How to Resize an Image on Mac Without Losing Quality (2023 Guide)

As a Mac user, resizing images is a common task you‘ll likely encounter, whether for sharing photos online, sending via email, using in documents, uploading to a website, or printing. However, you may be worried that resizing an image will reduce its quality.

The good news is, if done properly, you can resize images on your Mac without a noticeable loss in resolution or clarity. As someone who regularly resizes images for my graphic design work, I‘m excited to share with you the best methods and practices to achieve great results.

In this comprehensive guide, I‘ll walk you through multiple ways to resize an image on Mac, including step-by-step instructions for:

• Using Preview (built-in Mac app)
• Using the Photos app
• Using online resizing tools
• Creating an Automator quick action
• Using third-party image editors

I‘ll also dive into factors that impact the quality of resized images and share tips for maintaining resolution when scaling images up or down. Whether you‘re a beginner or a pro, by the end of this article you‘ll be able to confidently resize your images for any project or purpose. Let‘s get started!

Why You May Need to Resize an Image on Mac

There are several reasons why you might want to resize an image on your Mac:

1. Reducing File Size
Full resolution photos, especially those taken with newer smartphones or digital cameras, can have very large file sizes. Resizing allows you to shrink the dimensions and file size to make the image more suitable for:

• Attaching to an email
• Uploading to a website or social media
• Saving storage space on your Mac or iCloud

2. Fitting Images into Documents or Layouts
When creating content like presentations, documents, flyers, etc. you‘ll often need to adjust image sizes to fit the layout. Resizing allows you to scale images up or down to match the available space.

3. Optimizing for Web or Print
The optimal image size is different for displaying on screens compared to printing. For the web, you generally want smaller file sizes to ensure fast page load times. For print, you need sufficiently high resolution for sharp details. Resizing helps you create versions of an image tailored for each medium.

4. Standardizing Image Sizes
When dealing with a collection of images, you may want them to have matching dimensions for consistency, such as making all product photos the same size for an online store. Batch resizing is useful in these cases.

Now that we know some common scenarios for resizing images, let‘s look at how to actually do it on Mac.

Using Preview to Resize Images on Mac

Preview is the default app for opening images on Mac, and it has built-in tools for basic editing like resizing. Here‘s how to use it:

Step 1: Open the image you want to resize in Preview. You can do this by double-clicking the image file, or right-clicking it and selecting Open With > Preview.

Step 2: Click the Edit button (looks like a pencil) in the Preview toolbar.

Step 3: Click the Adjust Size button. This opens a window with options to change the image dimensions and resolution.

Step 4: In the "Adjust Size" window, you can specify new values for width/height in pixels, inches, cm, mm, or percent. As you change a value, the others will automatically adjust to maintain the aspect ratio (proportional resizing).

To resize by an exact percentage, choose "percent" from the drop-down, uncheck "Scale proportionally" and enter a percentage value to scale the width and height equally.

Step 5: Click OK to apply the changes. Then go to File > Save to overwrite the original image with the resized version, or File > Export to save a copy at the new size.

Pro Tip: If you‘re enlarging a small image or shrinking a very large one, check the "Resample image" box. This tells Preview to optimize the pixels for the significant change in size. But avoid checking it for minor size changes, as resampling can slight softness to the image.

Using the Photos App to Resize on Mac

The Photos app, where your iPhone photos and digital camera imports live, also lets you easily resize images.

Step 1: Open the Photos app and find the image you want to resize.

Step 2: Double click the image to view it full screen.

Step 3: Click the Adjust button (looks like a dial) to reveal editing options.

Step 4: Click the Crop button. This will bring up handles on the corners of the image.

Step 5: Click and drag any handle to resize the image proportionally, or click and drag a corner handle while holding the Option key to resize non-proportionally. You can see the pixel dimensions update in real time in the toolbar.

Step 6: If you want a specific aspect ratio or size, click the Aspect Ratio button in the toolbar. You can choose common ratios like Square, 4×3, 16:9 or enter a Custom ratio or size in pixels.

Step 7: When finished resizing, click Done. Your changes will be saved as part of the image‘s edit history in Photos.

To export a copy of the resized image outside the Photos library:

1. Select the image
2. Go to File > Export > Export X Photos…
3. In the export dialog, choose your desired file type (JPEG, PNG, TIFF) and select a size from the list (small, medium, large, full size). Click Export.

Online Tools for Resizing Images

There are many free web-based tools that let you quickly resize an image without needing an app. These can be handy for one-off resizing when you don‘t want to bother opening an app. A few good ones:

• Online Image Resizer – Simple interface for resizing by pixels or percentage, has options to crop and compress file size.

• PicResize – Can resize using pixel dimensions, percentages, or X/Y ratios. Supports JPG, PNG, GIF, TIFF, BMP files.

• Rsizr – Clean, easy to use resizing plus has advanced options like DPI, sharpening, filters. Lets you resize multiple images at once.

To use an online resizing tool:

1. Go to the website
2. Click button to upload your image (or paste an image URL)
3. Enter your desired dimensions or choose a preset
4. Click a button to execute the resize and see a preview
5. Download the resized version of your image

While online tools are convenient, I recommend using a desktop app for frequent resizing jobs or sensitive images, since uploading exposes your data to the web service.

Batch Resizing Multiple Images on Mac

Have a folder full of images you need to resize to the same dimensions? Instead of doing them one-by-one, you can automate the process to resize images in bulk on Mac.

There are a couple ways to set up batch resizing:

1. Using Preview

• Select multiple images in Finder
• Right click and choose Open With > Preview
• In Preview go to Edit > Select All
• Go to Tools > Adjust Size
• Enter your target size/resolution, click OK
• Go to File > Export Selected Images… to save the resized files

2. Using Automator

• Open Automator and choose "New Document"
• Select "Quick Action" and click "Choose"
• Set the workflow to receive "Image Files" in "Finder"
• Drag the "Scale Images" action into the workflow
• Set your desired image size in pixels
• Click File > Save and give your Quick Action a name like "Resize to 1200px wide"

Now you‘ll be able to right-click on one or more images in Finder and use your Quick Action in the Services menu to instantly resize them to your preset dimensions. Super handy!

Tips for Resizing Images to Maintain Quality

To avoid ending up with pixelated or blurry images after resizing, follow these tips:

1. Start with high quality images
The better the source image, the better the resized result. Avoid using small, low-resolution files as your starting point when you need to enlarge. Web images are often too low res for print. When possible, use the original, full size version straight from your camera or phone for resizing.

2. Keep the same aspect ratio
Maintain the original proportions of the image to prevent stretching or squishing. Use the "scale proportionally" option in Preview or lock the aspect ratio when resizing in other apps. If you must change the aspect ratio, crop the image to the desired proportions first, then resize.

3. Aim to reduce resolution, not increase it
In general, you‘ll get better results scaling an image DOWN in size than scaling UP. Enlarging images, especially by a lot, can introduce pixelation because the software has to "invent" new pixel data that wasn‘t in the original image. If you MUST enlarge, use an app with advanced upscaling algorithms like Gigapixel AI.

4. Use the right resizing method
For significant enlargements (2X+), choose the Preserve Details (enlargement) option in Preview, or a dedicated app for enlarging. For extreme shrinking, pick the Reduce Noise option to avoid artifacts. Between 100-50%, use the default Bicubic algorithm.

5. Choose the best file type
For photos, use JPEG at a quality level of 80-90 (high enough to maintain detail but not so high the file size is huge). For graphics with large areas of solid color, use PNG. Avoid resaving JPEGs multiple times, as the lossy compression adds up.

6. Sharpen after resizing
Resizing can slightly soften details, so add a gentle sharpen to make edges crisp again. In Preview, go to Tools > Adjust Color and move the Sharpness slider slightly right. Don‘t oversharpen or you‘ll get halos and artifacts.

Common Resizing Purposes & Optimal Sizes

Here are suggested image sizes for different uses:

• Email attachment: 500-1000 pixels wide
• Social media post: 1080-2000 pixels wide
• Website hero image: 1500-2500 pixels wide
• Website thumbnail: 200-500 pixels wide
• 4" x 6" print: 1200 x 1800 pixels
• 8" x 10" print: 2400 x 3000 pixels
• Poster print 24" x 36": 7200 x 10800 pixels

Start with these as a general guide, but refer to the specific requirements of the website or printer you‘re using for the most accurate specs.

FAQs About Resizing on Mac

Q: What‘s the difference between resizing and cropping?
A: Resizing changes the dimensions and number of pixels in the entire image. Cropping cuts away outer portions to create a smaller area while preserving the original resolution.

Q: Is resolution the same as file size?
A: No, resolution refers to the number of pixels in the dimensions (e.g. 1200 x 1800), while file size is the number of bytes the image data takes up on disk (e.g. 2.5 MB). But in general, higher resolution = bigger file sizes.

Q: How can I check the current size and resolution of an image?
A: Select the image in Finder and press Command+I to open the Info window. Under More Info you‘ll see the pixel dimensions and file size. Or open the image in Preview, click Tools > Show Inspector and go to the General Info tab.

Q: What resolution do I need for printing photos?
A: For prints, aim for 300 pixels per inch at the intended print size. So a 4×6" print at 300 PPI would be 1200 x 1800 pixels. But check with your print service, as some recommend specific resolutions for best results on their equipment.

Alternatives to Preview for Image Resizing

While Preview is great for basic resizing, you may need more control or options for certain tasks. Here are some other Mac apps to consider:

1. Pixelmator ($40)
Pixelmator is a full-featured image editor with advanced resizing controls like content-aware scaling, custom resizing presets, and preserving metadata. Great for pros or frequent image editors.

2. PhotoBulk ($10)
If you primarily need to resize images in bulk, PhotoBulk is an affordable option. It has a simple drag-and-drop interface for batch processing and can handle large quantities of images quickly.

3. Acorn ($40)
Another powerful image editor, Acorn offers non-destructive resizing, meaning you can always undo or change the dimensions later without quality loss. Also has advanced features like resizing via a percentage or custom formula.

While Preview can handle most everyday resizing needs, these apps are worth the investment if you frequently work with images or need pixel-level precision.

Conclusion

We covered a lot of ground! You now know multiple ways to resize an image on Mac, how to maintain quality when scaling, optimal sizes for common uses, and more. As you can see, Preview is a capable tool for most basic resizing jobs. But there are plenty of alternatives if you need more advanced control.

The key takeaways:

• Use the highest quality source image possible
• Keep the original aspect ratio to avoid distortion
• Scale down in size instead of up when you can
• Sharpen after resizing for best detail
• Choose the right file type and dimensions for your needs

I hope you found this guide helpful! With practice, you‘ll be able to expertly resize images for your projects while preserving resolution and detail. Happy resizing!