Terms of imaging

Computer Life column for January 31, 1998 by
Richard Gordon

Lately, maybe because the weather is chilly, I've been receiving a lot of e-mail from readers.

One reader wrote that she often feels she needs to "read a computing dictionary just to keep up." Here are three on-line computer-terminology dictionaries to help you decipher my column and otherwise impress the neighbors:

• The Free On-Line Dictionary of Computing, a joint project between several universities, with mirror sites all over the world (e.g., nightflight.com/foldoc/);

• Eric Raymond's Jargon File Resources (www.ccil.org/jargon/index.html), on-line cousin of The Hacker's Dictionary;

• whatis.com's dictionary of Internet terms (whatis.com).

Someone else sent in this plea: "What's the deal with e-mailing pictures? Do I need to shrink the picture and does the recipient need to zoom it? Does it take as long no matter how big the file is when you save it? What determines how many Ks, the size of photo upon saving it? Or content altogether? Help!"

Graphics files, no matter what format, contain information about each pixel, or smallest individual "dot," that together make up the image. The more information that's stored about each pixel, the larger the computer file that represents the image will be. For example, a "16-bit" file, in which the colors for each pixel are represented by 16 tiny chunks of data, will be a larger file than an "8-bit" file. However, since the 8-bit file contains less information about the image, the image will be of lower quality.

Then there's the "resolution"-how many of these dots or pixels are there per inch? The greater the resolution, the more "dots per inch" (dpi), the better quality the image will be. But again, this will drastically affect the size of the computer file. Most computer screens display images at 72 dpi. Therefore, unless you are preparing an image for a fancy printing job, choose 72 dpi as the resolution of images you send via e-mail.

The dimensions of the graphic also affect the size of the computer file since a larger image contains more pixels, requiring the file to have more information.

Once you reduce the size, the resolution, or the number of bits of color data, it's nearly impossible for the recipient to recover the image quality you surrendered to save space.

When I use, for example, Adobe Photoshop and an image scanner to convert a photo to a computer file, I usually retain the original file, even if it's enormous, so I can always start work with the highest quality original. Sometimes, I'll save a TIFF or PICT file, two high-quality image formats that do not require me to use Photoshop to manipulate the image.

But TIFF or PICT files are big and not universally understood. Therefore, I usually convert images into JPEG format (compressed, but still excellent quality images) or CompuServe GIF format (more compressed, therefore, only good quality images). For example, if my original Photoshop file is 1.5M, the TIFF file may be 1.4M, the JPEG 360K, and the GIF 188K.

GIF and JPEG files are nearly universal image standards. If I knew the recipient could read it, I could also save my file in Microsoft Windows' BMP format. JPEG, GIF, and some BMP files save space by reducing the amount of information stored about each pixel and, often, by reducing the resolution, the number of pixels per inch.

To send the image, you "attach" the picture to an e-mail message-that is, you send it not as part of the e-mail message but as something associated with it. In effect, the e-mail message acts like a cover letter and the attached file is like an accompanying package.

The size of the combined mail message and attachment can sometimes slow down delivery-but usually not by more than a few minutes.

How to view attachments you receive is a different story. Besides, I know I've lapsed into compuspeak. Thank heavens I included those on-line dictionaries so you can look up some of the terms.

Copyright © 1998, The News Journal Company

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