Digital Focus: All About Pixels and Resolution

Photo quality and jaggies, plus how many pixels is enough?

Dave Johnson

Feature: Digital Photo Basics--Pixels and Resolution

For years, digital camera makers have been chasing a fixed target: the quality of traditional photographs. Since digital cameras create pictures made from pixels--lots and lots of more-or-less square picture elements--the trick has been to reach a point where digital cameras can capture enough pixels to duplicate the effect of film. Are we there yet? Kind of.

One of the first questions new digital photographers often ask me is "What's the resolution of a 35mm picture in pixels?" Unfortunately, that's a really hard question to answer. Film is essentially thin plastic covered by a soup filled with millions of grains of silver halide. A 35mm picture doesn't have pixels. When you enlarge a film-based photo past its optimum size, you don't see square blocks like you do in digital photos: You see soft-edged, fuzzy grains.

The issue is further complicated by the fact that 35mm resolution varies dramatically based on the kind of film (for example, slides are sharper than prints), the ISO (the lower ISO rating, the smaller the grains), and even the lighting conditions and exposure (optimum lighting yields sharper pictures than badly exposed or long-exposure shots).

With all those variables, can the question even be answered? Sure, as long as you don't mind a big range of options. Typically, 35mm photography generates pictures that have the equivalent of between 6 megapixels and 20 megapixels. A megapixel, the standard by which digital cameras are sold, is a million pixels--so a 1280-by-960-pixel image is 1 megapixel.

So we're there! The bottom line is that many increasingly affordable digital cameras in the 5 or 6 megapixel range can give you essentially the same quality that you get with a point-and-shoot 35mm film camera loaded with 400 ISO print film.

How Many Pixels Do I Need?

That said, there's still a bigger question: What resolution do you need? The real question is this: What do you intend to do with the photo after you take it? If it's headed for e-mail, the Web, or a slide-show application, then you only need a megapixel or less. If you want to send the photo to your ink jet photo-quality printer, then you'll need about 200 or 250 pixels for every inch you want to print. An 8-by-10-inch print, then, should measure about 2000 by 2500 pixels. You can send a smaller image to the printer, but if you skimp on pixels you'll probably see jaggies in the final print.

Don't read those guidelines and think that I'm recommending you shoot your pictures in lower resolutions. Sure, your digital camera has a variety of resolution settings, but I suggest that you set your camera to its highest resolution and leave it there. Why? Because that way you can crop your photos and still have enough resolution for sharp-looking prints.

Think of your image editor as a sort of after-the-fact zoom lens. With megapixels to spare, you can inspect your photo on the PC and cut away the extraneous, the distracting, and the unneeded. You're left with a tight, impressive photo that you can print or process however you like. If you throttle down the camera's resolution to begin with, the image will have only enough pixels to print sharply if you don't do anything to the image. Cut away half the picture to eliminate a distracting object on one side of the scene, though, and now you'll have to "stretch" the image to print it at the same size. The result is that your image will look jagged, blocky, and blurry. Remember: In digital photography, more pixels are always better than less.

Dave's Favorites: Personalize Gifts With Club Photo

Once there were dozens of online photo-sharing sites, but the dot-com crash whittled the number down to a handful. Club Photo is one of the survivors, and I think it's one of the best. For a small subscription fee ($25/year) you can create as many as 20 separate online "albums" packed with photos for friends and family to share.

In the past year, I've started to take advantage of some of Club Photo's other services, like exotic baked goods, poster-size enlargements, and personalized gifts. I can't recommend them enough.

Take, for instance, the Photo Cookies. I ordered a batch of these for my best friend recently and had his newborn son's picture plastered on the top in edible frosting. By all reports, the family loved the cookies. Another time, I had a photo made into a huge 20-by-30-inch glossy poster. Another gift hit.

You can also order photo mugs, mouse pads, jewelry, and clothing. The bottom line? If you have a collection of digital photos and access to the Club Photo Web site, you've always got some cool gifts right at your fingertips. Bookmark Club Photo today--you'll thank me the next time a birthday rolls around.

Q&A: The Best File Format for CD

I'm scanning my father's slides and saving them onto CDs. Since I do not know what the others in the family will want to do with them, I want to save them in a format that leaves the most options. I have been saving them as bitmap files, which are very large. Is that the best bet?

--Mae Watson, Green Bay, Wisconsin

You're not alone in wondering about file formats, Mae--I get this question all the time. In fact, the bitmap file format has been largely abandoned for precisely the reason you cite: it's big. There's no data compression at work to reduce file size. It was originally used in earlier versions of Windows for smaller images like "wallpaper" files.

Your best bet is to use the JPEG format for photos. JPEG preserves virtually all of the image quality, is very compact, and is readable by every kind of computer and image program.

Hot Pic of the Week

Get published, get famous! Each week, we select our favorite reader-submitted photo based on creativity, originality and technique. Every month, the best of the weekly winners gets a prize valued at between $15 and $50.

Here's how to enter: Send us your photograph in JPEG format, at a resolution no higher than 640 by 480 pixels. Entries at higher resolutions will be immediately disqualified. If necessary, use an image editing program to reduce the file size of your image before e-mailing it to us. Include the title of your photo along with a short description and how you photographed it. Don't forget to send your name, e-mail address, and postal address. Before entering please read the full description of the contest rules and regulations.

This week's Hot Pic: "Wigwam Reservoir," by Dale Gangloff, Thomaston, Connecticut

Dale says he shot this photo in Thomaston, at a reservoir where the dam and building were built in the 1930s as a public works project. "I took this in the early morning with the light hitting the walkway and building," he says. "I was pleased that the fog coming from below showed up so well in the photo."

We want your feedback! Send your comments, questions, and suggestions about the newsletter itself to comments@bydavejohnson.com. If you have a question that you'd like to see answered in the weekly Q&A, send it to question@bydavejohnson.com.

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