3.1 CHOOSING IMAGE QUALITY AND SIZE

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The size of an image file and the quality of the picture it contains depend in part on the number of pixels in the image and the amount of compression used to store it.

Compression

To make large image files smaller and more manageable, digital cameras store images in a format called JPEG after its developer, the Joint Photographic Experts Group and pronounced "jay-peg." This file format not only compresses images, it also allows you to specify how much they are compressed. This is a useful feature because there is a trade-off between compression and image quality. Less compression, sometimes called Fine mode, gives you better images so you can make larger prints, but you can’t store as many images. More compression, in modes such as Normal or Basic, lets you store more images and makes the images better for making smaller prints, posting on a Web page, or sending as e-mail attachments. The only problem is that your prints won’t be quite as good. For the highest resolution, some cameras offer an uncompressed format.

Here, two versions of the same image have been enlarged. The image on the left is uncompressed. The one on the right is a compressed JPEG file.

Image size

In addition to offering two compression modes, many cameras let you also change image size as a way of controlling the size of image files. Because you can squeeze more 640 x 480 (VGA) images into a storage device than you can squeeze 1600 x 1200 images, there may be times when you’ll want to switch to a smaller size and sacrifice quality for quantity.