What you need to know about pixels and image sizes

Digital pictures are made up of hundreds of thousands maybe even millions of tiny squares called picture elements or pixels. Each of these pixels is captured by a single photo site on the image sensor when you take a picture using a digital camera. Your computer and printer can use these tiny pixels to display and print photographs you have taken. In doing this, the computer divides the screen or printed page into a grid of pixels; this is very much like the way the image sensor is divided. It then uses the values stored in the digital photograph to specify the brightness and color of each pixel in this grid. Controlling, or addressing a grid of individual pixels in this way is called bit mapping and the digital images are called bit-maps.

Usually printer and scanner resolutions are specified by the number of dots per inch (dpi) that they print or scan. Pixels per inch generally refer to the image and display screen and dots per inch refers to the printer and printed image. On an average, monitors use 72 pixels per inch to display text and images, ink-jet printers range up to 1700 dots per inch and commercial typesetting machines range between 1,000 and 2,400 dots per inch.

Much like traditional cameras, light enters a digital camera through a lens controlled by a shutter. Digital cameras have one of three types of electronic shutters that control the exposure. The first is electronically shuttered sensors; they use the image sensor itself to set the exposure time. A timing circuit tells when to start and stop the exposure. Electromechanical shutters are mechanical devices that are controlled electronically. And then there are electro-optical shutters. Electro-optical shutters are electronically driven devices in front of the image sensor which change the optical path transmitted.

Resolution is commonly referred to as the quality of a digital image, whether printed or displayed on a screen. The quality of that image depends partly on the number of pixels used to create that image. The more pixels a digital camera offers the more detail the pictures taken will have. If you enlarge any digital image enough, the pixels will begin to show an effect this is called pixel-ization. The more pixels there are in an image, the more the image can be enlarged before the pixels begin to show an effect.

There are two kinds of resolution for cameras and scanners, optical and interpolated. The optical resolution of a camera or scanner is an absolute number, this is because of an image sensor's photo sites are physical devices that can be counted. In certain aspects to improve the resolution, the resolution can be increased using software. This process is called interpolated resolution. Interpolated resolution adds pixels to the image. To do this, software evaluates those pixels surrounding each new pixel to determine what its colors should be. Keep in mind interpolated resolution does not add any new information to the image, it just adds pixels and make the file larger.

The larger an image size in pixels is, the larger the image file needed to store it. Because of this, some cameras allow you to specify more than one size when you take a picture. You are likely to get better results with a larger image, but it isn't always needed.When the image is going to be displayed on the web or printed very small is when a larger image is not needed. Images that are going to be displayed on the web or printed very small will have smaller file sizes and you will be able to save more into the camera's memory.