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How to Resize an Image

One of the most common issues photographers face in the editing process is how to resize an image. So, the Macphun team put together this tutorial to show you the best way to do it! Let’s start at the beginning — the reasons behind why you may want that image resized in the first place.

Reasons for Resizing Images

Today’s cameras and smartphones are more capable of taking pictures at higher resolutions than ever before. This means you get a nice, sharp picture — but it also means the file size can be quite large. This is an advantage when you need to print your photo but it can be a problem for other situations like:

You want to email the photo.

Email hosting companies set limits on the size of files you can attach to an email. Most systems today allow fairly large file attachments, so a JPG file from a digital camera that’s 1-5MB shouldn’t be a problem. Gmail allows attachments of up to 25MB, while 10MB is standard for some other email providers. Still, there may be times when you just want to send a small file for a friend or relative to look at on their own computer, tablet or phone.

You want to upload the photo on the web.

You may occasionally need to upload a picture onto a website for a contest or some other reason. You’ll need to resize the image if the file you want to upload is larger than the maximum file size the website will accept.

Your photo needs to be a specific dimension.

You may run into a situation where you need the image to be a specific dimension. For example, a social media site may require that a photo be no more than 1,500 pixels wide on the longest side or they may specify that it needs to be exactly 1,000 pixels wide.

You want to use the photo on a website or a blog.

It’s important that images on websites and blogs load quickly. The larger the image file, the more slowly it will load. For this reason, images used on websites and blogs should be optimized by making them as small as possible, while still maintaining their image quality. 

Some Common Questions

Here are some common questions you might have about resizing images:

Does Reducing a Photo’s Size Affect Image Quality?

The short answer is that it depends on what we’re talking about. There are two aspects to consider: image quality as it affects printing and as it affects viewing on a monitor or screen.

The number of pixels in an image determines the largest size of the print you can make before the image is no longer sharp. The more pixels, the larger the print you’re able to make.

When you reduce the size of an image, you’re decreasing the number of pixels. This is known as “resampling.” The editing software replaces the configuration of the pixels in the image with a new arrangement. If you reduce the size a great deal, you’ll eventually reach a point where the image will start to degrade. However, since this image would appear very small on your monitor, so you may not notice it.

In general, if you resize a digital image and make it smaller, it will usually appear sharper when viewed on a screen.

Think of it this way: imagine a large picture on your wall that’s slightly out of focus. When you stand close to examine it, you can see it’s blurry. But when you step back far enough, the picture looks smaller and it will appear to be sharper.

What are the Most Common Sizes for Photos?

Standard sizes for photos, in pixels are:

  • 320 x 240
  • 640 x 480
  • 800 x 600
  • 1024 x 768
  • 1280 x 1024
  • How to Resize Photos

    We’ll show you how to resize photos using examples from two image editing programs — Preview for Mac and Luminar by Macphun. It’s not difficult, and once you learn how, you’ll be able to easily and confidently resize a picture whenever the need arises!

    Resizing a Photo in Preview

    1. Open your file in Preview
    2. From the Tools menu, select Adjust Size.
    3. You’ll see the width and height of your image. Make sure there’s a check next to Scale Proportionally and Resample Image.
    4. Change the width to the dimension you need. The height will change automatically to constrain the proportions of your image.
    5. If you’re only intending to display the image on the web or for someone to look at on a computer monitor or a screen, you can set the resolution to 72.
    6. Click OK when you’re done.

    Resizing a Photo in Luminar

    1. From the File menu, select Export to Image.
    2. Select the level of sharpening: none, low, medium, or high.
    3. You have three choices for the method you can use to resize the image:
      • Select Long Edge if you’re only concerned with the size of the longest side. Enter the number of pixels you’d like the long edge to be. It doesn’t matter whether the image is horizontal or vertical. The short side will be automatically be resized to preserve the proportions of the image. This is a good setting to use if you’re resizing a panorama.
      • Select Short Edge if you’re only concerned with the size of the shortest side, ignoring whether the image is horizontal or vertical. Enter the number of pixels for the short edge. The long side will be resized to preserve the image proportions.
      • Select Dimensions to specify the maximum horizontal and vertical measurements. Your image will be automatically resized accordingly. This is helpful if you want horizontal and vertical images to come out the same size.
    4. From here, you can also change the image’s color space, format and quality. Lowering the quality will make the file size smaller but it will also degrade the image. You may not notice the change in image quality if you set the quality level higher than about 50% (halfway).

    After you resize the image, save your new file with a different name from the original file (as you don’t want to overwrite your file).

    When using image editing software, experiment with different features to learn what they can do. From resizing to edits to filters — the possibilities for one single photo are endless.


    From all of us at the Macphun team, expand your knowledge and have fun!

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