How to Resize an Image in Photoshop
How to Resize an Image in Photoshop the Ultimate Guide
This tutorial explains how to resize an image in Photoshop. You will learn about:
- The link between image size and resolution and which to pay attention to.
- How to resize an image in Photoshop whilst retaining image quality.
- The different Photoshop resizing methods and which to use when.
- Determine the best size for your image.
- Tips to improve quality when resizing an image.
I’ll be using Photoshop CC to illustrate how to resize an image, but most of the information applies to earlier versions as well.
Let’s start by addressing the difference between image size and resolution. This is important when resizing an image in Photoshop.
Understanding Image Size and Resolution
We can express the size of an image using different units of measurement. In this tutorial, we’ll be measuring our images in pixels because it applies to most situations. For example, this next image has a dimension of 5,616 pixels wide by 3,744 pixels high.
But if we wanted to state it’s size in centimetres or inches, we need another piece of information first. The resolution.
The resolution of the image tells us how many pixels there are to each inch or centimetre. Usually this is written as a figure like 96ppi or 300ppi. The “ppi” after the number stands for Pixels Per Inch. This is the number of pixels in an inch if we were to print the image. When you know the number of pixels and the resolution, you can calculate the size of the image in inches. You just need to divide the dimensions of the image by the resolution:
If an image is 5,616 pixels wide with a resolution of 300ppi, it would produce a print 18.72 inches wide; that’s 5,616 pixels divided by 300.
Whilst this is useful information if you are going to print an image, most of the time you don’t need it. That’s because most images now only appear on computer screens and the internet. When that happens, the resolution is ignores in most cases. What’s important are the pixel dimensions (height and width) of the image. If the image is too big or too small, it’s going to cause problems.
How to Resize an Image in Photoshop
Now you understand the importance of pixels and resolution, let’s look at where we use this when resizing an image in Photoshop.
Start by opening the image you want to resize in Photoshop. Then click the Photoshop “Image” menu and the “Image Size…” submenu option.
Photoshop then displays the “Image Size” dialog which you can see below.
The three numbered areas in the illustration are important controls for resizing the image:
- Unit of measurement for the resizing.
- Size and resolution of the resized image.
- Resampling method used for increasing or reducing the image size.
Let’s look at these in more detail and see how best to use them.
Selecting Image Dimensions (1)
So far, we’ve talked about images using pixel dimensions, but you can use other units of measurement for the resizing. For example, if you are producing a physical print from the image you may want to resize the image using inches or centimetres. This is where you can change the Image Size dialog to use different units of measurement.
Look to the right of the word “Dimensions” in the dialog where you will see a small drop-down arrow. Click this to display a dropdown with the different units supported by Photoshop. Select the option you want to use.
Below this list is another dropdown titled “Fit To”. This contains a list of commonly used sizes which you can select. These presets can help save time if you regularly need to use one of these sizes. When you select one of thee presets, you will see the dimensions in the Width and Height boxes change.
The default when opening the Image is “Original Size”. We will use this for our example so we can manually set the Width and Height for the resized image.
Setting the Size and Resolution (2)
This is where you can enter the Width and Height for Photoshop to use when resizing the image. For example, if we wanted to create a print of our image which was 30 inches (at 300ppi), we would 9,000 pixels (30 x 300) for the Width. We would also enter 300 Pixels/Inch in the Resolution box.
Another example is if we want to create an image for a YouTube thumbnail that’s 1920 x 1080 pixels. We would enter those dimensions in the Height and Width and ignore the Resolution setting.
Aspect Ratio Lock When Resizing an Image
But there’s another feature in this section of the dialog that you need to be aware of, the Aspect Ratio Lock. If you’ve just tried entering 1920 x 1080 pixels to resize an image, you may have come across a problem. After entering Width, you will see the Height change automatically. That’s because the ratio between the width and the height measurements is fixed or locked by the Aspect Ratio Lock
This is the small chain icon to the left of the words Width and Height. When this lock is on, Photoshop locks the aspect ratio of the image. This means if we entered a new image width of 9,000 pixels, Photoshop automatically calculate the new Height to be 6,000 pixels.
Locking the aspect ratio of the image ensures the image isn’t distorted when resizing.
When you click the link icon to toggle it off, you can enter any new Width and Height measurements without Photoshop recalculating the other. The drawback is that it will distort the image when it’s resized.
If you need to use a set pixel width and height for a social media post for example, you probably don’t want to distort the image. That’s when you will need to use the Photoshop Crop Tool rather than resizing the image.
Resampling Options (3)
The third section of the dialog has two important options for resizing your image in Photoshop. The first is the Resample tick box. When there’s a tick in this box and you resize an image, Photoshop will create or remove pixels by resampling the image.
Earlier, we talked about resizing the image to 9,000 x 6,000 pixels at 300ppi to create a 30” x 20” image. When we entered the new image dimensions using the Resample option, we tell Photoshop to create new pixels in the resized image. This is how we maintained the 300ppi resolution.
If we don’t use the Resample option, Photoshop doesn’t create new pixels. Instead, it changes the resolution of the image to change its size. For example, resizing the image to 30” x 20” causes the Resolution to drop from 300ppi to 187.2ppi.
Remember, if you want to change the pixel dimension of an image when resizing, you must use the Resampled option.
The other option in this area of the dialog is the resampling method. When you use the Resample option you can also choose the method in the dropdown as shown below.
These resampling methods are called interpolation options or routines. These are how Photoshop calculates where and how to produce the new pixels to resize the image. Each of these has different strengths and weaknesses depending on the image you’re trying to resize. Let’s have a look at a few.
Photoshop Interpolation Routines
Photoshop has seven different interpolation routines it can use as well as an “Automatic” option. Because each routine has its strengths and weaknesses, Photoshop indicates the possible “best use” next to it in brackets. For example, “Nearest Neighbor (hard edges)” is good for resizing graphics because they tend to have hard edges. But it’s not very good for photographs as they have many more edges that usually aren’t well defined.
The “Automatic” option tries to automatically select the best interpolation routine based on what Photoshop determines is the content of the image. This usually produces good results but, it might not always produce the best result.
If you’re resizing a photograph and quality is important, it’s worth checking the different interpolation options. For example, when resizing a photograph to 200% or more, Photoshop’s “Automatic” option will probably use the “Preserve Details (enlargement)” routine. Sometimes this will produce an image that’s too sharp, with exaggerated detail. If this happens, you may achieve a more natural result by selecting the “Preserve Details 2.0” option.
A similar problem can occur when down sampling an image to less than 50% of its original size. Photoshop will probably use the “Bicubic Sharper (reduction)” routine which can cause images to appear unnaturally sharp. If you see this problem, try “Bicubic Smoother (enlargement)”. You can always apply additional sharpening after the image has been resized.
The Stair Step Method
At this point it’s worth mention the stair step routine, which isn’t listed.
Back in the earlier days, Photoshop only had a couple of options for resizing an image. Whilst these were quick, none of them were particularly effective for significant photographic enlargements.
This is when someone realized that when enlarging an image by only 10%, Photoshop produced good results. Then, if you repeated this to resize the image by another 10%, the results were also good. Then it was possible to resize the image by another 10% and then another, and so on. Using this method, it was possible to produce significant image enlargements whilst retaining the image quality.
Whilst this method still produces good results today, the latest Photoshop routines are probably better and certainly easier.
What Size Image Do You Need?
Now that you understand how to resize an image in Photoshop, let’s look at the question of what size image you need and are you increasing or reducing the image size.
Increasing Image Size
Most of the time when increasing the size of an image, it will be a photograph. It’s also likely that you will be doing this to make a print, possibly a very large print.
The most important step in resizing is to determine what resolution you need the resized image to be. Most photographers assume 300ppi is the best resolution for printing but that’s not always true. The best resolution when printing is determined by something called the native resolution of the printer. Epson printers usually have a 360ppi native resolution whilst most other manufacturers use 300ppi. But if you’re printing with a professional print service, check the best resolution to use. It’s often different to these.
The advice then when increasing an image for print is to first determine the resolution of the image. Then, using this you can enter the Width, Height and Resolution settings in the Image Size dialog.
After entering the dimensions and resolution of the resized image, select the best interpolation routine. If you don’t want to test the different options, use the “Automatic” setting.
Reducing Image Size
When reducing the size off an image for print, it’s probably best to follow the advice above. There’s little benefit in printing a large image small by increasing the resolution.
But the main reason for reducing an image size is probably for displaying the image on the internet. This introduces the important consideration of image size for storage and data transfer.
When you resize an image for the internet, the image needs to be small. This means don’t make the dimensions unnecessarily large and ensure its size on the disk is small. It can then quickly transfer to the viewers browser allowing the web page to quickly load. At the same time, the image needs to appear at the best possible quality, so it becomes a balancing act.
If you’re using a photo sharing service, the images you upload are usually optimised for you automatically. But if you’re resizing an image for your own website, you will need to optimise it yourself.
Here are a few key points to help:
- Forget about the resolution. Whilst 96ppi was the resolution for Windows and 72ppi a Mac, this is no longer the case. There’s no need to bother changing the resolution setting in Photoshop.
- Focus instead on creating the correct image dimensions as measured in pixels. If the website has a page width of 1,080 pixels there’s no point creating an image that’s 2,000 pixels wide. All that happens is the image takes longer to download, slowing the display of the page.
- Save your resized photo in a format optimised for the web. This usually means saving it as a JPEG (or PNG if the image is a graphic) with a reasonable compression ratio. A JPEG quality setting of 6 is usually a good starting point.
You should now understand how to resize an image using Photoshop as well as some important points to consider around quality.
If you want to achieve the best quality results the following are the key points to remember.
- Understand the best resolution (if it’s needed) before resizing your image.
- Select the best interpolation method in Photoshop depending on how and what you are resizing your image for.
- Consider sharpening your image after resizing.
Follow this advice and you should be able to achieve good image quality when resizing an image with Photoshop. But if you want to achieve excellent image quality, consider using a dedicated resizing tool like Topaz Gigapixel.
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