The key purpose of a scanner is to analyze an image and process it. It is now an important part of the home office and used in many ways:
- Flatbed scanners or desktop scanners are the most versatile and frequently used scanners.
- Sheet-fed scanners generally move the documents as the scan head is immobile. It actually looks like a small portable printer.
- Handheld scanners rely on the user to move them rather than a motorized belt. It does not provide good image quality but can be useful for capturing text quickly.
- Drum scanners are useful to capture incredibly detailed images. They apply a technology called photomultiplier tube (PMT) where the document is mounted on a glass cylinder. There is a sensor that splits light bounced from the document into three beams at the center of the cylinder.
Anatomy of a Scanner
A typical flatbed scanner provides:
- Charge-coupled device (CCD) array
- Scan head
- Glass plate
- Stepper motor
- Stabilizer bar
- Power supply
- Interface port(s)
- Control circuitry
CCD array is the core component of a scanner. For image capturing in scanners, it is the most familiar technology. It consists of tiny light-sensitive diodes, which transfer photons (light) into electrons (electrical charge). The diodes are actually photosites and each photosite is sensitive to light.
The Scanning Process
The steps that a scanner goes through when it scans a document are given below:
- The document takes place on the glass plate and in the closed cover. The inside of the cover is flat white and some are black. A uniform background in the cover helps the scanner software to be useful as a reference point for determining the size of the document being scanned.
- A lamp, that illuminates the document, is either a cold cathode fluorescent lamp (CCFL) or a xenon lamp in newer scanners. But it may be a standard fluorescent lamp in older scanners.
- The entire mechanism including mirrors, lens, filter, and CCD array constructs the scan head. It moves slowly across the document by a belt that is connected to a stepper motor.
- An angled mirror reflects the image of the document to another mirror.
- The rear view mirror displays an image on the lens that focuses on the filter in the CCD list.
The filter and lens arrangement vary from scanner to scanner. Some scanners apply a three pass scanning method where each pass exploits a different color filter between the lens and CCD array. After completion of the three passes, the scanner software organizes the three filtered images into a single full-color image.
Contact Image Sensor (CIS) is an imaging array technology that has become popular in inexpensive flatbed scanners. The image sensor mechanism takes place very close to the glass plate where the document rests upon. While scanning the image, the LEDs combine to provide white light. The row of sensors then captures the illuminated image.
Unlike CCD scanners, CIS scanners are cheaper, lighter and thinner, but they can’t provide the same level of quality and resolution.
Resolution and Interpolation
Scanners diverge in resolution and sharpness and flatbed scanners contain a hardware resolution of at least 300×300 dots per inch (dpi). The number of sensors in a single row of the CCD or CIS array by the precision of the stepper motor determines the scanner’s dpi.
For instance, if the resolution is 300×300 dpi and the scanner is able to scan a letter-sized document, then the CCD will have 2,550 sensors organized in each horizontal row. And a single-pass scanner has three of these rows.
Sharpness is dependent on the quality of the optics and the brightness of the light source. A bright xenon lamp and high-quality lens will generate a much clearer and sharper image than a standard fluorescent lamp and basic lens.
The high resolutions are normally branded as software-enhanced, interpolated resolution or something similar. Interpolation is a procedure that the scanning software utilizes to increase the apparent resolution of an image. It can do this by producing extra pixels among the ones actually scanned by the CCD array. These additional pixels are an average of the adjoining pixels.
Bit depth or color depth means the number of colors that the scanner is capable of reproduce. To produce standard true color, each pixel requires 24 bits. Sometimes you can get bit depths of 30 or 36 bits. There are many judgments about whether there is a visible difference in quality between 24-, 30- and 36-bit scanners.
Document scanning is only one part of the process. For a scanned image to be valid, it must be transferred to your computer. You will find three common connections used by scanners:
- Parallel: The slowest transfer method is connecting through the parallel port.
- Small Computer System Interface (SCSI): SCSI obliges a special SCSI connection. Most SCSI scanners comprise a dedicated SCSI card to place in into your computer and connect the scanner.
- Universal Serial Bus (USB): USB scanners provide good speed, user-friendliness and affordability in a single package.
- FireWire: FireWire connections are faster than USB and SCSI and ideal for scanning high-resolution images.
You need software on your computer to call a driver that knows how to correspond with the scanner. There is a common language, TWAIN that most scanners can speak. The TWAIN driver operates as an interpreter between any application that maintains the TWAIN standard and the scanner. It does not need to recognize the specific details of the scanner.
Besides the driver, most scanners accompany other software. It also includes a scanning efficacy and some type of image editing application. Many of them provide OCR software. It allows you to scan in words from a document and translate them into computer-based text.
The scanner technology is excellent in a way that you can get exactly what you need. You can find a decent scanner with good software in a reasonable price.