PIXEL

The term "pixel" is actually short for "Picture Element." These small little dots are what make up the images on computer displays, whether they are flat-screen (LCD) or tube (CRT) monitors. The screen is divided up into a matrix of thousands or even millions of pixels. On color monitors, each pixel is actually composed of three dots -- a red, a blue, and a green one.

Typically, you cannot see the individual pixels, because they are so small. This is a good thing, because most people prefer to look at smooth, clear images rather than blocky, "pixelated" ones. However, if you set your monitor to a low resolution, such as 640x480 and look closely at your screen, you will may be able to see the individual pixels. As you may have guessed, a resolution of 640x480 is comprised of a matrix of 640 by 480 pixels, or 307,200 in all. That's a lot of little dots.

In the picture below is an example of a close up of pixels on a LCD screen. As can be seen in the picture, we've zoomed into the "eye" part of the eagle to give a better understanding of how the display works. Each pixel is made up of a red, green, and blue (RGB) light that is increased or decreased in intensity to make up each of the colors you see on the screen.

Each pixel can only be one color at a time. However, since they are so small, pixels often blend together to form various shades and blends of colors. The number of colors each pixel can be is determined by the number of bits used to represent it. The number of bits used to represent each pixel determines how many colors or shades of gray can be displayed. For example, in 8-bit color mode, the color monitor uses 8 bits for each pixel, making it possible to display 2 to the 8th power (256) different colors or shades of gray.

 However, at 16, 24, and 32-bit color depths, the color blending is smooth and, unless you have some kind of extra-sensory vision capability, you should not see any graininess.

Mega Pixel
A megapixel (MP) is a million pixels; the term is used not only for the number of pixels in an image, but also to express the number of image sensor elements of digital cameras or the number of display elements of digital displays.

For example, a camera that makes a 2048×1536 pixel image (3,145,728 finished image pixels) typically uses a few extra rows and columns of sensor elements and is commonly said to have "3.2 megapixels" or "3.4 megapixels", depending on whether the number reported is the "effective" or the "total" pixel count

Large (3072 x 2304 pixels) -- 7 megapixels
Medium (2048 x 1536 pixels) -- about 3 megapixels
Small (640 x 480 pixels) -- .3 megapixels