on the ImageSize window and set the resize options on the Resize tab on the right. Then click the Output tab, pick the image Format you want, and select the Output Folder.
Click Resize Images on the Output tab to resize and convert your images and save them to the selected folder.
Download: ImageSize ($3.99)