As the megapixel size of cameras get larger (the standard size seems to be 8 megapixels and larger), it means that the photos from your camera will be larger in pixel and document dimension sizes. These larger sizes do matter when it comes to printing, emailing, or posting images on a website. Any version of Photoshop can resize images and prepare them for various output purposes.
Before we get into basic methods about how to resize images, let me remind those of you who are new digital photography that an 8, 12, or 15 megapixel camera does not mean that it will make better photos or that it’s a professional camera. The megapixel size of a camera impacts the maximum size of the prints that can be made.
So for example, a 12MP (4000 x 3000 megapixels) camera can print upwards to a 16″ x 20″ image at 240dpi, but that doesn’t mean it will be excellent photo quality. Check out Tiporama which includes an Image Size Calculator to convert pixel and resolution sizes into physical image width and height in inches. This digital camera photography chart is also another good resource understanding pixel sizes and corresponding print sizes.
So now let’s look at how to resize images in Photoshop. To follow along with this tutorial, you might want to launch an original photo in Photoshop that you have recently made with your camera.
First, to get the size information about an image in Photoshop, click on Image>Image Size in the menu bar. The resulting dialog window will tell you all the information you need to know.
- At the top, you will get Pixel Dimensions and actual file size of the image. The image file used in this tutorial came from a Canon Powershot G9, a 12MP camera. The photo was shot in the highest JPG quality mode. If it had been shot in RAW format, the file resolution size would have been even larger. Notice in the screenshot above, if you increase the resolution size of the image, it will in turn increase the file size. So if you’re wondering why your computer or external drive is filling up so fast, it could be attributed to the number and file sizes of the photos or song files you’re importing into your memory drive. Photos taken with larger megapixel size cameras will eat up space on your hard drive very fast. That’s why you need a large external drive to house image files. And it’s also why you don’t want to hang onto image files that you’re not going to use or were poorly shot.
- In the same box, you also get the actual pixel width and height of the image. So if you know a particular pixel size that you need for say website posting, you can make those changes here. For example, you might need to change the pixel size to 800 x 600 or smaller. If you want the image to fit and display in an email, you will make it even smaller in pixel size.
- This dialog box also provides actual physical document size of the image. In this example, we see that the photo is about 22 x 16 inches. Resolution essentially refers to image quality of the photo. Typically, if you’re resizing an image to post on a website, the resolution size should be between 72 and150 dpi. If you’re printing the image, it should between 240 and 300dpi. For most normal size prints, 240dpi is sufficient. Changing the resolution will not change the physical dimensions of the size. It will only change the pixel quality of the image.
- The last important part of this box has to do with constraining the proportions and re-sampling the pixels of a selected image. When you change say the width of the photo, Photoshop will automatically adjust the appropriate image height. If the Constrain Proportions is not checked, the dimensions of your image might become skewed.
Resizing the Image
To resize images in Photoshop, you first want to make a duplicate of the original photo so that you can always re-use its original size if need be. You can do this quickly by selecting Image>Duplicate in the menu bar. If you don’t duplicate, you can select File>Save As (not Save) to save a copy of the resized image.
With the Image Size box opened, you can change either the pixel size or document size of the image by simply changing the numbers to the size you need. Be sure to keep the Resample Image and Constrain Proportion boxes checked.
However, notice that if you need a specific dimension size, such as 8″ x 10″, using the original dimensions might not work proportionally for printing. Since most consumer cameras are not full frame, you might lose some portions of your image when it is printed. Sometimes you notice that when you get images printed, a part of the image might get chopped off. In the screenshot above, you’ll notice that if I want to change the document size to 10″ x 8″, Photoshop changes the size to 10″ x 7.5″ in order to keep the width and height proportional. If the image is printed full bleed at 10″ x 7.5″ on 8″ x 10″ paper, one side of the image will have .5 inches of white space on it. That wouldn’t look very good.
Crop for Size
So the best way to resize images for printing is to crop it to the size you need. To do this, simply close out of the Image Size box without clicking OK, and then select the Crop tool in Photoshop. Below the menu bar of Photoshop, you will see the width and height fields where you can type in the exact dimensions you want. Be sure to put “inches” or “in” after each number. You can also add the resolution size.
Now just click on the image, hold down the mouse button and drag your cursor to the maximum width and height of the crop you set. After your release the button, you can see what part of the image needs to be cropped in order to get the size you want. You can click on the image again and move the crop to change which side/part of the image you want to crop out. After your crop is set, click the Return key and Photoshop will make the crop.
Resize Images for the Web
You no doubt know that it’s nearly impossible to post or email large image files, such as a 32MB or 2400 x 1800 pixel image. It needs to be resized so that it can downloaded off the web page faster or emailed and opened easily by the recipient. In order to do this, you will want to open the Image Size box as described above, and change the resolution to 72 or 150dpi. Also change the pixel dimensions of the image to the size you want, say 800 x 600 pixels.
Next, click File>Save for the Web, and a dialog box will open. There are three basic parts of this box that you will want to be familiar with.
- At the bottom left, you will see the current pixel size of the image. You will also see the approximate amount of time it might take for the image to download, on say a slow server. Typically you want the pixel size for web posting to be under 120KB so the image will load pretty fast on a web page.
- If you need to change the pixel size of the image, you can click on the Image Size panel and change the numbers there. Experiment with changing the numbers and notice how it changes the pixel size and download speed. Also make sure the Constrain Proportions box is checked.
- If the image quality is not as good as you want, you can change the resolution quality from low to medium, or to high, under the Preset area of the box. You can also click directly on the Quality field and move the resulting slider left or right to increase and decrease the optimized size of the image. Just keep checking the quality of image itself and the resulting pixel size and speed. (Note: we’re focusing on the basics for resizing JPEG images; there are other presets in the box for PNG and GIF images.)
When everything is set, simply click Save, and Photoshop will resize the image based on your settings and save a copy of the image. The original image will not be saved.
There are also online options for resizing photos, but if you’re working in Photoshop, these basic methods should save some time. And if you find yourself resizing images for the web or for print, you might consider creating a Photoshop action or two to speed up the process.
Let us know how this tutorial works out for you, and if you have any questions or other suggestions.