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15 Cards in this Set
- Front
- Back
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Bitmap
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A binary representation of an image, in whish each bit, is mapped to a point (pixel) on the output device, where the point with either be on(black) or off(white) or vice versa
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Byte
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The standard unit of binary hata storage in computer memory or disc files. A byte containing 8 bits can have any value btween zero and 255 (2^8)
One kilobyte (KB)=1024 bytes One Megabyte (MB)=1024 KB One Gigabyte (GB)=1024 MB |
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CCD - Charge coupled device
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A solid state image pick-up device composed of a rectangular matrix (area array) or single row(linear array) of light sensitive picture elements (pixels or photosites). Their operation is highly complex and only a brief explanation can be given here.
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CMOS sensors
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In digital cameras. Cheaper to manufacture. Each pixel contains both photodiode and tansistor to select, amplify, digitize and transfer the charge. This means that image processing can take place during capture rather than at a later point.
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Digitize
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Convert into digital form. Digitization us subdivided into processes of sampling the analogue signal at a moment in time, quantizing the sample (allocating it a numerical value) and coding the number in binary form. A digital image is made up of a grid of points. There is no continuous variation of colour of brightness. Each point on the grid has a specific value. Digital images are recorded as data and not as a signal.
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Down-Sample
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To reduce the resolution of an image
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Effective Pixels
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The actual number of pixels involved in the recording of an image. For example, the Nikon D100 DSLR camera has 3110 x 2030 pixels in total (6.31 million) but an effective 3026 X 2018 (6.11 million pixels) used in actual image production.
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FM Screen - Frequency modulated screening (Stochastic screening)
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An alternative to conventional screening that seperated an image into very fine, randomly placed dots as opposed to a grid of geometically alligned halftone cells. It is similar in concept to mezzotint, but whereas in a mezzotint the dots are meant to be large enough to be visual, with stochastic screening, the dots must be so small as to be invisible.
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Halftone
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The process of printing continuous tone photographic images by simulating the continuous tone with a series of dots of varying sizes.
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Image Resolution
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Digital images from digital cameras or scannera are composed of a square or rectangular grid of pixels. The resolution of digital images is quoted in the number of pixels per (linear) inch, or the total number of pixels in an image- usually millions of pixels (megapixels)
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Image Sensor
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Sensors for digital cameras. CCD and CMOS. Each type has several variants. Basically, an image sensor contains a grid of minute light sensitive pixels (photosites) which act like a photogenerative light meter, measuring the amount of light falling upon them, and generating an electrical current in proportion to its intensity.
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Jaggie
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Refers to displays of bitmapped images, where both curved and diagonal straight lines appear to be jagged as they are composed of square pixels. Also, when coloured objects fall across groups of pixels on the imaging sensor, colour aliasing may occur.
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JPEG
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Joint Photographic Experts Group: A widely used lossy compression routine for the storage of still photographic images. Users can specify the amount of compression used, when saving the image. ‘Progressive JPEG allows successive rendering of the image, whereby a low resolution of an image appears first, followed by increasingly higher resolution until the final version appears. It is widely used when placing images in Web pages on the Internet.
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Line Art
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Term given to diagrams consisting of black lines on a white background, or vice versa (binary)
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LPI - Lines per inch
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Lines per inch: The scale used by printers when specifying the halftone screen used in a printing process. Typical valued for different print media are:
Newspring 80-100 lpi Books 133 lpi High end Magazines 150-175 lpi Quality reports/brochures 200-300 lpi |
