How to Resize an Image in Photoshop
In this tutorial, we’re taking an in-depth look at how to resize an image in Photoshop. This is an area filled with confusion and misinformation which I’m aiming to clear up.
In this tutorial you will learn about:
- Image size and resolution and importantly, which to pay attention to.
- How to resize your image whilst retaining image quality.
- The different Photoshop resizing methods and how to select one.
- Determining the best size for your image.
- A few tips that could improve your image quality.
I’ll be using Photoshop CC (2019) to illustrate the tutorial. If you’re using a different version of Photoshop, you may see some differences in the screenshots to your own computer.
Let’s start by tackling the issue of image size and resolution.
Understanding Image Size and Resolution
When we measure the size of an image, there are all sorts of units we can use. But when it comes to resizing images in this tutorial, we’ll be measuring our images in pixels. An example of this is the image below. This has a dimension of 5,616 pixels wide by 3,744 pixels high.
If you’re wondering what size this is in centimetres or inches, it would depend. That’s because we need another piece of information to determine this, which is the resolution of the image.
The resolution of the image tells us how many pixels there are to each inch (which you can convert to centimetres). Typically, you will see this written as a figure such as 96ppi (pixels per inch) or 300ppi. Once you know the number of pixels and the resolution, you can calculate the size of the image in inches.
To work out how large an image will be, divide the pixel size by the resolution you’re going to use. Let’s look at a quick example:
A photographic print that’s 5,616 pixels at 300ppi. The size is 5,616 / 300 which is 18.72 inches.
Display the same image on a computer screen at 96ppi. The size is 5,616 / 96 which is 58.5 inches.
If we print this image, we can produce a photographic quality print on A3+ paper without needing to resize the image. But if you want to print the image on A2 paper we should enlarge or upscale it.
In contrast, displaying this image on a computer monitor at 96ppi, this image is far larger than we need. It would also need to be resized but to make it smaller, often referred to as downsampling.
Another Image Size to Consider
There is also one other size that we should consider in relation to our image and that’s its storage size. We measure this in kilobytes or megabytes. This is important not just because of the space the image will occupy on a computer but how long it will take to transfer. Consider trying to display a webpage with a 20Kb image and another with a 20Mb image. The page with the 20Mb image will take a lot longer to load and appear a lot slower because there is much more data to transfer. We’ll come back to this point later in the tutorial.
How to Resize an Image in Photoshop
Now you understand the importance of pixels and resolution, let’s look at where we use this in Photoshop. When you want to resize an image in Photoshop you select the “Image” menu and then the “Image Size…” option. Photoshop then displays the “Image Size” dialog which you can see below.
Here we can see the Photoshop Image Size dialog with three numbered areas.
Selecting Image Dimensions (1)
So far, we’ve talked about images having pixel dimensions. Whilst Photoshop supports the entering of pixel dimensions, not everyone wants to work with pixels. Some people may want to work in units such as inches, centimetres or even %. If you look to the right of the word “Dimensions” in the dialog you will see a small drop-down arrow. Click this and you can switch to any of the other units supported by Photoshop as shown below. For this tutorial, we’re going to continue to work with Pixels.
You’ll also see another drop-down list in this section which is “Fit To”. This contains a list of commonly used sizes which you can select as well as define new presets to appear in the list. If you regularly need to work with a specific set of dimensions, this can be a real time saver.
Setting the Size and Resolution (2)
In this section of the Photoshop dialog, you can set the size and resolution of the image to resize it. Here you can enter the new Width and Height of 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.
There’s another feature in this section of the dialog that you need to be aware of which is the Aspect Ratio lock. This is a small icon to the left of the words Width and Height. When this lock is on, Photoshop will lock 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. This maintains the aspect ratio of the image. You can see the icon indicated in the screenshot below.
If you click this link icon to turn it off, you can enter any new Width and Height measurements without Photoshop trying to calculate the other. But do remember, if these new values aren’t in the same proportion as the original Width and Height of the image, it will distort the image.
Resampling Options (3)
In the third section of the dialog are two important options for resizing your image in Photoshop. The first is the Resample tick box. When there’s a tick in this box to select it and you resize an image, Photoshop will create or remove pixels. A quick example should help explain this.
Earlier, we talked about resizing the image to 9,000 x 6,000 pixels at 300ppi to create an image that was 30 x 20 inches. When we entered the new image dimensions, the Resample option instructed Photoshop to create new pixels. This is how we maintained the 300ppi resolution. If we didn’t have the Resample option ticked, Photoshop wouldn’t create any new pixels. In fact, you wouldn’t even be able to enter a new pixel dimension because that option’s disabled. You can, however, switch to entering the new image size in inches. Entering a new image size of 30 x 20 inches would see the Resolution drop from 300ppi to 187.2ppi. Importantly, the image would still be 6,000 x 4,000 pixels because no new pixels have been created.
If you want to change the pixel dimension of an image you must use the Resampled option.
When you’re resizing an image using the Resample option, you should also be aware of the interpolation options. These are in the drop down to the right of the Resampled option. You can see them in the screenshot below.
Photoshop uses these interpolation options or routines to create or remove pixels from an image. Each option has its strengths and weaknesses which means you should find the best match to the image you’re trying to resize.
Photoshop has seven different interpolation routines it can use but there is also an eighth option in the list which is “Automatic”. As mentioned, each of the routines has its strengths and weaknesses and Adobe has indicated this “best purpose” in the list. For example, “Nearest Neighbor (hard edges)” is good for resizing graphics with hard edges but not photographs.
The Automatic option is possibly the easiest to use. When selected, Photoshop will choose which interpolation routine to use based on what it thinks you are trying to do. This usually produces good results but, it might not always produce the best result. Personally, I’ve never experienced a problem resizing simple graphics (I don’t do this often though), but I have sometimes achieved better results when resizing photographs.
If you’re resizing a photograph, it’s worth taking the time to check the different interpolation options. This is particularly true if the resizing will be greater than 200% or less than 50%. For example, when scaling an image to 200% or more, Photoshop’s “Automatic” option will use the “Preserve Details (enlargement)” routine. Sometimes this will produce an image that’s too sharp and has exaggerated detail. When this happens, you may be able to achieve a more natural result by selecting the “Preserve Details 2.0” option.
A similar problem can occur when downsampling an image to less than 50% of its original size. Photoshop will probably use the “Bicubic Sharper (reduction)” routine which can cause the image to appear unnaturally sharp. If you see this problem, try switching to “Bicubic Smoother (enlargement)”. You can then apply any additional sharpening after the image has been resized.
The Stair-Step Myth
At this point, I should mention the stair-step routine, although you won’t see this listed. I’m calling this a myth because whilst it was once true, I’m not sure it is today.
Back in the earlier days of Photoshop, there were only a couple of options for resizing an image. Whilst these were quick, none of them was particularly effective when making significant photographic enlargements. And because digital cameras typically had a much lower resolution then, making photographic enlargements was a common activity.
This is when someone realized that by enlarging an image in Photoshop by just 10%, the results were very good. Importantly, if you repeated the enlargement of the resized image by 10%, the results were still very good. And you could repeat this process multiple times to achieve high-quality enlargements. Whilst this method still produces good results today, I’ve not seen it improve on the latest Photoshop routines, but you can try it if you like.
What Size Image Do You Need?
We’ve now covered a lot of ground and you should have a good idea about resizing an image in Photoshop. The question then comes, what size image do you need. Let’s look at this in two parts; first, increase the size of an image and then reducing the size.
Increasing Image Size
I’m going to assume that most of the time when you’re resizing an image, it will be a photograph. Also, that you want to resize the photo so that you can make a print, possibly a very large print. After all, most today’s digital cameras produce images which already have a large pixel dimension already.
The most important step in resizing is to determine what resolution you need the resized image to be. Most photographers will assume 300ppi is the best resolution to use but that’s not always true. The best resolution when printing is determined by something called the native resolution of the printer. For consumer or prosumer printers, Epson printers have a 360ppi native resolution whilst most other manufacturers use 300ppi. If you’re printing with a professional series printer or using a print bureau, check the best resolution to use.
The native resolution of the printer is determined by the number of nozzles in the print head measured over an inch. If your image doesn’t have the same resolution as the printer, it will be resized by the printer to its native resolution. This is often less effective than correctly resizing the image prior to sending it to the printer. In fact, some printing software such as Lightroom and Qimage will automatically do this resizing for you, based on the printer you’re using.
The advice then when resizing an image for print is to first determine the native resolution of your printer. Then, based on this resolution, enter the new image size in Photoshop at that resolution. You can then select the best interpolation routine to use by judging the results in the preview window.
Reducing Image Size
If you’re reducing the size of an image to produce a print, it’s probably best to follow the advice above. There’s little benefit in printing a large print small by allowing the image resolution to increase. But, the main reason for reducing an image size probably won’t be for printing. It’s more likely to be for displaying images on web pages. This then introduces the important consideration of image size for storage and data transfer.
If your resized image is for a web page, the image needs to be as small as possible. This means it can quickly transfer to the viewer’s browser and the web page will load very quickly. At the same time, you will want the image to appear at the best possible quality, so it becomes a balancing act.
If you’re using a photo sharing service (for example Flickr or SmugMug) to show your photography, it will automatically optimise your image. This means the image will be resized and compressed so that the storage is minimised and the page speed is maximised. You won’t have any control over this, but don’t worry as most people can’t see any difference between the original and optimised versions.
If though you’re resizing an image because you’re building your own website, you will need to do the optimisation yourself. This is something I do a lot so let me share with you a few key points to help:
- Forget about the resolution of the image as there are too many variations these days. Whilst 96ppi was the resolution for Windows and 72ppi a Mac, this is no longer the case. Despite this, you will need to enter a resolution into Photoshop when resizing your image, so just use 96ppi.
- Focus instead on creating the correct image dimensions as measured in pixels. For example, my website has a page width of 1,080 pixels so that’s the widest image I need. There’s no point creating an image that’s 2,000 pixels wide as the web browser won’t show those additional pixels. 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 means saving it as a JPEG (or PNG if the image is a graphic) with a reasonable compression ratio. I tend to use a JPEG quality setting of 6 but sometimes a 7 or 8 if I can see compression problems in the image.
Sharpen Your Resized Image
Something that we haven’t yet touched on is sharpening your images. This is an important step as resizing an image can reduce or exaggerate sharpening. The best approach is to resize your image first following the advice in this tutorial. You can then optimally sharpen the resized image. Of course, if there is subsequent image compression this can affect the sharpness of the image. I do though find that the compression works well with images that have been correctly sharpened.
We’ve now finished our review of the various points to consider when resizing an image using Photoshop. If you want to achieve the best quality results the following are the key points to remember.
- Understand the best resolution and dimensions for your image before resizing it.
- Select the best interpolation method in Photoshop depending on the image content and if it’s being upscaled or downsampled.
- Sharpen your image after resizing and where possible after compression.
When you follow this advice, you should be able to achieve excellent image resizing with Photoshop.
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