In most computer scanners, the electron beam is scanned back and forth across the sensor. When the beam strikes a positive charge, it will be reflected in the opposite direction. Once this occurs, the pixel is declared to be on. If there is no positive charge, the electron beam will pass through with no effect (and thus, determined to be off). The circuitry then subtracts information from each row as it scans down creating an image made up of only pixels that are on.
Table of Contents
Scanner converts the document image into a digital file
It sounds like you’re asking how they convert the image into a digital file.I think the first thing to understand is that the image is being captured as a series of lines. The “scanner” sweeps across the document, typically using reflected light to capture the information.
This is turned into a digital representation by capturing the intensity of each pixel in each row as it moves across. This is turned into a series of bits (0’s and 1’s) describing each pixel, giving the “bitmap” representation of the document.
The basic structure of the scanner is that it has a high-intensity light source, with a mirror and a lens
The basic structure of the scanner is that it has a high-intensity light source, with a mirror and a lens. The light source and mirror are fixed to the scanner housing, but the lens is on a carriage that is moved back and forth by precision stepper motors.As the lens moves along, it scans an image line at a time onto the flatbed surface of the scanner.
This carriage is moved across the width of the scanner, and then back again. As it does this, it moves in synch with the page being scanned, so that each line is scanned as it moves under the lens.Once each line has been scanned, the page moves one increment forward (or backward) so that another line can be scanned. This continues until the entire page has been scanned.If you look carefully at many scanners while they are scanning, you can see this happening right before your eyes.
The light source in scanners
- The light source in scanners is typically made up of fluorescent lamps and glass optics. The lamps are generally designed to emit a line of light and can be moved by a stepping motor to accumulate the data needed.
- The scanner unit contains a lens system: the lens focuses the light reflected from the document onto the sensor, where the image is digitized.
- Laser scanners use either a rotating polygonal mirror or a rotating multifaceted mirror to direct light from an external source onto a horizontal flat-bed scanner.
- A flat-bed scanner has its own built-in light source, and it moves the document face down under a stationary glass window.Some scanners use arrays of tiny charged coupled devices (CCDs) instead of single sensors. These CCDs are very fast and highly sensitive, so they can work in low light conditions without using flash illumination.
The image sensor in scanners
The image sensor in scanners is CCD or Charge Coupled Device. It is a semiconductor device like that used in a digital camera. The pixels of the CCD array are exposed to light and the charge produced by it is amplified and digitized to produce an image, which can be stored in standard formats.The CCD requires a power source to operate, but because the output from a scanner can be quite large, it would be undesirable for the entire surface of the scanner to be powered.
So instead, only one portion of the CCD has power at any given time, and it scans across the page so that each area of the scanner produces its own electronic impulse. That is why when using a flatbed scanner, you have to wait for the scan bar to move across before you can lift up your document.One advantage of a CCD over traditional photographic film is that it does not require an emulsion layer. This means that the sensor in scanners can be much more sensitive to light than film.
But there are also CIS or Contact Image Sensor can be used as an alternative to CCD
I believe you are talking about an image scanner, the type that scans a picture of a document and produces an image file. The image is usually composed of pixels (colored squares). A CCD or Charge Coupled Device is a set of light sensitive elements that will capture the reflected light from the object being scanned.
But there are also CIS or Contact Image Sensor that can be used as an alternative to CCD.
Conclusion
All in all, the basic principle by which scanners convert images to digital form is the same. Whether you want to purchase a flatbed or an office scanner, it’s best to consider your scanning needs and habits before making your decision.
We hope that this guide has helped you learn more about how computer scanners work and about some of the decisions you’ll have to make when purchasing a new one.