Dealing with digital images, Part 5: Coping with the huge files scanners create

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So what can you do? Add storage and learn how to save secondary copies of images as JPEGs.

technofile
Al Fasoldt's reviews and commentaries, continuously available online since 1983

Dealing with digital images, Part 5: Coping with the huge files scanners create

Feb. 27, 2000

By Al Fasoldt
Copyright ©2000, Al Fasoldt
Copyright ©2000, The Syracuse Newspapers

   You might already know that you don't need a digital camera to create your own computer-based images. All you need is a scanner.
   In just a few minutes, a good scanner can turn a picture of the kids into a digital image that you can show on your computer screen. And you can quickly turn that image into desktop wallpaper or send it to all your relatives by e-mail.
   But beware: Unless you're careful, images you scan can be too big to send in the mail. They can also be too big to fit onto a floppy disk -- something you need to know if you're still using floppies to cart around the family snapshots.
   The problem isn't just how big you make your scans. It's also how much they are compressed. Images you see on your screen are nearly always squeezed in one way or another. This makes them smaller, but it can cause problems of its own.
   Programs that compress images do it in two different ways -- by preserving the image perfectly, so that it can be uncompressed and restored to exactly the same appearance, or imperfectly, by removing parts of the image to achieve greater compression.
   Perfect image compression is called "lossless" compression. A simple method of achieving "lossless" compression would be to represent repeated areas mathematically, so that 500 horizontal spaces in the picture made up of pure white could be stored as "500Hwhite," to give an overly simple example.
    Imperfect compression is known by a made-up term, "lossy compression." In "lossy compression," parts of the image (especially areas where there is a lot of detail) are removed or simplified. The most common form of lossy compression is JPEG, also known as JPG. (Trivia fans might want to know that the acronym stands for "Joint Photographic Experts Group.")
   JPEG compression handles photo-quality color rendition -- what Windows calls "true color" and the Mac calls "millions of colors" -- and it's able to squeeze images quite a bit. You can sometimes reduce an image to 1/7th of its normal size without much harm using JPEG compression.
   JPEG images can fool you, so listen up: A JPEG image that is, say, 200 kilobytes in file size is NOT that size when you view it. It expands into your computer's memory to take up its full, uncompressed size. (That's one reason your computer needs a lot of memory to deal with big images.)
   The most common form of "lossless" compression is the GIF format, but GIF has two big drawbacks -- it normally doesn't handle more than 256 colors and it uses a disputed method of compressing images.
   The 256-color limit is enough to keep GIF from consideration when you're saving your scanned images, since you'll always want photographic images to have millions of possible colors. (They'll look horrible otherwise. Don't even think of using anything but True Color or "millions of colors" if you care about picture quality.)
   The GIF dispute came about because Unisys, the company that created part of the GIF method, requires royalty payments when GIFs are used commercially. Many Web sites are removing GIFs and replacing them with another image format called PNG (Portable Network Graphics).
   A third format that's very common in Windows is BMP. This stands for "bitmap," computer jargon for a kind of paint-by-the-numbers scheme. Bits are "mapped" by X-Y coordinates, more or less.
   BMP images are used for wallpaper. But they're perfect for storing everything you scan, too, because they're not compressed at all. You can use other methods, too -- Mac users might prefer the TIFF format, for example, as long as they turn off all TIFF compression -- but stick with BMP and you'll be happy.
   Why should you care about the image format? Why not just save the image in a highly compressed form to save disk space?
   That wouldn't be smart. The image you create when you scan a picture should be considered the "master scan" -- the image file that you should squirrel away somewhere so that you'll always have a digital copy of everything you've scanned. (In my family, my brother Bob has scanned hundreds of old portraits, for example, and he makes sure the scanned images are all stored safely on backup disks so that we'll always have them if the originals get lost or damaged.)
    Check to see what choices your scanner software gives you when it saves an image. My scanner software doesn't give me a choice at all until I "export" an image, so you might a similar situation. (Jargon never dies. "Export" just means "save," right? I wonder if the folks who write software "export" their paychecks when they take them to the bank?)
   But if you follow my advice, you run into two problems right away: Images you save can tend to be immense and therefore hard to store, and you won't be able to show off these great digital images by sending copies by e-mail because they'll be too big to send. (Most Internet Service Provider limit the size of all e-mail attachments so they won't be swamped with multi-megabyte mail files.)
   So what can you do? Add storage and learn how to save secondary copies of images as JPEGs.
   My choice for added storage for images is a CD-ROM recorder, also called a CD "burner." Every other method of adding storage (Zip drives, LS-120 drives, and many others) is much more expensive. CDs cost about $1.40 per gigabyte; Zip disks cost about $120 per gigabyte. If that doesn't keep you away from Zip drives forever, you've got to be rich.
   As for saving secondary copies, just get one of the image viewers or image editors I wrote about earlier and open the BMP version, then save it with another name as a JPEG file. Please note that renaming the file from BMP to JPEG (such as "myphoto.bmp" to "myphoto.jpg") does not change it from one format to the other. Renaming merely renames the file. You have to use "Save as" in the menu of the software and choose JPEG.
   A warning: Windows users who want to send photos by e-mail to Mac users should send a small test photo first to make sure the Mac users can view the pictures. JPEGs won't be a problem, but the file-attachment method might be. This is especially irksome if people with normal Internet connections are sending to AOL users. (AOL's entire online system is poorly suited to attachments except within AOL.)