The term pixel is short for picture element. All digital pictures are composed of pixels, a single pixel being the smallest addressable element of such a picture. Pixels are rectangular (usually square). A computer picture, and indeed your entire computer screen, is therefore nothing more than a mosaic of tiny coloured rectangles arranged in rows and columns.
The number of pixels across and down an image or screen is called the resolution. The higher the resolution, the greater the detail that can be shown in the picture, but this also increases memory and disk space requirements. Storing large amounts of pixel data can take up so much space that sophisticated compression schemes have been developed to reduce the amount of space required. The most common compression method in general use is JPEG, an incredibly clever (and complex) method of reducing the data size of photographic images. PMIO uses JPEG compression internally to reduce the amount of space needed to store and manage thumbnails.
Each pixel in a true-colour image is represented inside the computer by three numbers, one for each of red, green and blue. By combining various combinations of red green and blue intensities, it is possible to create (almost) any desired colour on the screen. Each number has a range of 0 to 255. This gives 256 brightness levels for each of red, green and blue, making a total of 16.7 million possible colours. The real world contains an infinitely smooth range of colour shades, and a huge range of brightness, which is one reason why computer pictures never really look completely realistic.
PMIO works in true-colour, and expects your screen to be capable of at least a high-colour display. If you try to use it on a 256-colour display, the results will generally be unpleasant to look at. Most modern computers are capable of at least high-colour with a decent resolution and refresh rate.
