Resizing photos is a fundamental skill for anyone working with digital images, whether you’re a professional photographer, a social media enthusiast, or simply someone who wants to share pictures with friends and family. Large image files can take up valuable storage space, slow down website loading times, and be difficult to share via email or messaging apps. Fortunately, macOS provides several built-in tools and readily available apps that make resizing photos quick and easy. This comprehensive guide will walk you through various methods to resize photos on your Mac, catering to different needs and skill levels.
Why Resize Photos?
Before diving into the how-to, let’s briefly discuss why resizing photos is important:
- Saving Storage Space: High-resolution images consume a significant amount of storage. Resizing reduces the file size, freeing up valuable space on your Mac’s hard drive or external storage devices.
- Faster Website Loading Times: Large images can significantly slow down website loading speeds. Resizing images before uploading them to your website improves user experience and search engine optimization (SEO).
- Easier Sharing: Large image files can be difficult to share via email, messaging apps, or social media platforms. Resizing makes them more manageable and easier to send.
- Optimized for Different Uses: Different platforms and devices require different image sizes. Resizing allows you to optimize images for specific purposes, such as website banners, social media posts, or printed materials.
Methods for Resizing Photos on Mac
macOS offers several built-in tools for resizing photos, as well as a variety of third-party apps that provide more advanced features. Here’s a breakdown of the most common methods:
1. Using Preview (The Built-in Image Viewer)
Preview is the default image viewer on macOS and provides a simple and effective way to resize photos without installing any additional software. Here’s how to do it:
- Open the Image in Preview: Locate the image you want to resize in Finder. Double-click the image file. It should automatically open in Preview. If Preview is not the default image viewer, right-click the image, select “Open With,” and then choose “Preview.”
- Access the Adjust Size Tool: Once the image is open in Preview, go to the menu bar at the top of the screen and click on “Tools.” From the dropdown menu, select “Adjust Size…”
- Enter New Dimensions: The “Adjust Size” window will appear. Here, you can enter the desired width and height for the resized image.
- Pixels: The default unit is pixels (px). You can change this to inches, centimeters, millimeters, or percent using the dropdown menu next to the width and height fields.
- Constrain Proportions: Make sure the “Scale proportionally” checkbox is selected. This maintains the original aspect ratio of the image, preventing distortion. If you want to change the aspect ratio (e.g., to crop the image), uncheck this box, but be aware that this can make the image look stretched or squashed.
- Fit into: You can also choose from preset sizes such as Small, Medium, Large, or Custom. This is useful if you need to quickly resize an image to a common size.
- Resolution (DPI): The “Resolution” field determines the number of pixels per inch (DPI) in the image. A higher DPI generally results in a sharper image, but also a larger file size. For web use, a resolution of 72 DPI is usually sufficient. For printing, a resolution of 300 DPI is recommended. Adjust the resolution as needed.
- Resample Image: The “Resample image” checkbox tells Preview to actually change the pixel data of the image to fit the new dimensions. Make sure this box is checked.
- Click “OK”: Once you’ve entered the desired dimensions and resolution, click the “OK” button. Preview will resize the image.
- Save the Resized Image: Go to “File” > “Save” or “File” > “Export…” to save the resized image.
- Save: If you choose “Save”, Preview will overwrite the original image with the resized version. Caution: This is generally not recommended, as you may want to keep the original, high-resolution image.
- Export: Choosing “Export…” allows you to save the resized image as a new file with a different name and format. This is the recommended option. In the Export window, you can choose the file format (JPEG, PNG, TIFF, etc.), adjust the quality (for JPEG), and specify the file name and location.
- Quality (JPEG): If you’re saving as a JPEG, use the Quality slider to adjust the level of compression. Lower quality settings result in smaller file sizes but can also introduce noticeable artifacts (pixelation). Experiment with different quality settings to find a balance between file size and image quality. Generally, a quality setting of 60-80% is a good starting point for web use.
Pro Tip: For quick resizing to commonly used sizes, explore the “Fit into” option in the “Adjust Size” window. You can select “Small,” “Medium,” or “Large” to quickly resize the image to predefined dimensions.
2. Using Photos App
The Photos app, Apple’s default photo management application, offers another way to resize photos, although it’s less direct than Preview. The Photos app primarily focuses on managing and organizing your photo library, but it does have basic editing capabilities, including export options that allow you to control the size of the exported file.
- Open the Image in Photos: Open the Photos app and locate the image you want to resize. If the image is not already in your Photos library, import it by dragging the image file into the Photos window or by going to “File” > “Import” and selecting the image file.
- Select the Image: Click on the image to select it.
- Export the Image: Go to “File” > “Export” > “Export [Number] Photo(s)”.
- Choose Export Settings: In the Export window, you’ll see several options for controlling the size and quality of the exported image.
- Photo Kind: You can choose between “JPEG,” “PNG,” “TIFF,” and “Original.” Choose “JPEG” for the best balance between file size and image quality for most purposes. “PNG” is suitable for images with transparency or graphics with sharp lines and text. “TIFF” is a lossless format that preserves image quality but results in larger file sizes. Choosing “Original” exports the image without any modifications, maintaining its original size and format.
- Quality (JPEG only): If you choose “JPEG,” you can adjust the quality using a slider. Lower quality settings result in smaller file sizes but can also introduce artifacts. Experiment to find a good balance.
- Size: This is where you control the size of the exported image. You have the following options:
- Small: Exports the image at a smaller size, typically suitable for email or small web thumbnails.
- Medium: Exports the image at a medium size, suitable for general web use.
- Large: Exports the image at a larger size, suitable for printing or displaying on larger screens.
- Actual Size: Exports the image at its original size.
- Custom: This option allows you to specify the maximum dimensions (width or height) of the exported image. Enter the desired maximum dimension, and Photos will automatically scale the image to fit within those bounds while maintaining the aspect ratio. This is the most precise way to resize images in Photos.
- Specify File Name and Location: Choose a file name and location for the exported image.
- Click “Export”: Click the “Export” button to export the resized image.
Note: The Photos app focuses on relative size adjustments rather than precise pixel dimensions (except for the custom option). It’s best suited for quick resizing when you don’t need to specify exact width and height values.
3. Using Automator (For Batch Resizing)
Automator is a powerful built-in macOS application that allows you to automate repetitive tasks. You can use Automator to create a workflow that resizes multiple images at once, saving you time and effort. This is particularly useful if you need to resize a large batch of photos for a website or other project.
- Open Automator: Launch Automator from the Applications folder (or search for it using Spotlight).
- Choose a Document Type: When Automator opens, it will ask you to choose a document type. Select “Quick Action” and click “Choose.”
- Configure the Quick Action: In the Automator window, configure the Quick Action as follows:
- Workflow receives current: Change this to “image files” in “Finder.”
- Search for Actions: In the search box on the left side of the window, type “Scale Images.”
- Add the “Scale Images” Action: Drag the “Scale Images” action from the list of results to the workflow area on the right.
- Set the Resizing Options: In the “Scale Images” action, you can specify the resizing options.
- By Percentage: You can scale the images by a percentage of their original size. For example, entering 50% will reduce the width and height to half of their original values.
- To Size: You can specify the maximum width or height of the resized images. Automator will automatically scale the images to fit within these bounds while maintaining the aspect ratio.
- Add the “Rename Finder Items” Action (Optional): If you want to rename the resized images, add the “Rename Finder Items” action to the workflow after the “Scale Images” action. This is useful for adding a suffix to the file names to distinguish them from the original images.
- Save the Quick Action: Go to “File” > “Save” and give your Quick Action a descriptive name, such as “Resize Images.” Automator will save the Quick Action to the Services menu.
Using the Quick Action:
- Select the Images: In Finder, select the image files you want to resize.
- Run the Quick Action: Right-click on the selected images and choose “Services” from the context menu. Then, select the name of your Quick Action (e.g., “Resize Images”).
- Automator will process the images: Automator will automatically resize the images according to the settings you specified in the workflow. By default, Automator will save the resized images in the same folder as the original images. You can change this behavior by adding the “Copy Finder Items” action to the workflow before the “Scale Images” action.
Important Considerations for Automator:
- Backup Your Images: It’s always a good idea to back up your original images before using Automator to resize them. This way, if anything goes wrong, you can easily restore the original versions.
- Test the Workflow: Before running the Quick Action on a large batch of images, test it on a small sample of images to make sure it’s working as expected.
4. Using Third-Party Apps
While macOS’s built-in tools are sufficient for basic resizing tasks, third-party apps offer more advanced features and control over the resizing process. Some popular options include:
- Adobe Photoshop: Photoshop is the industry-standard image editing software and provides a comprehensive set of tools for resizing, cropping, and manipulating images. It offers precise control over dimensions, resolution, and resampling methods.
- GIMP (GNU Image Manipulation Program): GIMP is a free and open-source image editor that provides many of the same features as Photoshop. It’s a great option for users who need advanced image editing capabilities but don’t want to pay for Photoshop.
- Affinity Photo: Affinity Photo is a professional-grade image editor that offers a powerful and affordable alternative to Photoshop. It provides a wide range of tools for resizing, retouching, and enhancing images.
- iMazing HEIC Converter: While primarily designed to convert HEIC images to JPG, iMazing HEIC Converter also provides options to resize images during the conversion process. This is useful if you need to convert HEIC images (the default format for photos taken on iPhones) to a more widely compatible format like JPG while also reducing their file size.
The steps for resizing photos in these apps vary depending on the specific software, but generally involve opening the image, accessing the resize or image size tool, entering the desired dimensions, and saving the resized image.
Example: Resizing in Adobe Photoshop
- Open the image: Go to File > Open and select the image you want to resize.
- Access Image Size: Go to Image > Image Size.
- Enter New Dimensions: In the Image Size dialog box, enter the desired width and height.
- Constrain Proportions: Make sure the chain icon between the width and height fields is activated. This maintains the aspect ratio.
- Resample: Choose a resampling method from the dropdown menu. Bicubic Automatic is generally a good choice. For enlarging images, Bicubic Smoother is often preferred. For reducing images, Bicubic Sharper is a good option.
- Resolution: Adjust the resolution as needed.
- Click OK: Click the OK button to resize the image.
- Save the Resized Image: Go to File > Save As to save the resized image with a new name.
Choosing the Right Method
The best method for resizing photos on your Mac depends on your specific needs and skill level:
- Preview: Ideal for quick and simple resizing of single images.
- Photos App: Suitable for basic resizing within your photo library, particularly when you want to adjust relative sizes (Small, Medium, Large).
- Automator: Excellent for batch resizing multiple images with consistent settings.
- Third-Party Apps (Photoshop, GIMP, Affinity Photo): Best for advanced resizing tasks that require precise control over dimensions, resolution, and resampling methods. Also necessary for more complex editing and manipulation.
Tips for Resizing Photos Effectively
Here are some additional tips to help you resize photos effectively:
- Maintain Aspect Ratio: Unless you specifically want to change the aspect ratio, always maintain it when resizing images. This prevents distortion and ensures that the image looks natural. Most resizing tools have an option to constrain proportions or maintain aspect ratio.
- Choose the Right Resolution: Select the appropriate resolution (DPI) for the intended use of the image. For web use, 72 DPI is usually sufficient. For printing, 300 DPI is recommended.
- Experiment with Quality Settings (JPEG): When saving images as JPEGs, experiment with different quality settings to find a balance between file size and image quality. Higher quality settings result in larger file sizes but less noticeable artifacts.
- Use Resampling Methods Wisely: When resizing images, pay attention to the resampling method used. Different resampling methods can produce different results, especially when enlarging or reducing images significantly.
- Avoid Over-Resizing: Avoid enlarging images excessively, as this can result in pixelation and loss of detail. It’s generally better to start with a high-resolution image and reduce its size than to start with a low-resolution image and enlarge it.
- Save a Copy: Always save a copy of the resized image with a different name to avoid overwriting the original image. This ensures that you always have access to the original, high-resolution version.
- Consider File Format: Choose the appropriate file format for the intended use of the image. JPEG is a good choice for photographs and images with gradients. PNG is suitable for images with transparency or graphics with sharp lines and text.
Conclusion
Resizing photos on your Mac is a simple but essential skill. By mastering the techniques outlined in this guide, you can effectively manage your image files, optimize them for different uses, and improve the overall user experience on your website and social media platforms. Whether you’re using Preview, Photos, Automator, or a third-party app, you now have the knowledge and tools to resize photos with confidence and achieve the desired results. Remember to experiment with different settings and methods to find what works best for you and your specific needs.