kopia lustrzana https://gitlab.com/sane-project/website
138 wiersze
5.2 KiB
HTML
138 wiersze
5.2 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<html>
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<head>
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<title>SANE - How Scanners Work</title>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<meta name="author" content="Henning Meier-Geinitz">
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<meta name="keywords" content="sane, scanner, scanning, work, principle, calibration">
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<meta name="description" content="Short description on how scanners work">
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<link rel="icon" href="favicon.ico" type="image/x-icon">
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<link rel="shortcut icon" href="favicon.ico" type="image/x-icon">
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</head>
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<body bgcolor="#FFFFFF" text="#000000">
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<center>
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<a href="./"><img src="images/sane.png"
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alt="SANE" height="117" width="346" border="0"></a>
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</center>
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<center>
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<h1>SANE - How Scanners Work</h1>
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</center>
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<hr>
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<p>
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The idea of this document is to explain some basic principles of scanning
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hardware and software. It's not related to any specific scanners nor to
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any specific scanning software.
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</p>
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<p>
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At the moment it's a template only. Feel free to add what you are
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interested in.
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</p>
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<h2>Hardware (or: what is inside the scanner?)</h2>
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<h3>General Scanner Types</h3>
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<h4>Flatbed Scanners</h4>
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<p>
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Flatbed scanners provide a glass pane where the physical image is placed
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face down. The image is scanned by a movable sensor below the glass while
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the original does not move. The size of the physical image is limited by
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the glass pane.
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</p>
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<h4>Sheetfed scanners</h4>
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<p>
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This type of scanner has a fixed sensor whereas the physical image (piece
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of paper) is moved during the scan. Most scanners of this type have an
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automatic document feeder which can carry more than one piece of paper.
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</p>
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<h4>Film/Slide/Negative Scanners</h4>
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<p>
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These scanners are used to scan transparent material like negative films
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or slides.
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</p>
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<h4>Handheld scanner</h4>
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<p>
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Handheld scanners are moved manually on the physical image. Because of
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practical reasons the image width is limited but the length is
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theoretically endless. While handheld scanners were qwuite popular about
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10 years ago they are seldomly used nowadays.
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</p>
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<h3>Accessories</h3>
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<p>
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For most scanners one or more of the following accessories exist, either
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optionally or already included.
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</p>
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<h4>Transparency Adapter (TA)</h4>
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<p>
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A transparency adpater is used to scan transparent images (negative
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films, slides) on a flatbed scanner. A fixed or movable lamp is mounted on
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top of the scanner. Therefore the physical image is between the light and
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the sensor. Most scanners turn off the internal lamp when using the
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TA. Often the scan area is smaller then the full flabed area and the
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images are mounted in special frames.
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</p>
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<h4>Automatic Document Feeder (ADF)</h4>
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<p>
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While sheetfed scanners always provide automatic document feeders, ADFs
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are also available for some flatbed scanners. Usually a stack of papers
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can be placed on the scanners. With an automatic document feeder, many
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pieces of paper can be scanned in one batch without manual
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intervention. The pages are either moved through the scanner at constant
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speed and fixed sensor or scanned by a moving sensor after beeing placed
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on the fladbed automatically.
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</p>
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<h3>Image Sensor types</h3>
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<p>
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The image sensor is that part of the scanner, which translates the physical image it
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"sees" to analogue electrical signals. The physical image which is to be scanned is
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illuminated by a lamp (or LEDs). For reflective scanning (e.g. papers),
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the lamp is usually part of the sensor mounting plate or slider. For
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negative or positive scanning, the negative film or slide is located
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between the lamp and the sensor. While several types of image sensors are
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used, these are the main categories:
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</p>
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<h4>CCD</h4>
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<p>
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A charged-coupled device (CCD) sensor is an integrated circuit based on a
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one-dimensional array of capacitors. The image is projected on the CCD by
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a lens and/or mirror system from the physical image. There is one sensor
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line with included filter for each color (RGB, sometimes infrared). Older
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three-pass scanners had only one sensor line and a movable filter, which
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required three passes two scann in a color image. Usually cold cathode
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fluorescent lamps (CCFL) are used to illuminate the physical image.
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</p>
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<h4>CIS</h4>
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<h3>Analog frontend (AFE)</h3>
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<h3>Interface chips</h3>
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<h3>Stepper motor and driver</h3>
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<h3>Image buffer (RAM)</h3>
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<h3>Calibration area</h3>
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<h2>Software (or: how does this thing work?)</h2>
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<p>
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Keep in mind that some of the steps mentioned here can be done by the
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scanner itsself (its firmware) without engagement of the driver.
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</p>
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<h3>Calibration</h3>
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<h3>Line-distance correction</h3>
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<h3>Interpolation</h3>
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<h3>Gamma correction</h3>
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<hr>
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<p>
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<a href="./">SANE homepage</a><br>
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<a href="imprint.html">Contact</a>
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</p>
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</body>
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</html>
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