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Technical Advisory Service for Images Advice Paper Scanners Putting you in the picture – digital images in education © TASI · Last reviewed - July 2002 ? All scanners have the following components in common: an optical system, a light sensor, an interface and driver software. Exactly what form these components take and how they are arranged is what differentiates the scanner types. The quality of the scan obtainable is primarily dependent on the quality of the optics and the light detector, but the productivity is mainly reliant on the interface and driver Scanners are the most common digital capture device, their purpose being to convert light (which we see when we look at something) into ‘0’s and ‘1’s that we can store and use in a computer. Or put more simply, scanners convert analogue images into digital image files. The large fall in cost of scanners over the last decade means that they are no longer the specialist item they once were. However the range of prices and specifications of the scanners on the market can easily confuse the potential buyer. The different types of scanner (flatbed, film, drum and others) only adds to the confusion. Before examining the different types of scanner, lets take a look at the underlying technology and consider some of the issues that need to be considered when choosing and using them. Resolution Resolution is probably the specification that causes most confusion for newcomers to scanning. It is simply a measure of the ability to capture detail within the original work. Scanner manufacturers normally specify two figures for this parameter: ‘optical’ and ‘interpolated’ – however only the ‘optical’ figure gives a true indication of a scanner’s capabilities. For scanners that use Charge Coupled Devices (CCD) as the sensor, the optical resolution is limited by the number of elements (pixels) in the detector array and how the array is moved relative to the image. Resolution is specified by the number of separate and distinct samples that the sensor can make in every inch and therefore measured in samples per inch (spi), although often the more generic ‘dpi’ (dots per inch) is given by manufacturers. The figure given for ‘interpolated’ resolution is a result of the scanner software 'guessing' the values between pixels and presenting these intermediate values as 'real' values. This process gives no extra image information but merely smoothes the visual information and increases the size of the file. There are very few times when this process is in any way useful and when it is; it can be better undertaken within image processing software. So, remember that when assessing a scanner’s resolution, it is only the ‘optical’ figure that should be taken into account.
Object Description
Title | Technical Advisory Service for Images |
Subject |
Digital images Advice Computers |
Description | Advice Paper on Scanners |
Creator | Technical Advisory Service for Images |
Date | 2002-07 |
Type | compound object pdf with text |
Format |
Description
Title | Page 1 |
Transcript | Technical Advisory Service for Images Advice Paper Scanners Putting you in the picture – digital images in education © TASI · Last reviewed - July 2002 ? All scanners have the following components in common: an optical system, a light sensor, an interface and driver software. Exactly what form these components take and how they are arranged is what differentiates the scanner types. The quality of the scan obtainable is primarily dependent on the quality of the optics and the light detector, but the productivity is mainly reliant on the interface and driver Scanners are the most common digital capture device, their purpose being to convert light (which we see when we look at something) into ‘0’s and ‘1’s that we can store and use in a computer. Or put more simply, scanners convert analogue images into digital image files. The large fall in cost of scanners over the last decade means that they are no longer the specialist item they once were. However the range of prices and specifications of the scanners on the market can easily confuse the potential buyer. The different types of scanner (flatbed, film, drum and others) only adds to the confusion. Before examining the different types of scanner, lets take a look at the underlying technology and consider some of the issues that need to be considered when choosing and using them. Resolution Resolution is probably the specification that causes most confusion for newcomers to scanning. It is simply a measure of the ability to capture detail within the original work. Scanner manufacturers normally specify two figures for this parameter: ‘optical’ and ‘interpolated’ – however only the ‘optical’ figure gives a true indication of a scanner’s capabilities. For scanners that use Charge Coupled Devices (CCD) as the sensor, the optical resolution is limited by the number of elements (pixels) in the detector array and how the array is moved relative to the image. Resolution is specified by the number of separate and distinct samples that the sensor can make in every inch and therefore measured in samples per inch (spi), although often the more generic ‘dpi’ (dots per inch) is given by manufacturers. The figure given for ‘interpolated’ resolution is a result of the scanner software 'guessing' the values between pixels and presenting these intermediate values as 'real' values. This process gives no extra image information but merely smoothes the visual information and increases the size of the file. There are very few times when this process is in any way useful and when it is; it can be better undertaken within image processing software. So, remember that when assessing a scanner’s resolution, it is only the ‘optical’ figure that should be taken into account. |
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