What is a Pixel?

The image on the right shows a greatly magnified version of the pixels contained in the flower image on the left.

Digital images are made up of millions of little squares called pixels, which stands for picture elements. Each pixel is captured by a single spot on the image sensor in your digital camera or scanner, when you capture the photograph.

The computer sees these pixels just like the old Impressionist painters - the 'pointillists' did, when they painted with small dots of paint (see the magnified portion of the flower image above). The computer and printer then uses these pixels to display or print photographs - just like painting by the numbers.

Controlling a grid of individual pixels in this way is called bit mapping which is why digital images are called bitmaps.

Pixels & Image Quality

The quality of a digital image, whether printed or displayed on a screen, depends in part on the number of pixels used to create the image - the resolution. The maximum number that you can capture depends on how complex the image sensor is, that is used to capture the image.

Some cameras add additional pixels to artificially inflate the size of the image. You can do the same thing in an image-editing program, but In most cases this only makes the image larger without making it better and often even degrades the image quality.

The DPI Dilemma

Using Digital Images for Greatest Effect

Know what you want before you go out and get it!

Capture the image at the correct resolution at which it is to be used. A 300 dpi (dots per inch) image, while perfect for printing, is overkill for a website or onscreen presentation which only requires a resolution of 72 dpi (96 dpi for Macs).

The dimensions of the image are also important - an image which is slightly larger than necessary is better than one which is too small and would need to be stretched to fit, since stretching an image would degrade quality.