CYBER NOTES May, 2006 by Dave Benore

IMAGE FILE TYPES -- TIFF vs. JPEG

Last month I talked about the difference between text and graphics files. Guess what kind of files your digital camera generates? They are graphics, of course, called image files in the case of a camera. Remember that file names have extensions, like .doc for Word data files and .xls for Excel data files. Common image files have filename extensions like tif, jpg, or gif, to name a few. GIF is not normally used by cameras.

These filename extensions identify different schemes of coding computer ”bits” that represent a picture or a graphic. A digital camera takes a picture by recording the light that falls on each picture element, or “pixel”, in the camera. Each pixel has typically 12 bits of information associated with it that describe color, brightness, etc. The collection of all these bits is called a “RAW” file, meaning unprocessed.

The camera then normally converts the RAW file into another format. This other format typically would be a TIFF (.tif) file or a JPEG (.jpg) file. The .tif or .jpg file would then be downloaded to a computer at a later time. (Some cameras can download RAW files without doing a conversion.)

JPEG stands for Joint Photographic Experts Group and TIFF stands for Tagged Image File Format. TIFF was designed to become an industry standard for image file exchange. TIFF files can be read by either PCs or by MACs. JPEG files are compressed to a smaller size than TIFF files so as to use less hard disk space; and they move over the Internet quicker. TIFF files can be compressed also but still are usually much larger than JPEG files of the same image.

Files are compressed by different schemes and by different amounts. With image files, any compression results in the loss of some data. The more compression used, the more data lost. Normally the loss is not perceived by the human eye unless it gets severe. However, repeatedly saving an image file as a JPEG can, with each save, make the file smaller and lose more data. After several repeated saves, the human eye can detect the degradation of the image. If you plan on editing an image, save the image as a TIFF file if you can, then do the editing, and then save the edited file as a JPEG if you wish to save space on your hard disk. The bottom line:

TIFF files contain more data—are more accurate—than JPEG files.

TIFF files are usually much larger than JPEG files.

Use JPEG for ordinary photos and those you send over the Internet.

Use TIFF format for large blow-ups to preserve details after enlarging.