- artefact
An unwelcome feature of an image, such as speckles or background noise, usually introduced by some scanner harware limitation, or use of image processing techniques.
- Auto Document Feeder (ADF)
An accessory that feeds pages into a scanner when required, enabling the unattended scanning of a large number of documents.
- CCD
Charge-coupled device, the electronic component most commonly used in scanners to convery light reflected from a document into digital information, which is then processed, sent to your PC, and displayed as the scanned image.
- channel
A term that's sometimes used to refer to one component of a colour image (red, green or blue for example). It's handy for when you want to manipulate channels serparately, perhaps increasing the brightness of the red channel to add more red to the image itself.
- contrast
The range between the darkest and lightest parts of an image. Part of the trick of improving scan quality is increasing contrast without losing detail in the brightest and darkest parts of the image.
- descreening
An option included in many scanner drivers that can help remove onpleasant dot patterns from newsprint or magazine images.
- dpi
Dots per inch. See resolution
- filters
Tools that allow you to apply effects to your images. These range from conventional options such as Sharpen, which are intended to improve the quality of an image, to more artistic special effects such as Emboss or Mosaic.
- gamma
The contrast around the midtone of an image. Adjust the gamma and you can alter the brightness of an image without drastically affecting shadows or highlights.
- greyscale
An image consisting of shades of grey, with no colour.
- halftone
A printing technique which uses patterns of dots to create the illusion of a continuous tone image.
- highlights
The lightest parts of an image.
- midtones
The area of an image between the highlights and the shadows.
- moire
The unpleasant dot pattern that can sometimes occur if you scan a magazine picture and didn't use the Descreening option.
- OCR
Optical Character Recognition is the process of analysing the shapes on a scanned image, recognising individual characters, and eventually converting them to editable text.
- pixel
Short for 'picture element', a pixel is the smallest dot that is used to make up an image.
- preview
A low quality, but fast scan, useful to get a qick idea of how a scanned image is going to look. With TWAIN software and many scanners, this is part of the set-up process to allow you to select a specific portion of a document.
- resolution
A measurement of the quality of an image, usually expressed in terms of the number of dots per inch (dpi) both horizontally and vertically that are used to make it up.
- shadows
The darkest parts of an image.
- TWAIN
Nothing to do with turgid, radio-friendly country rawk. TWAIN is the standard means by which a PC can send commands and retrieve data to an external device, most commonly a scanner or digital camera. Most advanced graphics programs support TWAIN, and so will work with your scanner immediately.
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