Compressing and Shrinking Image Files

Adapted from Microsoft Windows XP Inside and Out, Bott, Siechert, and Stinson, Microsoft Press, 2001

When you initially capture or scan an image, the size of the file can be enormous. That's all well and good if you have a large hard drive and you intend to send the digital photo to a color printer using high-quality paper. The larger size means more detail and thus a better image. But large file size is a serious hindrance if you plan to send an image as an e-mail attachment or upload it to a Web site. In either of those cases, your most important consideration is reducing the image to a size that can be conveniently downloaded without sacrificing quality.

Shrinking Images for E-Mail

If you plan to send digital photos to a co-worker, friend or relative via e-mail, you'll run into problems if you don't plan carefully. If the recipient has a dial-up Internet connection, for instance, they probably won't appreciate tying up the line for a half-hour as your 6-MB attachment in TIFF or BMP format trickles in. With some Internet service providers (ISPs), attachments over a specified size are summarily rejected or can exhaust the user's quota on the server, causing all incoming messages to be rejected until he or she downloads your attachment.

If you manually attach an image file to a message, Microsoft Outlook Express, Outlook 2000/2002, and other e-mail client programs will send the original, uncompressed image. However, Windows XP can help you shrink the size of the image and convert the file to a compressible format, if you use the right technique. To do so, follow these steps:

Open a Windows Explorer window and select one or more picture files.
Click the E-Mail This File link in the File And Folder Tasks pane. If you make multiple selections, the wording of this task link changes to apply to the selected items or to all items in a folder. (If this option isn't visible, right-click the selection and choose Send To, E-Mail Recipient from the shortcut menu.)
In the Send Pictures Via E-Mail dialog box, the Make My Pictures Smaller option is selected by default. Click the Show More Options link to display the expanded version of this dialog box, as shown here.

By default, this option converts BMP and TIFF images to JPEG format (because GIF and JPEG images are already compressible, using this option leaves those file formats alone). It then compresses the file substantially and resizes the image to 640x480 pixels. If you're willing to accept a larger file size in exchange for more detail, you can select the Medium (800x600) or Large (1024x768) options instead.

Make a selection and click OK. Windows opens your default e-mail program, creates a new message, and attaches the compressed image file(s).
Add message text, insert the recipient's address, and click the Send button without worrying that you'll be overloading someone's Inbox.

The results of this compression can be startling. The table below shows the before and after file sizes of four images. In all cases, the compressed file is less than half the size of the original, and in the case of large TIFF and BMP files the compression ratio is as much as 99%.

How Compression Affects Graphics File Sizes

Original Picture Specifications

Original Size and Format

Compression Small (640x480)

Large (1024x768)

Scanned text document (B&W, 150 dpi, 81/2x11 inches)

268 KB

JPEG

36 KB

JPEG

126 KB

JPEG

Scanned magazine page (grayscale, 150 dpi,

81/2x11 inches)

1.11 MB

TIFF

16 KB

JPEG

(text unreadable)

85 KB

JPEG

(text readable)

Color photo from digital

camera (24-bit color,

192 dpi, 1280x960 resolution)

556 KB

JPEG

56 KB

JPEG

235 KB

JPEG

Scanned color photo

(24-bit color, 300 dpi, 3x5 inches)

6 MB

BMP

12 KB

JPEG

66 KB

JPEG

Caution

Using this technique to shrink and compress an image file invariably causes a loss of data. When you're sending a snapshot to your parents, the drop in quality is probably a fair tradeoff for the faster, slimmer e-mail attachment. But if the scanned image contains text, or if the recipient wants to be able to print a high-quality copy, check the compressed image before you click Send. Where quality is crucial, you might have better results using the Zip format to compress the original file without losing any data.

Compressing Batches of Image Files

Windows XP doesn't include any batch conversion tools to help you manage image files, but you can accomplish the same goal indirectly, by running images through the wizard used to shrink them for e-mail. If you're getting ready to upload a folder full of scanned photos to a Web site, for instance, you might want to convert them to JPEG format and shrink them to a standard size first. Here's how:

Open a Windows Explorer window, navigate to the folder that contains the images, and then select one or more files.
Click the E-Mail The Selected Items link in the File And Folder Task list,or right-click the selection and choose Send To, E-Mail Recipient from the shortcut menu.
In the Send Pictures Via E-Mail dialog box, choose the image size you want (Small, Medium, or Large), and click OK.
A new mail message window opens. Don't bother adding an address to the resulting e-mail. Instead, open a new Windows Explorer window and browse to the folder where you want to save the compressed files. (Don't use the original folder.)
Select all the attachment icons from the e-mail message, and then drag them out of the message window and into the folder you just opened.
Close the message window. Your files are now ready for uploading.