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BTECLevel 3 Extended Diploma in Creative Media ProductionUnit 64: Motion Graphics and Compositing Video

Pixels


Pixels

In digital imaging, a pixel, or pel, (picture element) is a physical point in a raster image, or the smallest addressable element in a display device; so it is the smallest controllable element of a picture represented on the screen. The address of a pixel corresponds to its physical coordinates.

http://en.wikipedia.org/wiki/Pixel


Pixels

The term pixel is actually short for Picture Element. These small little dots are what make up the images on digital. The screen is divided up into a matrix of thousands or even millions of pixels.

Each pixel can only be one colour at a time. However, since they are so small, pixels often blend together to form various shades and blends of colours. The number of colours each pixel can be is determined by the number of bits used to represent it.

http://www.techterms.com/definition/pixel


Pixels and Colour

Colour Depth Colour "depth" is defined by the number of bits per pixel that can be displayed on a computer screen. Data is stored in bits. Each bit represents two colours because it has a value of 0 or 1. The more bits per pixel, the more colours can be displayed. Examples of colour depth are shown in the following table: Colour Depth1 bit colour4 bit colour8 bit colour24 bit colour

No. Of Colours21625616,777,216 or True Colour


Pixels and Colour

Determining Colour Depth - Since each bit represents 2 colours, it is easy to work out the number of colours for the various colour depths. The number of possible colours would be 2 to the power of the number of bits per pixel:

A colour depth of 4 bits would be 2 times itself 4 times:2 x 2 x 2 x 2 = 16 colours

A colour depth of 8 bits would be 2 times itself 8 times:2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 = 256 colours.

A colour depth of 24 bits would be 2 times itself 24 times:2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 = 16,777,216 colours


Converting Light - Cameras

Instead of film, a digital camera has a sensor that converts light into electrical charges.



Instead of film, a digital camera has a sensor that converts light into electrical charges. A digital camera takes light and focuses it via the lens onto this sensor made out of silicon. It is made up of a grid of tiny photosites that are sensitive to light. Each photosite is usually called a pixel, a contraction of "picture element". There are millions of these individual pixels in the sensor of a digital camera.



Each photosite or pixel on the sensor absorbs photons and releases electrons through the photoelectric effect. In the photoelectric effect, electrons are emitted from matter (metals and non-metallic solids, liquids or gases) as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light.



The image sensor employed by most digital cameras is a charge-coupled device (CCD), although some cameras use complementary metal oxide semiconductor (CMOS) technology instead. Both CCD and CMOS image sensors convert light into electrons. A simplified way to think about these sensors is to think of a 2-D array of thousands or millions of tiny solar cells. Once the sensor converts the light into electrons, it reads the value (accumulated charge) of each cell in the image. This electric charge is then transferred and converted to an analog voltage that is amplified and then sent to an Analog to Digital Converter where it is digitised (turned into a number).

pixel 200213

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