Glossary

GLOSSARY BY CESCA HAIG

Pixel

Term pixel Is short for Picture Element, they are small dots that make up an image. A pixel is a physical point in a raster image, it is the smallest controllable element of a picture shown on screen. A screen can be made up of millions of pixels, each one is only one colour at a time. However, they do blend together and form various shades and blends of colours as they are so small. The number of colours a pixel can be is determined by the number of bits used to represent it.

Resolution.

Resolution refers to he sharpness of an image. It is most often used to describe monitors, printers and bi mapped graphic images. Bit map images are composed of pixels and the image resolution is simply the number of pixels per inch in the bitmap grid. Typical resolutions include – 256x256 – Very cheap cameras, resolution is so low that the quality of the image is almost always unacceptable. 65000 total pixels. 640x480 - Low end on most ‘real’ cameras. Ideal for emailing pictures or posting on websites. 1216x912 – Megapixel image size. 1,109,000 total pixels. Good for printing pictures. 1600x1200 – High resolution image. Almost 2 million pixels. 2240x1680 – Found on 4 megapixel cameras. 4064x2704 – Found on 11.1 megapixel cameras.

Screen Ratio

The aspect ratio of a screen or image describes the proportional relationship between its width and is height, it is commonly expressed as two numbers separated by a colon, as in 4:3 and 16:9. For an x:y aspect ration, no matter how big or small the image is, if the width is divided into x unit of equal length and the height will be measured by y units. An example of this is – if you have a group of images all with an aspect ratio of 16:9, one of these images is 16 inches wide and 9 inches 9 high. Another is 16 centimetres wide and 9 centimetres wide and another one is 8 yards and 4.5 yards high. 1:85:1 and 2:39:1 are the two most aspect ratios used today in films in movie theatres.

Frame Rate

Frame rate is the frequency at which an imaging device produces unique consecutive images called frames. Frame rate is often expressed in frames per second and is also expressed in progressive scan monitors as hertz. Frame rate ells you how many frames per second(fps) there are when recording or playing video. Video camera in Europe use 25fps and in the USA and Japan 29.97fps or 30fps is used. The human eye and its brain interface processes 10 to 12 separate images per second. Early films had a frame rate from 14 to 24 fps which was enough for a sense of motion, although it was perceived as jerky motion.

Video Format

Video format defines the way in which a video has been recorded and stored. Normally specifying- Codec/compressor, Frame rate, Frame size, Frame aspect ratio, Pixel aspect ratio, scanning method (interlaced or progressive) The common formats are DV, HDV and AVCD. The tape based formats like DV and HDV can be transferred to a computer for editing via Fire wire. File based formats such as AVCHD are already stored as files and they can be transferred to a computer for editing via USB or card reader. Any file based formats may need to be converted during or after transfer to be compatible with editing software.

Video formats

Compression

Codec is short for coder-decoder and describes the method in which video dadt is encoded into a file and decoded when the file is played back. Most videos are compressed during encoding, and so the terms codec and compressor are often used interchangeably. The process of converting from one codec to another is called transcoding. Codecs can be lossless, this means that they do not throw away any data, or lossy, which means that data is lost during encoding. Lossless codecs are higher quality than lossy codecs, but produce larger files.