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Focusing on Digital Cameras, Part 1: Higher Is Better

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There's nothing more thrilling than shooting pictures with a digital camera and then - with hardly any steps in between - seeing them splash onto your computer screen and flow smoothly into your image editing program. It's the same as watching the birth of a photographic print in a developer tray, or experiencing the chills that accompany unwinding still-wet negatives from a reel and holding them up to the light.

Of course, if you need a reason other than "it sounds like fun" to have one of these new magic machines, consider the following advantages: instant images, no scanning, no film costs (which encourages creativity), and promoting a cleaner environment. There's also the historical significance of being among the first pioneers to venture into new photographic territory. Whatever your motivation, this article will acquaint you with the basics of digital photography.

In this two-part series, I'll first discuss resolution and general issues such as light sensitivity that relate to using a digital camera. Next week, I'll cover specific issues to consider before purchasing a digital camera, and offer my opinion on the best cameras currently available in the low to middle price range. For now, begin your quest for the right digital camera by asking yourself how you'll use the pictures; those uses play heavily into what features you'll need from a camera.

Resolution for the Screen -- No discussion about digital cameras and imaging can avoid the subject of resolution. Many chapters have been written about resolution, but I'll try to make it as simple as possible. If you're not up to tech-talk now and want to skip the next few paragraphs, remember this: when discussing digital camera resolution, "Higher Is Better." Memorize that and you'll ace Resolution 101.

Before we launch into screen dimensions and measurements, let's make sure we're all talking about the same thing. Images from digital cameras (and scanners) are made up of little squares (sometimes rectangles) called pixels. Pixel is short for "picture cell" or "picture element." Pixels also make up the images on a computer screen. Printers, in contrast, produce images by laying down many little dots on a piece of paper.

Digital pictures and monitor screen images are measured in pixels-per-inch (ppi). Printer output is measured in dots-per-inch (dpi). Many people interchange the two abbreviations (especially when discussing scanning) which drives some purists insane. For clarity, it's best to use ppi and dpi as separate terms.

If a digital camera records a picture that has 640 by 480 ppi, the camera's resolution is determined by old-fashioned multiplication: 640 times 480 equals 307,200 pixels.

Suppose your digital camera records pictures at a default measurement of 640 pixels wide by 480 pixels high. To figure out how big such an image will be on your computer monitor, a bit of division is required; for instance, on most Mac monitors, 72 pixels in a row equals a linear inch. So to find out the length - in inches - of 640 pixels, just divide 72 into it and you get 8.8 inches (about 22.4 cm). Do likewise with the short side of 480 pixels, and you end up with 6.6 inches (about 16.8 cm).

Given that 8.8 by 6.6 inches is a pretty good size, if you don't plan to print images, a 640 by 480 ppi resolution should work nicely. It even gives you a large enough image that you can remove unwanted elements and still have a good chunk left over for viewing.

Resolution for Printing -- However, if you want to print that photo on paper, things change drastically. You certainly can print that same 640 by 480 ppi picture as an 8.8 by 6.6 inch photo, but you may not be satisfied with the results. It depends on how fussy you are about picture quality. The picture might look fuzzy or have jagged edges - called pixelization, a phenomenon that occurs in low-resolution pictures when there aren't enough pixels to describe the range of color or detail in an image.

As a quick fix, you can tell your imaging program to interpolate the image, that is, to add more pixels, thus increasing the ppi count. Interpolation adds more pixels in order to make the image look smoother, but the results are not always satisfactory because the program must guess where to insert extra pixels, what color they should be, and so on. To get the image quality you want, it's often necessary to reduce the image size; this pushes the existing pixels into a tighter fit, resulting in higher overall resolution and a more pleasing picture.

Right about now you may be thinking: "My color ink-jet printer can give me all the resolution I need, because it can print at 720 dpi - it says so right in the manual." Well, yes, but what the manual means is that the printer is capable of squirting a maximum of 720 dots of ink per inch, with an average of three dots of ink assigned to print each pixel. (Remember, pixels and dots are not the same!)

If you have a 640 by 480 ppi image whose size is 8.8 by 6.6 inches, that image will have 72 pixels per inch and your printer will spit out about 216 ink dots per inch (3 dots of ink for each pixel multiplied by 72 pixels equals 216 dots of ink).

Since you paid for 720 dpi and got only 216 dpi you might think a hefty refund is due. Not so fast. You can print that picture at 720 dpi if it is reduced in size so its pixels scrunch together to line up 240 of them in an inch of space. Then, with each pixel getting 3 dots of ink, your printer would be outputting its full potential of 720 dpi. (Sorry, no refund.) In order to pack pixels in that tightly, the original 8.8 by 6.6 inch image must shrink to 2.6 by 2.0 inches (6.6 by 5.1 cm), making it a great size to frame as a dollhouse painting.

However, take heart. The 3:1 shrinkage ratio that we end up with is an extreme that may not be necessary. You can get fine pictures at 4.4 by 3.3 inches (by pushing the pixels together to 144 ppi), and even good 8.8 x 6.6 inch prints at their original 72 ppi. Of course, if you started with a higher camera resolution of 1,024 by 768 ppi you'd get excellent 7.1 by 5.3 inch (18 by 13.5 cm) prints at 144 ppi. You can even get acceptable 14.2 by 10.6 inch (36.1 by 26.9 cm) photos at 72 ppi if you're going to be looking at them from a short distance, since viewing distance has a lot to do with what an image looks like. For example, did you know outdoor billboard images are printed at only 18 dpi? They look great, but only at the right distance.

What all this math boils down to is this: higher is better when it comes to digital cameras. Buy a camera with as high a resolution as you can afford if you want to make reasonably-sized prints. Most cameras offer a choice of high and low resolution modes, but chances are good you'll use the higher one most of the time.

Higher Is Bigger, Too -- Of course, the higher the resolution, the larger the file size - even though most images are compressed in the camera using JPEG (Joint Photographic Experts Group) encoding. At first, you'll probably want to save every gem you've shot, so expect your hard disk to fill up fast (another reason to buy a removable drive, with plenty of cartridges).

Your file sizes will depend on the specific image and the degree of compression you choose (user selectable in many cameras). Figure that an uncompressed image will be roughly five to twenty times larger than its compressed size. A 640 by 480 ppi image compressed to 50K will inflate to about 900K when opened in an image editing program. A 1,024 by 768 ppi image compressed to 200K expands to 2.25 MB. And when you get to 1,280 by 1,024 ppi (the highest resolution in the $250 to $1,300 price range I'll be looking at) a 900K JPEG balloons to 3.75 MB.

That's only the beginning. If you do any editing on images, you won't want to save them as JPEGs, because JPEG is a lossy compression method. This means that to reduce file size, some of the image information is lost; once gone, you can't get those pixels back without starting over from your original image (which you saved before doing any editing, right?). Instead, you'll likely save images as TIFFs (Tagged Image File Format, which can employ LZW lossless compression in some image editing programs) or as uncompressed PICTs. (For more information on image file formats and compression, see NetBITS-007.)


Patience Is a Plus -- Let's take a little breather here. I live with several cats and I'm always telling newlyweds to have cats before they have children (a biological impossibility, but you know what I mean). Cats teach you how to be patient and accept things on their terms. So will digital photography. If you love instant gratification, it will certainly provide you with that, but it will also teach you patience.

The first time I transferred images from a digital camera through the Mac's serial port to my hard disk I was too excited to notice each one took about 30 seconds. Doesn't sound like much, but when you transfer 40 exposures, that's a minimum of 20 minutes. Plus, it takes still more time to rotate those vertical shots upright so you don't twist your neck out of shape.

Then, once transferred, you must separate the good, the bad, and the ugly. So far, there's no easy way to do this. The "digital contact sheet" displayed prior to downloading isn't - as they say where I live - worth spit. The images are too small and you can't see detail. So, expect to end up transferring most of them. And when they're finally aboard, it's not easy to position them side-by-side onscreen without resizing them and fiddling even more.

To help a little, there's a great freeware program called Jade 1.2 that will let you drag & drop a folder of images onto its icon and bring the pictures up in various sizes - tiled or stacked. It can't yet turn those verticals right side up, alas.


All this will change, of course. You'll eventually be able to transfer scores of images in a flash (literally) and software will eventually take care of positioning and selection. But for now, prepare to have your patience tested.

Imaging Software -- You'll need a photo imaging program to transfer and work with the images. Most camera manufacturers supply plug-ins to simplify this process. Adobe's cross-platform PhotoDeluxe is bundled with many cameras. I prefer PhotoFix, which is called PhotoStudio when it's bundled. It has 32 levels of fast undo-redo which cuts the learning curve to next to nothing, and makes it a snap to do traditional photographic darkroom stuff without spending a fortune on workshops and seminars. You can also opt for the big gun of photo-imaging, Adobe Photoshop, but for hobbyist digital camera owners, it's way too much power (and expense).

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Light Sensitivity -- Unlike conventional cameras where you can select films with different sensitivities to light, digital cameras in the under-$1,500 price range have only one fixed sensitivity to light, usually a film-equivalent ISO of 50 to 200. It's not a big limitation, though. Many of them take good pictures under low light conditions because their lens apertures are pretty fast, usually around f-2.8. As a standard feature, most have a built-in flash for abysmal conditions and for filling in deep shadows on sunlit, high-contrast subjects. And when it comes to freezing action, some even have shutter speeds up to 1/10,000 of a second!

What you may find disconcerting at first is the slight lag time that occurs between pressing the shutter release and the actual exposure. That's when the camera spends a fraction of a second going through its pre-shot calibration and white-balancing act. There's also some delay between shots while the camera processes and compresses the image, and some people miss the whirring sound of film being advanced. You'll quickly adjust to these quirks, though.

You've Come a Long Way -- Civil War photographers like Brady and O'Sullivan had to sensitize their plates with poisonous solutions in a dark tent, then shoot their picture before the emulsion dried. That was a real hassle, but the thrill of the results made it worthwhile. You'll feel the same way once you get into digital photography, I guarantee (without handling poisons, even).

Next week, I'll tell you what I consider to be the eight best digital cameras in the $250 to $1,300 price range.

[Arthur H. Bleich has been a photographer, writer, filmmaker, musician, and teacher. He currently serves as the Executive Director of The Children's Telemedical Health Fund, which provides free medical and psychological care to needy kids through interactive television.]



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