Changing the dimensions of a photo is a fundamental skill for anyone working with digital images. Whether you’re preparing images for a website, fitting them into a specific layout, or simply need a different size for sharing, knowing how to resize your photos is essential. Fortunately, macOS provides a straightforward method to adjust image dimensions using its built-in Preview application. This guide will walk you through the simple steps to change the dimensions of your photos on macOS, ensuring they are perfectly sized for your needs.
Using Preview to Resize Your Photos
macOS’s Preview application is more than just an image viewer; it’s a versatile tool that includes basic image editing capabilities, including resizing. Preview allows you to scale your images by percentage, pixels, or even physical measurements like inches or centimeters. You can also adjust the resolution, giving you control over both the size and quality of your image. Let’s explore how to use this tool to effectively change your photo dimensions.
Step-by-Step Guide to Resizing Images in Preview
Before you begin, it’s always a good practice to create a copy of your original image. This ensures that you have a backup and can always revert to the original if needed, as the resizing process in Preview is permanent for the saved file.
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Open your image in Preview: Locate the image file you wish to resize and open it using the Preview application. You can typically do this by right-clicking on the image file, selecting “Open With,” and then choosing “Preview.”
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Access the “Adjust Size” tool: Once your image is open in Preview, navigate to the menu bar at the top of your screen. Click on “Tools” and then select “Adjust Size…” from the dropdown menu. This will open the “Adjust Size” window.
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Choose your unit of measurement: In the “Adjust Size” window, you’ll see options to define the dimensions. You can select your preferred unit of measurement from the dropdown menu. Options usually include pixels, percentage, inches, centimeters, and points. Pixels are commonly used for web and digital display, while inches or centimeters are relevant for print purposes.
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Enter your desired dimensions: Input your desired values for “Width” and “Height” in the respective fields. Consider the purpose of your resized image when deciding on the dimensions. For web use, you might need specific pixel dimensions. For printing, you might work with inches or centimeters.
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Adjust Resolution (if needed): Below the dimensions, you’ll find the “Resolution” setting, measured in DPI (dots per inch) or PPI (pixels per inch). Resolution is crucial for print quality. A standard resolution for web images is typically 72 DPI, while print often requires 300 DPI for sharp details. Be mindful that increasing resolution can decrease image size and vice versa, though Preview primarily focuses on dimension adjustment.
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Confirm and Apply Changes: After entering your desired dimensions and resolution (if you’re adjusting it), click the “OK” button in the “Adjust Size” window to apply the changes to your image.
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Save the Resized Image: To save the resized image, go to the “File” menu and select “Save” or “Save As…” if you want to save it as a new file, leaving the original untouched. Choose your desired file name and location, and click “Save.”
Preview application’s “Adjust Size” window, showing options for changing image dimensions, including width, height, resolution, and unit selection.
Understanding Aspect Ratio and Proportional Scaling
In the “Adjust Size” window, you’ll notice a checkbox labeled “Scale proportionally.” This feature is directly related to the aspect ratio of your image. Aspect ratio refers to the ratio of the width of an image to its height, often expressed as XX:XX (e.g., 16:9 for widescreen).
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Scale Proportionally (Checked): When this box is checked (which is the default setting), Preview will maintain the original aspect ratio of your image as you change the dimensions. This means if you adjust the width, the height will automatically adjust proportionally to prevent distortion. This is usually desired to keep images looking natural and avoid stretching or squashing. However, it might limit your ability to set exact specific width and height if they don’t match the original aspect ratio.
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Scale Proportionally (Unchecked): If you uncheck “Scale proportionally,” you can independently adjust the width and height. While this gives you more freedom to set exact dimensions, it can lead to image distortion if the new dimensions significantly alter the original aspect ratio. Images might appear stretched or compressed. Unchecking this option should be used cautiously, typically when you need to fit an image into a very specific frame and minor distortion is acceptable, or when you are intentionally creating a distorted effect.
To avoid unwanted distortion when resizing, especially if you need to hit precise dimensions that might alter the aspect ratio, consider cropping your image first to the desired aspect ratio before adjusting the size. Cropping allows you to remove parts of the image to achieve a new aspect ratio that better fits your dimensional needs, and then you can resize without distortion using “Scale proportionally” checked.
Choosing the Right Dimensions and Resolution for Your Photos
The best dimensions and resolution for your photos depend on their intended use. Here are some general guidelines:
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Web Images: For websites and online platforms, lower resolutions (72 DPI) and smaller file sizes are preferred for faster loading times. Dimensions should be appropriate for where the image will be displayed – consider the size of image containers on your website or social media platform. Common web image sizes are often in pixels, like 1920×1080 for full-width banners or smaller sizes for thumbnails and in-content images.
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Print Images: For high-quality prints, higher resolutions (300 DPI or more) are necessary to ensure sharpness and detail. Dimensions will depend on the desired print size (e.g., 4×6 inches, 8×10 inches). When preparing for print, it’s crucial to work with pixel dimensions that correspond to the physical print size at the desired DPI.
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Email and Sharing: For sending images via email or sharing on messaging apps, smaller dimensions and file sizes are generally better to avoid large attachments and ensure quick viewing on recipients’ devices.
By understanding how to change image dimensions in macOS Preview and considering the intended use of your photos, you can effectively prepare your images for any purpose, ensuring they look their best while meeting specific size requirements.
