|About Digital Photography...
How High Is High?
In the early days of digital cameras (a mere three years ago), anything higher than 300,000 pixels on a sensor array was considered leading-edge technology. When Olympus came out with its by-now-classic D300L with 786,432 pixels, it was hailed as an achievement equal to breaking the sound barrier. Indeed, it was a significant advance, but today its just a tired old prop plane flying among jets cruising at 3 million pixels or more.
As a rule of thumb, you can figure that digicams with less than a million pixels will give you good 4 x 6 inch snapshots. But for larger prints, youll need 1, 2, or 3 MegaPixel cameras for prints 5 x 7, 8 x 10, and 11 x 14 inches respectively. This assumes, of course, youre not chopping a tiny piece out of the image and attempting to blow it way up.
But what if you dont want big prints? Well, then, you wont need a MegaPixel camera. If you just want drugstore-sized photos to be able to send images to friends and family through email (so they can enjoy looking at your pictures on their computer monitor), a lower resolution digicam will do just fine. You cant view high resolution on pictures on most computer monitors, anyway; theyre limited to displaying images in the neighborhood of 72 to 96 pixels-per-inch and low resolution digicams are just fine for that.
Whaddya Mean, "pixels-per-inch?"
You caught that, huh? Here weve been talking about resolution in "pixels" and then I throw in "pixels-per-inch." OK, lets digress for a moment. Digicam resolution is expressed in pixels because CCDs are different sizes. So you can have a 1/2-inch CCD with 640 x 480 pixels on it and a 1/3-inch CCD with the same number.
But when you print your image, you can make it smaller or larger by squeezing pixels together or expanding them. You do this in an imaging program where you tell it what size picture you want and it orders the pixels to cozy up or spread out. Since your photo size is in inches, less or more pixels will occupy the same space per-inch according to the image size youve chosen.
So lets say youve shot a picture at a resolution of 640 x 480 pixels. If you want a 4 x 3 inch photo, it will print out at 160 pixels-per-inch. (640/4 = 160 and 480/3 = 160). On the other hand, if you want to make your picture larger, say, 8 x 6 inches, those pixels will have to become bigger and only 80 of them will fit in the same inch of space.
Since only 80 pixels of picture information are occupying the same real estate that 160 used to fill, you might begin to see each one (or at least jagged edges on objects) because theyve become big enough to notice. If there were more pixels (higher resolution) to begin with, they could spread out to give you a bigger print, yet each one would be able to stay small enough to be invisible to your eye.
Incidentally, you may sometimes see pixels-per-inch (abbreviated ppi) referred to as dots-per-inch (dpi) but thats the wrong way to describe them. Dots are what ink-jet printers use to reproduce each pixel and the two terms have totally different meanings. A printer with a high resolution (like 1440 dpi) cannot make up for a lack of pixels in your image. It can only do a better job of reproducing the color and definition of each pixel than if it were set to, say, 360 dpi. So now you know.
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