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PCM: Abbreviation for Pulse Code Modulation. Sound is analog but computers are digital. For computer to deal with sound, the sound needs to be digitized. The most common technique for doing so is pulse code modulation. It's the native format used by WAV and AIFF files for representing sound. It's not well compressed, so sounds are often encoded further using a codec..
PCMCIA: Personal Computer Memory Card International Association. It is now known as PC card bus. PC cards are credit-card sized, hot-swappable devices that can perform virtually every PC function. Although originally visualized as memory cards, today PC cards hold hard drives, modems, network cards, sound cards, and SCSI host adapters. PC cards are available in three standard thicknesses. Type I is 3.3 mm thick and is rarely used today. Type II is 5 mm thick and is the most common PC card in use today. Type III is 10.5 mm thick and is used primarily for hard drives.
PC Card Reader: A peripheral that transfers images recorded on Compact Flash or Smart Media memory cards to PC.
Pixel: Short for picture element. A pixel is the smallest logical unit of visual information that can be used to build an image. Pixels are the little squares that can be seen when a graphic image is enlarged. The more pixels in an image, the better its resolution.
Pixel Map: A 3-dimensional array of bits represented as a 2-dimensional array of pixels, in which each pixel has a depth of a certain number of bits.
ppi: Pixels-per-inch. A measurement used to describe the size of the final printed image. An image that has a higher number of pixels-per-inch will show more detail than one which has fewer pixels-per-inch.
Pre-Flash: Some digital cameras fire two flashes, the first adjusts the white balance and the second exposes the picture. This is different from a red-eye reduction mode in which multiple weak flashes are fired to close down the subject's iris prior to the actual exposure.