More and more people are taking the plunge into digital photography, as higher-quality consumer cameras and photo printers become less expensive. Perhaps you’ve already leapt or are contemplating a digital camera purchase. Over the next few weeks we’ll take a geek-free “big picture” look at what you’re creating when you take the picture, how to manipulate and manage your pictures, what to look for in a digital camera, and some pitfalls to avoid as you build your digital photo library.

What happens when you take a picture with a digital camera? When the shutter opens, the light that comes through the lens is recorded on millions of photosensitive diodes called photosites. The data from each individual photosite is stored as a set of numbers that represent the color and brightness of the light recorded. That information defines each of the building blocks of a digital image – the pixel. Pixels (short for “picture elements”), are tiny squares that can each be assigned any one of 16 million colors. In a sense, a digital photo is a “paint by numbers” picture, comprised of individual pixels with the color and brightness recorded by each photosite.

Now, a tasty tidbit of useful information. You’ll see digital camera manufacturers touting their increasing number of “megapixels”. What’s that all about? The megapixel term refers to the number of photosites the camera has, hence the number of pixels it can record. For example, a 3 megapixel camera has an array of roughly 2000 x 1500 photosites (2000 multiplied by 1500 equals, you guessed it, 3 million, or “mega” pixels.

Now, once the picture is taken, the little computer in the camera organizes the data into an image. Each pixel in the image “weighs” about 3 bytes, so in the 3 megapixel example above, the image created would have a physical size of around 9 megabytes (MB). Given that most consumer cameras come with between 8 MB and 64 MB memory cards, that’s not many photos per memory card. Although some high-end cameras allow you to store images in this “raw” state (called, amazingly enough, the CCD RAW format), most consumer cameras apply some kind of compression to the image to decrease the file size.

There are two types of compression: lossless, and lossy (rhymes with “bossy”) referring to how much the image quality is degraded by compression. TIFF (Tag Image File Format) compression is lossless, but doesn’t result in a much smaller file size. The most popular compression format, albeit a “lossy” one, is JPEG. JPEG is named after the Joint Photographic Experts Group, the committee that developed the format. Here’s how it works. When JPEG compression is applied to an image, data that isn’t obvious to the viewer is removed. For example, if there is an area made up of a lot of green pixels, only the value of one green pixel is saved along with the locations of the other green pixels in the image. When the image is later viewed, it is decompressed, and the green pixels return to their former spots.

Remember, we’re talking about compression done on the image while it’s still in the camera. On many cameras, the amount of JPEG compression applied is selectable, so consider this: more compression, smaller file size, less quality. If you can afford the extra memory and can select the level of compression, I recommend taking the highest resolution photos with the least compression your camera will allow. Although you may have to spend more time transferring from your camera to your computer, you’ll have more flexibility as you move on to printing, emailing, or web posting your masterpieces for the world to see.

© 2003 Peter F. Zimowski