See also: Px

The pixel ( px in summary), is the basic unit of a Digital image. Its name comes from the English phrase pict RUE el ement , which means, “element of image” or “not elementary”. Certain documents (of origin IBM) also speak about pel .

It is the addressable minimal point by the video controller. It is for example the unit used to specify the definitions of posting (width × height):

• the definition of VGA (video graphics array) is of 640×480, that is to say: 307200 points;
• the definition of the Super-VGA or S-VGA (super video graphics array) is of 800×600, that is to say: 480000 pixels;
• the definition of XGA (eXtended graphics array) is of: 1024×768, is: 786432 pixels;
• the definition of SXGA (super extended graphics array) is of: 1280×: 1024, are: 1310720 pixels.
• the definition of UXGA (ultra extended graphics array) is of: 1600×: 1200, are: 1920000 pixels.

With each pixel a Couleur, usually broken up into three primary components is associated (see the article Rouge blue green ).

On a traditional cathode screen, each pixel is reconstituted by a triad of components électrolumininescents, returning tons red, green and blue once bombarded by the Electron gun of the cathode tube.

Dimension of a point

The size of a point - height and width are normally identical - is the relationship between the height of posting and the number of points in height, or between the width of posting and the number of points in width. By supposing that the diagonal of the image is the diagonal of the screen (in fact, it is slightly lower), one can calculate the dimension of the point.

Usually, one indicates the size of the screen by giving the length of the diagonal, in Centimètre S or possibly in inches. Here some examples of values

For the Television, there are typically three analogical standards: the STAKE, the SECAM and NTSC. The STAKE and the SECAM have both a vertical resolution of 625 lines, and the NTSC 525 lines. The following sizes of point are thus obtained (format 4/3):

Cut memory of a point

For data processing, a point is coded on several Bit S (see the data-processing article Codage of the colors ). The place memory occupied by a point depends on the “depth”, i.e. number of displayable colors:

• Black and white: a bit (1/8e of Byte);
• 16 colors (standard VGA): 4 bits;
• 256 colors: 1 byte;
• : 65536 colors (“thousands of colors”): 2 bytes (16 bits);
• : 16777216 colors (“16 million colors”, “true colors” ): 3 bytes (24 bits).

The place real memory used can be more important. For example, in mode 16 million colors, the point occupies 32 bits (4 bytes), the additional byte unutilised or being used by OpenGL.

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