What Does a Scanner See How it Works

What does a scanner see? Admit it; we have always been curious about what happens after we close the lid of a scanner, or after we feed a document into it. How can it capture the same exact document? Is it like taking a picture? Is there magic involved?

All these questions and more will be answered in this article. What is fascinating to note, is that a quick Google search of the phrase “what does a scanner see” will lead you to a poetic quote by Phillip K. Dick.  Frankly enough, this quote actually refers to the things we should know, to figure out how a scanner works.

Parts of the quote include, “… I mean, really see? Into the head? Down into the heart? Does a passive infrared scanner like they used to use or a cube-type holo-scanner like they use these days, the latest thing, see into me – into us – clearly or darkly?”

Getting past the very romanticized metaphors, you will see that it enumerated some parts of the scanner. This is exactly where we should start since before we can determine how a scanner works, we first should also know its core. Read on for more information.

Parts of a Scanner

Scanners come in different forms, shapes, and sizes. However, more often than not, they have the same core components, and these are:

Glass plate

This is where you will put the document that you want to scan. There are also plates that are made of thin transparent plastic, but most definitely, a glass plate will give the clearest view of your document.

Lid cover

This is the part that presses down on your document. Another function of the lid is to provide complete darkness onto the area of the glass plate, so you will have a clear copy.

Stabilizer bar

Depending on the type of scanner, you will usually see this under the cover or below the glass plate. This bar holds the scan head, to make sure that it will scan straight.

Lamp or lights

Usually, LEDs or fluorescent lights are used. The light in a way is the only sense of sight of the scanner. When you have a burnt out light, your scan will be unclear.

Scan head

This is the thing that rolls over, or passes through your document, for the scanning process to begin.


These are important as the process includes a lot of reflection of the image that is being scanned.


The reflections are captured through the use of the lens.


The captured images travel through these filter for further data processing.

Charge-Coupled Device (CCD) array

This is where the conversion of the captured “light image” is turned into electrons. Once it is turned into electrons, it can now be read by the software. The actual scan culminates in this part of the scanner because it is composed of light-sensitive diodes that makes this much-needed conversion possible.

Power supply

Most smaller scanners do not need a power supply, but the big ones need it to avoid short circuits.

Interface ports

These are ports to attach other accessories. These ports are also used to attach your scanner to a computer or laptop.

What Does a Scanner See: The Scanning Process

A scanner sees nothing—it sees a black space. But when it starts to do its thing, it does not really see your document, but it sees light patterns. Here is the complete process:

1.  You put your document on the glass plate, and you close the lid. Closing the lid is important because it is used as a reference point on how big or how small your document is.

2.  A lamp will now illuminate your document, once you press “start.”

3.  The scan head will now slowly move towards your document to make a “pass.” A successful pass means that the scan head was able to complete a single scan. In other types of scanners, the scan head rolls.

4.  The scan head will go over a document again if it was not able to complete a successful pass. Also, this head is attached to the stabilizer bar to make sure there will be no wobbles.

5.  Once a successful pass is done, the image of a document is reflected by an angled mirror to an opposite mirror. Usually, scanners only use two mirrors, but there are others that use three. The mirrors are curved slightly so it will be easier to reflect an image to a small space.

6.  The second or third mirror will then reflect the image to the lens.

7.  The lens and the filter will work together to focus the image for processing in the CCD array.

8.  The CCD array now converts the image into data that can read by the software of your computer.

9.  The image is now shown on your computer.

10.  You can choose to print out the image or keep a soft copy.

When you read through the process, it is an arduous one. However, in today’s technology, this process only takes about five seconds to complete. So there you have it, a scanner does not really see your document, it only sees the light, and the image is focused through a series of reflections until finally this image is converted into computer data.

Other Facts About Scanners

Here are some pretty surprising facts about using a scanner:

  • It is better to scan film than prints. This is the case because as we have discussed earlier, the scanner sees only light. So when you scan a film, it is easier to process, since the colors of a negative are still underdeveloped.
  • It is not about the type of scanner, but the type of sensor. This boils down to preference, but it has something to do with capturing the right tones of colors and maintaining the proper resolutions.


Figuring out what a scanner sees and how it works is really interesting. Not only it is amazing to know that all of our scans are made possible by simple reflections, but it also shows how far we have come in terms of technology.

At the same time, being equipped with this knowledge will surely help you when your scanner breaks down. You might just surprise yourself, that you have already fixed it on your own.

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