Digital Focus: Scanners for Photographers

Feature: Getting Started With a Photo Scanner

Every time technology changes the way we store memories, our old collections are at risk of being lost in the shuffle. When CDs replaced LPs, many of us had no way to listen to our treasured Humble Pie and Pretty Things records. With VHS steadily transitioning to DVD, I'm sure you're worried that you'll have no way to watch your collection of Star Trek and The Prisoner episodes. And now that 35mm film is starting down that same path thanks to digital photography, even our precious slides and negatives might become orphans.

One way to preserve your old photo collection is to get a scanner and use it to deliver your negatives, prints, and slides into the digital age. Not only does a scanner let you save those old pictures, but you can breathe new life into them as well. A scanner lets you share old, fragile pictures with friends and family--and perhaps even restore them digitally. Interested? This week, let's talk about scanners and how to shop for them.

Understanding Scanners

In many ways, a scanner is really just a digital camera--but instead of capturing the entire scene in a fraction of a second, a scanner methodically scans a line at a time as the CCD (short for "charged-coupled device"), which serves as the "eye" of most scanners and digital cameras, moves across the scanner's platen, or scanning bed. Indeed, a scanner's resolution is measured, in part, on the accuracy of the motor that steps the CCD across the platen.

What kind of scanner should you get? Flatbeds are typically the most versatile. Not only do they make high-quality images of photos and other documents, but they accept options like automatic sheet feeders that enable you to conveniently scan many pages. They can also scan almost any size document, from tiny business cards and 35mm slides all the way up to letter- or legal-size documents. Microtek's top-rated 2400-dots-per-inch ScanMaker 4900, for instance, can be found at the PCWorld.com Product Finder for as little as $130.

The major limitation of flatbeds, at least as far as we photographers are concerned, is that they usually lack the resolution to make good enlargements. They can also make poor scans of slides and negatives, even if you have a special adapter. I'll tell you why later, when we get to the section on dynamic range.

Personally, I use a film scanner. They are expensive, and vary dramatically in price, starting from about $500 at the low end to several thousand dollars at the high end. However, they deliver outstanding results. Film scanners are designed to accommodate slides and negatives and can usually reproduce pictures at a very high resolution--as much as 4000 dpi--which gives you rich, detailed digital images that you can print at full enlargement sizes. I love Nikon's 4000-dpi Super Coolscan 4000ED, for instance, which I found for $1069 at our Product Finder.

More on DPI and Bits

Like cameras, scanners are rated by resolution. Scanners, though, have two resolutions, such as "600 by 1200 dpi." The first number is the optical resolution of the imaging system; the second is the resolution of the step motor that moves the scanning head across the document. Since the optical resolution is always lower than the number of discrete steps the motor can perform, the first number--the actual resolution of the optics--is more important. You should rely on that number to compare scanners.

You also need to think about color depth. Some inexpensive scanners are 24-bit devices, meaning they can capture 16.7 million colors, which is near the number of colors that the human eye can see. More sophisticated scanners work at 30, 36, or even 42 bits per pixel, which translates to billions of colors. Scanners with more than 24-bit accuracy have more colors to choose from when resolving dark regions and images with lots of rapid color changes. This adds up to a high-quality image. If you are serious about scanning your photos, keep an eye on color depth and choose your scanner accordingly. If you're scanning snapshots or posting images on a Web site, color depth isn't as important.

One other point to remember: Some scanners cannot save images at their maximum rated color depth. These units can do high-bit scans, but their drivers may have to resample the data and convert each image into a smaller lower-color-bit file for saving and using.

Making Sense of Dynamic Range

The concept of dynamic range is a bit complex, so a lot people often skip the topic entirely. When scanning slides and negatives, though, I'd say that dynamic range is more important than the scanner's color depth--so it's worth considering. A scanner's dynamic range is a measure of how well the device can record changes in the brightness of the image it's scanning. It's measured on a scale from 0 to 4, where 0 is pure white and 4 is almost pure black.

The higher the scanner's stated dynamic range, the better it is at discerning shadows and subtle changes in dark colors. Every whole number change in dynamic range is a tenfold increase or decrease in light intensity: For example, a scanner that has a dynamic range of 4 is sensitive to a 10,000:1 range of light intensity in the scanned image.

So who should care about all this gobbledygook? Anyone who scans slides and negatives. Only film scanners have sufficient dynamic range (3.2 or higher) to make satisfying scans from film. Slides and negatives store a very deep dynamic range and you'll want a film scanner to have the best dynamic range you can afford, else you'll lose all the details in your shadows and darker image regions.

For more on shopping for a scanner, see "How to Buy a Scanner."