These days even budget digital cameras have 14- or even 16Mp sensors. That says practically nothing about the quality of the resulting photos, but it does mean they tend to take up a lot of space on your memory card, and on your computer's hard drive.
Attempting to share these photos with friends and family via email is awkward since even a couple of pictures is likely to hit the maximum size limit for attachments. You could go down the Facebook route, but not everyone has (or wants) a Facebook account. Plus, if friends or family want to print the photos, the low-resolution versions of your shots won't look great at large sizes.
It's therefore important to understand how to resize digital photos so they're the appropriate resolution for printing, emailing, posting on the web and more.
A digital image has two basic attributes: file size and resolution. The two aren't directly linked, so a large file size won't necessarily indicate a high resolution. An image's resolution in megapixels is the number of horizontal pixels multiplied by the number of vertical pixels (a pixel is essentially a dot made up of one colour).
A 16Mp camera will produce photos with a typical resolution of 4600x3400. That's way too much detail for a typical laptop, which will have a screen with 1366x768 pixels. Even a full HD TV or PC monitor has only 1920x1080 pixels.
What this means is that the photo has to be scaled down to fit on these screens, and you don't see all the detail unless you zoom in.
For most people, the extra detail isn't noticeable so you could shrink (resize) your photos to one of these lower resolutions to make the files smaller and enable you to email more in one go, or make it a lot quicker to upload them to a photo-sharing website or social network. You can also increase the amount of compression if you want to make really small files, although this can lead to smudgy and smeary photos if you go overboard.
Many websites will automatically downsize your pictures when you hit the Upload button, but this gives you no control over how much compression is used, and what resolution they become. Here, we'll show you how to resize photos in Photoshop (the same steps work in just about every version of Photoshop - we're using CS5) for complete control.
You might also like to know about the free ImageResizer utility which lets you resize photos by right-clicking on them in Windows Explorer. You can download it from imageresizer.codeplex.com
How to resize photos in Photoshop
Step 1. Open the image you want to resize. Click the Image menu and then Image Size… to bring up the properties window. Ensure the Constrain Proportions box is ticked and enter a new value in the Width box. You'll see the Height box filled out automatically. Notice that the Document size also changes, indicating the size the image will print at the selected resolution.
2. At the bottom is a drop-down menu where you can change the algorithm used when resizing the image. It's hard to tell the difference between them, but Bicubic Sharper is the recommended option when making your images smaller. When you've finished making changes, click Ok to apply them.
3. If you want your image to match the resolution of your monitor in order to use it as wallpaper you will need to crop the image as photos don't have the same aspect ratio as PC displays. Assuming you have a 1920x1080 monitor, select the Crop tool (press C) and enter 1920 px and 1080 px in the Width and Height boxes. Click and drag to select the area of the photo to keep, then double-click to crop to those dimensions.
4. If you're resizing images for the web, try to use the pixel dimensions that the image will actually appear on the web page. This is usually less than 1000 pixels wide, and may even be less than 500 pixels. A Facebook banner image, for example, should be 851x315 pixels, and the equivalent for Google+ is 940x180 pixels.
5. When saving the resized photos, you'll be given the choice of a variety of formats and compression levels. First, make sure you choose Save as… rather than save, as you should preserve a copy of the original, full size image. After choosing a format (usually JPG) and entering a filename, click Save and then adjust the quality slider to trade off file size against image quality.
6. If you plan to print the image, you should resize the image using the Document Size settings mentioned in Step 1. You shouldn't need more than 300 pixels per inch, and may get away will as little as 200. Uncheck the Resample Image box first, then make your changes to avoid scaling up the image.
Next page: resize multiple photos - batch resizing