Scanners vary in resolution and sharpness . Most flatbed digital scanner have a true computer hardware resolution of at least 300x300 dots per inch ( dpi ) . The scanner’sdpiis determined by two factors :
Let ’s take a simple example : If a scanner’sresolutionis 300x300 dpi , and that scanner is capable of scan a letter - sized ( 8.5x11 - inch ) written document , then theCCDhas 2,550 sensors arrange in each horizontal rowing – 8.5 ( inches across ) x 300 ( x - instruction sampling rate ) = 2,550 . A single - pass scanner would have three of these rows for a total of 7,650 sensors . The high stepper motor in our good example is able to move in increments equal to 1/300ths of an in .
Sharpnessdepends mainly on thequality of the opticsused to make the lens system and thebrightness of thelightsource . A brightxenonlamp and high - calibre crystalline lens will make a much light and therefore acuate image than a standardfluorescentlamp and basic lens .
Of course , many scanners proclaim resolutions of 4,800x4,800 or even 9,600x9,600 . To accomplish a hardware resoluteness with an x - direction sampling rate of 9,600 would require a CCD raiment of 81,600 detector , which is almost unheard of . If you look at the specification , these high resolutions are commonly labeledsoftware - enhance , interpolated resolutionor something standardised . What does that mean ?
Interpolationis a summons that the scanning software apply to increase theperceived resolutionof an image . It does this by creatingextra pixelsin between the 1 actually scanned by the CCD array . These supererogatory pixels are aweighted averageof the neighboring pixels . For exercise , if the hardware resolution is 300x300 , and the falsify solution is 600x300 , then the software is adding a pixel between every two picture element scanned by a CCD sensor in each row .
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