Digital Image Tutorial

What Are Digital Images?

Digital images are images in digital format--a collection of visual information stored in computer-readable format. Digital images are drawn on the computer screen using pixels. The information for each pixel in the image is stored in a computer file on the hard disk or flash memory of your camera. For the purposes of this tutorial, digital Images are any picture that has been converted so that it can be viewed on a computer.

Sources of Digital Images

• Digital Cameras
• Scanners
• Microsocopes
• Telecopes

What are PIXELS?

A pixel contains color information about one specific spot in the image. Pixels are the smallest piece of information in a digital image file. Strictly speaking, a pixel has no height, width or depth measurement. A pixel's size depends upon the device displaying the pixel. Digital images do have a setting called resolution which (in theory) indicates the number of pixels per inch of the image, but this will vary depending upon where the image is being displayed or printed.

Resolution

Resolution is a measurement that defines the number of "pixels per inch" in the digital image. This number can be changed by the user using software such as Photoshop. Whenever the image is to be displayed on a computer monitor, this setting becomes irrelevant. All computer monitors have small cells in the display surface that are of fixed size. One pixel normally equals one of these cells. Thus, the 'pixels per inch' is somewhat limted to what the computer monitor can display. If your monitor's screen is 16 inches wide and it has 1600 little cells from left to right across the display, the monitor could be said to display images at a resolution of 100 pixels per inch.

However, graphics software (Photoshop, Paint Shop Pro and most photo editing software) can attempt to either 'dither down' higher resolution images to fit on lower resolution screens or they can stretch the pixels over more than one cell on the monitor's screen.

Resolution settings are used primarilly when you try to print your image. Computer monitors support anything between 72 and 93 pixels per inch. This varies by monitor. Printing systems can change the size of their dots to get more or less dots per inch. Generally, printing 1 pixel per dot per inch is the default setting in most printing systems. Some printing systems can vary the size of their dots.

Try to remember that when printing an image, any resolution setting beyond 100 pixels per inch will look acceptably sharp to the human eye when held 10 inches or more from your face--provided your image was sharp to start with..

Dimensions

A digital image's dimensions are equal to the number of pixels in the horizontal and vertical dimensions of the image. Many people use the term 'resolution' for the dimension of their image, but resolution more properly refers to the number of pixels per inch.

There are several 'standard' dimension settings for computer displays:

• 640x480
• 800x600
• 1024x768
• 1152x864
• 1280x1024
• 1600x1200
• 1800x1440