Whether shooting with a digital camera, scanning existing photos to digital format, or printing images from a computer (digital) file, there seems to be a lot of misunderstanding about digital imaging. If you free yourself from the mystery and misinformation that surrounds this fabulous development of technology, you will discover the freedom to enjoy taking pictures more than you ever did with a film camera.

First of all, you need to understand that any computer file is "digital". All computer files are binary. That means every letter, word, and file in your computer is made up entirely of zeros and ones. (That's right, just two "digits") Even if you still think the computer is magic, you don't allow yourself to be confused worrying about that, so don't make mountains out of pixels!

Most peoples' confusion arises when they try to equate pixels per inch (ppi) with the printer's dots per inch (dpi). The two are loosely related, but they are not equal.

Next, let us clarify the terminology: "Pixel" is a computerese term made by combining two words…"picture" and "element." A pixel is the smallest element (or part) of a picture as it displays on your screen. Think of it as a map divided into sections, with numbers across the top and letters of the alphabet down the side, to help us find specific locations. A digital display is nothing more than a grid (map) of squares (pixels), and each pixel includes information telling the monitor what color should be displayed at that location.

PPI (pixels per inch) correctly used, refers to monitor resolution. A digital image is composed of bits of data gleaned by sampling the original image so many times per inch. The monitor screen is set to display so many pixels horizontally and so many vertically (for example: 800 X 600). The computer converts the stored image file to a format the monitor can display. The PPI is the display resolution not the image resolution. (Adobe Photoshop uses PPI and Corel Photo-Paint uses DPI for image resolution so it's no wonder everyone is confused.)

SPI (samples per inch) refers to scanner and/or image resolution. All computer images are digital, whether created by digital camera, or by scanner. The digital image is created by sampling portions of the original. The more samples it takes per inch, the closer it will be to the original un-digitized image. The greater number of samples per inch, or SPI, the higher the resolution.

DPI (dots per inch) is a measure of printer resolution. It properly refers to the dots of ink or toner used by a printer, to print an image. In general, the more dots per inch, the better and sharper the image.

*It is important to remember that many of the tips, tutorials, software, and even instructions that come with cameras and scanners use SPI/PPI/DPI interchangeably. Look at the terms in context to help you decide whether it means samples, pixels, or dots.

To fully understand all these terms we need to know more than the proper definitions. We need to know how this translates to real world usage. Next month I'll explain each term more fully and provide examples of how the terms relate to each other, to onscreen display and to printing.

"I'll byte back."
The Pixelator