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In some cases, images are too large, and you need to reduce their resolution and physical size. In other cases, you might need a higher resolution to output your images at larger sizes. This method of sizing – changing the size, as well as the number of pixels – is dubbed resampling an image. Specifically, reducing resolution is downsampling, and raising resolution is upsampling.

Here’s a quick example to clarify the benefit of resampling. Say you have a photo taken with a digital single-lens reflex (SLR) camera, which takes pretty high-resolution photos. The photo could easily have a resolution of 300 dpi and dimensions of 14 x 10 inches. If you just want to make a few color corrections in Elements and then make 7-x-5-inch prints for your family members, resampling the file keeps the file size manageable for both your computer’s memory and for uploading to a printing service. Because you decreased the photo’s dimensions, the photo still maintains the resolution you need for a high-quality photo print (that is, 300 dots per inch; dpi). If you just changed the photo’s dimensions without resampling, the photo’s resolution would almost double, making for an unnecessarily large file.

Use caution when you resample images; when you resample, you either toss away pixels or manufacture new pixels. To protect your images during resampling, work on a copy of your image, instead of the original file.

Changing image size and resolution

You can change an image’s size and resolution in a couple of different ways. One method is cropping images. You can use the Crop tool with or without resampling images. For more information on using the Crop tool, see Chapter 9. Another method is using the Image Size dialog box, which you use in many of your editing sessions in Elements.

To resample an image with the Image Size dialog box, follow these steps:

1. Choose Image ⇒ Resize ⇒ Image Size.

Alternatively, you can press Ctrl+Alt+I (⌘ +Option+I on the Mac). The Image Size dialog box opens, as shown in Figure 2-2.

The Pixel Dimensions area in the Image Size dialog box shows the file size (in this example, 12.1M). This number is the amount of space the image takes up on your hard drive. The width and height values are fixed unless you select the Resample Image check box at the bottom of the dialog box.

2. In the Document Size area, redefine dimensions and resolution.

The options are

● Width: Type a value in the text box to resize the image’s width. Then press Tab to move out of the field and implement the change. From the drop-down list to the right of the text box, you can choose a unit of measure: percent, inches, centimeters, millimeters, points, picas, or columns.

● Height: The Height options are the same as the Width.

If you keep the sizing proportional, you typically edit either the Width or Height text box, but not both. When you alter either width or height, the resolution changes inversely.

● Resolution: Type a value in the text box to change resolution and then press Tab to commit the change. After you edit the resolution, the Width and Height values are changed inversely (if the Constrain Proportions check box is selected).

3. (Optional) If you’re okay with resampling your image to get the desired size, select the Resample Image check box.

With this check box selected, you can change dimensions and pixels at the same time, which results in either reducing or increasing the number of pixels. When the check box is deselected, the values for dimensions are linked; changing one value automatically changes the other values.

Before you resample your image, however, be sure to check out the following section, “Understanding the results of resampling.”

4. (Optional) If you select the Resample Image check box, choose a resampling method from the drop-down list below it and/or select the other resample options above it.

In the drop-down list, you find different choices for resampling. See Table 2-2 for details on each method.

When you select the Resample Image check box, the two check boxes above it become active. Here’s what they do:

● Scale Styles: Elements has a Styles panel from which you can add a variety of different style effects to images. (See Chapter 11 for details.) When you apply a style, such as a frame border, the border appears at a defined width. When you select the Scale Styles check box and then resize the image, the Styles effect is also resized. Leaving the check box deselected keeps the style at the same size while the image is resized.

● Constrain Proportions: By default, this check box is selected, and you should leave it that way unless you want to intentionally distort an image.

5. When you’re done selecting your options, click OK to resize your image.

FIGURE 2-2: The Image Size dialog box.

TABLE 2-2 Resampling Methods

Understanding the results of resampling

As a general rule, reducing resolution is okay, but increasing resolution isn’t. If you need a higher-resolution image and you can go back to the original source (such as rescanning the image or reshooting a picture), try (if you can) to create a new file that has the resolution you want instead of resampling in Elements. In some cases, upsampled images can be severely degraded. Regardless of whether you upsample or downsample an image, always save a copy of the photo under a new filename.

If you take a picture with a digital camera and want to add the picture to a web page, the image needs to be sampled at 72 ppi. In most cases, you visit the Image Size dialog box, select the Resample Image check box, add a width or height value, and type 72 in the Resolution text box. What you end up with is an image that looks great on your web page but still downloads quickly. In Figure 2-3, you can see an image that was downsampled in Elements from over 14 inches horizontal width.

FIGURE 2-3: Downsampling images most often produces satisfactory results.

If you start with an image that was originally sampled for a web page and you want to print a large poster, you can forget about using Elements or any other image editor. Upsampling low-resolution images often turns them into the sort of mush shown in Figure 2-4.

FIGURE 2-4: Upsampling low-resolution images often produces severely degraded results.

You might wonder whether upsampling can be used for any purpose. In some cases, yes, you can upsample with some satisfactory results. You can achieve better results with higher resolutions of 300 ppi and more if the resample size isn’t extraordinary. If all else fails, try applying a filter to a grainy, upsampled image to mask the problem. Chapter 11 has the details on filters.