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A scanner is an input device that:
- scans images
- prints text
- prints handwriting
- prints an object and converts it to digital images
Kinds of Scanners
- Drum scanners have rotating drums with a one-photo detector for a standard speed of 60 or 120 rpm. Using a telephone voice line to receptor, they can send linear analog AM signals. It prints the proportional intensity on special paper synchronously. This was used from the 1920s to the 1990s.
Color photos were sent as three separated and repeated RGB filtered images. This was only used occasionally because of the transmission cost.
- Desktop scanners or flatbed scanners found in offices are common examples of scanners. Documents are placed on the glass window for scanning.
- Handheld scanners are devices moved by hand. It evolves from text scanning to 3D scanners which are used for:
• industrial design
• reverse engineering
• test measurement
• orthotics
• gaming and more
These mechanically-driven scanners are used for large-format documents. Flatbed designs are not practical.
What these scanners use:
1. Modern scanners use image sensors such as:
• Charge-coupled device (CCD) or
• Contact Image Sensor (CIS)
2. Older drum scanners use a photomultiplier tube as its image sensor.
3. Rotary Scanner uses a CCD selection instead of a photomultiplier. Rotary Scanner is used for express document scanning. This is another type of drum scanner.
4. Planetary Scanner takes photographs of books and documents.
5. 3D Scanners are used for producing three-dimensional models of objects.
Other category of scanners:
Digital Camera Scanners
This is a reprographic camera. It becomes an attractive alternative to ordinary scanners. The disadvantages of this scanner are:
• distortion
• reflection
• shadows
• low contrast
Some of the advantages are:
• speed
• portability
• gentle digitizing of thick documents without damaging the book spine
The new scanning evolution combines 3D scanners with digital cameras. This is to make:
- full color
- photo realistic 3D model objects
Flatbed Scanners possess a glass pane with a bright light. These bright lights illuminate the pane and move optical selection which may be CCD or CIS.
These lights are usually:
• xenon or
• cold cathode fluorescent
Color scanners usually have three rows of sensors with:
• red
• green and
• blue filters
The images are scanned by placing images face down on the glass. An opaque cover is lowered over it so as to cover ambient light. The sensor selection will move over the pane in order to read the entire copy. Due to the reflecting light, the image becomes visible to the charge-coupled device. See-through images do not work this way. It needs special accessories in order to light them up from the upper side.
Scanning is only a part of the process. In order to make the scanned object useful, it must be transferred to an application running on the computer.
There are two basic issues with this:
1. the physical connection of the scanner to the computer and
2. the information retrieval of the application from the scanner
The Physical Connection of the Scanner to the Computer
The amount of data gathered by a scanner can be very large.
For example: A 600 DPI 9” x 11” uncompressed 24-bit image. It consumes about 100 megabytes. With this, uncompressed data is transferred and stored on the computer. The latest scanners can gather this volume of data in a matter of seconds. It makes a desirably fast connection.
The Four Connections used by Scanner
1. Parallel
2. Small Computer System Interface (SCSI)
3. Universal Serial Bus (USB)
4. Fire Wire
Application Programming Interface
An application must be able to communicate with scanners such as Adobe Photoshop. There are different scanners and each scanner has different protocols. To simplify application for programming, Application Programming Interfaces were made. Hence, API gives a uniform interface to the scanner. The application does not require knowing the specific details of the scanner so as to access it directly.
In reality, there are problems with an application communicating with scanners. Maybe the application or the manufacturer of the scanner has made a mistake in their implementation of API.
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