Like most other people who are into computer graphics, digital cameras fascinate me. They seem amazingly high-tech and come in a wide variety of shapes, sizes, capabilities and prices. Many of the high-end digital cameras mimic the styling of their film counterparts, while the consumer versions are becoming more and more far out in their design. There is a lot of confusion among consumers looking at this panoply of choices. The manufacturers tout various specifications, but the one they focus on most is the mysterious megapixel.
Simply put, a megapixel is one million pixels. Mega is the Greek word for great and a pixel, short for picture element, is one of the dots that make up an image on your computer. Since the CCD (charge-coupled device) array in a digital camera is a grid of sensors it can be described as a ratio of the height and width, for example 640 by 480. Multiplying these two numbers together gives you the total number of pixels. Divide that number by one million and you get the number of megapixels. In this case a 640 x 480 camera produces 307,200 pixels so it is a 0.3-megapixel camera.
This concept is also relevant to scanner and monitor descriptions. When a scanner is described as 600 dpi or dots-per-inch, this is referring to how many pixels can be recorded from an image. One square inch in a 600 dpi scan will be made up of 600 by 600 pixels. To get the total number of pixels in a scanned image you have to add in another factorsize. A 4-inch by 6-inch image scanned at 600 dpi will contain 8,640,000. The math works out as 4 x 600 (2400) multiplied with 6 x 600 (3600).
Monitors are described as a grid of the resolutions that they can display. A typical monitor will have a resolution of 1024 x 768 pixels. This is the equivalent of almost 0.8 megapixels. Pretty low if you were talking about a camera, but plenty for average computer use.
The number of pixels governs how well an image will look when displayed or printed at a given size. Your average computer screen shows an image at 72 dpi, but you will want at least 150 dpi for printing purposes. If you keep doing the math (sorry about the math) youll realize that the 640 x 480 camera is only good for decent printed images at about 3 x 4 in size. Thats smaller than the typical photo-mat 4 x 6 prints, so forget about even bigger enlargements unless you like that mosaic tile effect.
If you look at the chart in figure 1 you can see some of the standard camera sizes in megapixels and pixels and how big you can print the images. Some cameras will let you shoot images at lower than the maximum resolution of the camera. This is great if you will not need the full resolution, say for emailing the pictures. You dont usually want to email images that are too big to be seen on the recipients monitor. This will also allow you to store more images on your cameras memory card.
Camera manufacturers are usually eager to let you know how many megapixels their cameras will record. If the camera doesnt say, then it is probably pretty low. Cameras that are free with a subscription or that are offered at an incredibly low price are usually 0.3 megapixels or less. These are usually only suitable for emailing the pictures to your mom.
Next time you are out looking at the cornucopia of cameras at your local electronics outlet keep in mind the megapixels and how you intend to use the images. There are plenty to choose from and you should be able to find one thats right for your needs.