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  • 1. Glossary.PixelsIn digital imaging a pixel is a physical point in a raster image, or the smallest addressable element ina display device. It is the smallest controllable element of a picture represented on the screen. Theaddress of a pixel corresponds to its physical coordinates.The term pixel is short for picture element. The small little dots are what make up the images ondigital. The screen is divided up into thousands, even millions of pixels.Each of the pixels can only be one colour at a time, however because they are so small they usuallyblend together to make different shades of colours. The number of colours each pixel can be isdetermined by the number of bits used to represent it.Colour and depth of pixelsColour depth depends on the number of bits per pixel that can be displayed on a computer screen.The data is stored in bits. Each bit represents two colours because it has a value of 1 or 0. The morebits per pixel, the more colour can be displayed. Examples of colour depth are shown below:Colour depth No. of colours1 bit colour 24 bit colour 168 bit colour 25624 bit colour16,777,216 or True ColourInstead of a film, a digital camera has a sensor that converts lights into electrical charges. A digitalcamera takes light and focuses it via the lens onto this sensor made of silicon. It is made up of a gridof tiny photosites that are sensitive to light. Each photosite is usually called a pixel, a contraction ofpicture element.ResolutionBitmap images are composed of pixels. Image resolution is basically the number of pixels per inch(PPI) in the bitmap grid. There are two aspects to every bitmap image – its size (width and height)and resolution. These two factors determine the total number of pixels in an image.The usual resolutions include:256x256 – found on cheap cameras, this is 65,000 total pixels640x480 – this is considered the “low” end on real cameras. This resolution is ideal for emails andposting pictures on a website.1216x912 – this is a megapixel image size. Good for printing pictures.
  • 2. 1600x1200 – with almost 2 million pixels this is considered high resolution. You can print a 4x5 inchprint taken at this resolution with the same quality you’d get at a photo lab.2240x1680 – found on 4 megapixel cameras – the current standard; this allows larger printed imageswith good quality for up to 16x20 inches.4064x2704 – a top of the line digital camera with 11.1 megapixels takes pictures at this resolution.At this setting you can create 13.5x9 inch prints with no loss of quality.Resolution has a huge impact on an image. For example, in Photoshop we usually have to adjust theresolution levels so the image is the best quality possible. If the picture has low resolution, it’ssometimes very clear to see and noticeable. If you don’t adjust the resolution or take a poor qualityimage then the pixels will be really visible.Screen ratiosThe aspect ratio of a screen or image describes the proportional relationship between its width andheight. It is commonly expressed as two numbers separated by a colon. For an x:y ratio, no matterhow big or small the image is, if the width is divided into x units of equal length and the height ismeasured using this same length unit , the height will be measured to be y units.In still camera photography, the most common aspect ratios are 4:3, 3:2, and more recently found incameras 16:9.This is important as many DSLR’s are being used to shoot video due to the quality oftheir internal sensors and superior lenses.Frame rateFrame rate, also known as frame frequency is the frequency (rate) at which an imaging deviceproduces unique consecutive images called frames. This term also applies to film and video cameras,computer graphics, and motion capture systems. Frame rate is usually shortened to FPS (frames persecond)The human and its eye interface, our visual system can process 10 to 12 separate images per second.Video Formats.A video formats defines the way in which video is recorded and stored. It normally specifies: Codeccompressor, frame rate, frame size, frame aspect ratio, pixel aspect ratio, and scanning method.Common formats are DV, HDV and AVCHD. Tape based formats like DV and HDV can be transferredto a computer for editing via FireWire whereas file based formats such as AVCHD are already storedas files and can be transferred to a computer for editing via a USB or a card reader.CompressionCodec is short for coder decoder and describes the method in which video data is encoded into a fileand decoded when the file is played back. Most of the video is compressed during encoding so theterms codec and compressor are often used interchangeably.