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A tag or piece of code that collects and transmits data from a website to a back-end server or data base.

Pixel (Wikipedia)
This example shows an image with a portion greatly enlarged, in which the individual pixels are rendered as small squares and can easily be seen.
A photograph of sub-pixel display elements on a laptop's LCD screen

In digital imaging, a pixel, pel, or picture element is a physical point in a raster image, or the smallest addressable element in an all points addressable display device; so it is the smallest controllable element of a picture represented on the screen.

Each pixel is a sample of an original image; more samples typically provide more accurate representations of the original. The intensity of each pixel is variable. In color imaging systems, a color is typically represented by three or four component intensities such as red, green, and blue, or cyan, magenta, yellow, and black.

In some contexts (such as descriptions of camera sensors), pixel refers to a single scalar element of a multi-component representation (called a photosite in the camera sensor context, although sensel is sometimes used), while in yet other contexts it may refer to the set of component intensities for a spatial position.

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