Scanners 101

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computerhakk

computerhakk

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Scanners 101

Table of Contents
1. [post=470752]What is a scanner?[/post]
2. [post=470794]Different types of scanners.[/post]
3. [post=470816]All-in-one's.[/post]
4. [post=470840]Terms to know.[/post]
5. [post=470842]How scanners work.[/post]
6. [post=474474]Connection interfaces.[/post]
7. [post=474481]Sources[/post]

 
What is a scanner?

1. What is a scanner?

flatbed.jpg

A scanner is a hardware used to import tangible media documents such as pictures or documents; it then converts this to a storable computer format so that the computer can understand. It does this by digitizing the image or document for colors, patterns, marks, and many other things; then stores the[post=470737]Top of page[/post]m in a format the computer can understand; such as an image format, .bmp, .gif, .jpg, etc. Depending on the scanner and type, it could recognize documents with prints or letter characters and put the information in an editable document file that you can manipulate or edit. In similarity, it reads the patters and marks on a picture, reproducing it as close as possible and storing it as an image file. Certain scanners have the ability to scan objects too, which will be discuseed later on.


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Different types of scanners

2. Different types of scanners.
  1. Flatbed Scanners
    flatbed.jpg

    There are the most common types of scanners that you will find sitting at a neighbors house, or on sale at an electronic reseller. They are usually the cheapest and most recommended value for a home, or small business use for the fact that it is very easy to operate and maintain. Like the image above, they are usually flat, thus the name goes and works similarly like a photo copier machine. These scanners usually have an opening flap at the top which flips open to reveal the sensor (usually CCD) and a large piece of glass sheet covering or almost about the same size of the scanner itself. Images or documents being scanned work by placing the picture or document face down onto the glass sheet and closing the lid. In the process of scanning the picture, the sensor moves from top to bottom scanning the whole area of that particular media and exporting the results to it's application which you should see on your computer screen.
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  2. Sheetfed Scanners
    sheetfed.jpg

    Now, a little smaller and a little different, sheefed scanners may look better and seem cheaper right? Well, these type of scanners were usually cheaper than flatbed scanners, however they weren't really reliable. Sheetfed scanners looks and operates similarly like a printer. Instead of having a moving sensor like flatbed scanners, their sensor head is stationed. When scanning, the picture or document is fed through the sensor head, and not the other way around. Good things about these scanners are that you can place several pictures or documents on the bay, and it will scan through all of them without you having to switch or put in the next picture; a very nice feature to have. However, the drawbacks are that this usually results in misfeeds and the possible potential to the media's geting stuck, which isn't really reliable. This could have caused damage to the medias if they were valuable to you. They also were usually limited to 400dpi since they're so small, so the quality isn't all that great.
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  3. Handheld Scanners
    handheld.jpg

    Probably the most uncommonly used of all scanners today. Handheld scanners were the "007" type where you needed it on the go to make a copy of heavily guarded documents. Cool as they sound, they are usually very hard to find in stores today because they really aren't the greatest of all available scanners. Like it's name states, it requires you to use your hand and manually move the scanner throughout the image or document. Like all humans, unless you have precise control and movement to every angle of the paper with your hand, this task isn't an easy thing to master. If you drag it a little too slow, a little too fast, a little off angle, your result will turn out cropped, wrong, or distorted. Not the best of all scanners, however this technology has been implemented into something more useful over the years. It has been used in stores to read off upc codes and scan items nowadays.
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  4. Card Scanners
    card.jpg

    You thought they didn't exist? Neither did I, I never knew of them.:D Anyways, these scanners are actually quite expensive, considering all they do is scan business cards. The idea is basically the same, you stick a business card in, and it spits it out the other end as a computer format you can edit or manipulate. They basically extract all the information from the business cards; such as name, address, contact information, etc. Then this information is stored and made available to you. Models come in both black and white, as well as full color scanners.
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  5. Single Sheet Scanners
    singlesheet.gif

    Similarly works like the Sheetfed scanners above. However, these scanners only reads a single sheet at a time. They aren't very common anymore and doesn't really produce high quality results. Made back in the earlier days, these types of scanners are probably obsolete now, but there might still be some floating around.
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  6. Drum Scanners
    drum.jpg

    Drum scanners are usually the mother of all scanners. They produce the highest quality result possible and are usually never found at your local electronic reseller. These scanners are usually used in professional printing businesses and sometimes by photographers. [FONT=verdana, geneva, helvetica]Drum scanners work in a very different manner than those previous talked about. The light source is in the middle of the drum, and the photocell's are on the outside. As the drum rotates around the object or media being scanned, it scans every point on a circle around it. The light and photocell's then move a fraction parallel to the axis of the drum for the next line to be scanned and recorded. The curved drum keeps the film to light source distance constant and steady, which in terms avoid problems with reflections and other mess. If you have the money, these scanners costs well in the XX,XXX or even more depending on your like. If you're an average user, this really isn't the one to look into.[/FONT]
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All-in-one's

3. All-in-one's

Why isn't this with "Different types of scanners?" Well, you wouldn't really consider any of these scanners so they wouldn't really fit in that category. These units usually have many features such as a printing feature, faxing feature, scanning feature, copying feature, and many more. An All-in-one (AIO) is really just a printer with a scanning unit with added features. The benefits of these units are that they save you a lot of space considering if you were to get a scanner, printer, fax machine, and copy machine. Another added nifty feature is that AIO units will allow you to scan and print right there and then rather than taking additional steps on the computer.

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Terms to know

4. Terms to know

Terms that you should really look into when purchasing a scanner for the first time. These terms and it's information should be what aids you in your choice of picking this scanner over that other one.
  1. DPI= (D)ots (P)er (I)nch:
    The resolution rating that is given for scanners. It refers to the quality of image that the scanner can produce. The higher this rating, the better quality the image. This is determined by a horizontal rating by vertical rating (4800x9600). The first number is the actual optical scanning quality of the scanner in terms of dots per horizontal line. The second number is the number of mechanical steps the scanner motor makes in an inch. So the optical lens can scan up to 4800 dots horizontally, and the motor can make 9600 steps vertically in an inch.
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  2. Scanner bit rate/color depth.
    This refers to the number of colors that the scanner can use to interpret the image that it is scanning. For example, a 24-bit scanner can use over 16 million colors, while a 48-bit can use over 281 million colors. If this seems strange, it because this is an exponential scale. Each bit refers to the number of bits/3 (cyan, red, yellow) that the scanner can use to describe a color. For 24-bit each of the three colors uses 8 bits each, while a 48-bit can use up to 16 bits each. For those of you that are mathematicians, you must use permutations/combinations to actually mathematically add up the total possible colors available.
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  3. Interpolation.
    Also a factor of resolution where the scanner extrapolates what a plausible dot would be between two other dots. Example: Two known dots are blue, so the dot between them would also be blue, this usually means a higher resolution, but possibly less accurate image.
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How scanners work

5. How scanners work

For the most part, pertaining to most scanners, except drum scanners.
As unique as they are, for the most part they work in very similar ways. A media file (document or picture) is placed face-down on a glass sheet made available when you open up a hinged panel which protects the glass sheet. A scanning array consisting of a lamp, a mirror, a lens, and an image sensor is booted up and at this stage, may take a while for it to warm up. When it is complete, the scanning process starts. The sensor moves back and forth underneath the glass making sure that all areas are scanned and recorded, even the area that you don't want scanned. Now, depending on the scanner, the sensor could either be:
  • 1. CCD - Charge Coupled Device - It converts the light being bounced off into an electrical current.
  • 2. CIS - Compact Image Sensor - Picks up the lights and darks from the scan.
18475795.gif

Image courtesy TASI (Technical Advisory Service for Images), United Kingdom (tasi.ac.uk).

Now, the CCD image sensor is a single row of sensor elements mounted on a moving platform which comes up very close to the media being scanned. Light from the lamp bounces off the original media above the glss sheet and is then reflected by mirrors on both sides into the lens. The lense then focuses the image into the CCD. Now, the CCD or CIS digitizes this information and converts it from analog-to-digital (ADC) then sends it to the scanner's internal workings. Lastly, the scanner sends this digitized format to the pc software, where you can view it as a readable computer format. So either CCD or CIS, they work similarly, but just read the data from the media differently. On flatbeds, you would usually find CCD sensors which moves to and about the glass sheet while on the sheetfed and those alike, you will find more of the CIS sensors which doesn't require the use of mirrors to bounce off the lights. For preference, the CCD usually perform better than a CIS sensor because everything is usually done within the sensor itself rather than have it bounced off lights. This, in-terms usually called for cheaper manufacturing and cheaper scanners; in all, cheaper quality and results that tend to be a little bit noisy as compared to CCD. That's why singlesheet, sheetfed, etc. type scanners are cheaper and produce poorer results.

When scanning color, the scanner sensor usuall take several trips back and forth; each time changing the color of the lamp. Scanning black/white images were fairly easy as it didn't need different colored lamps to display different colors. However, when color scanning was introduced, new ways of scanning were developed. Instead of just having one shade of lamp, there were now about 3 different colored lamps; Blue, Red, and Green. Each time the sensor passes the media, a different lamp was illuminated and the data is sent back to the scanner to compile. When it was done, this compiled data was digitized and sent to the pc where you can now see it as a readable computer format. Eventually, people were getting impatient and couldn't stand the wait of having the scanner go back and forth 3-4 times and sometimes getting stuck along the way. So, a newer method was introduced. This time, light sensitive CCD/CIS sensors were produced where it was able to recognize the different Blue, Red, and Green hues, so it eliminated the wait time for those impatient owners.

Drum scanners
Working in a different way than what was just described above, drum scanners spins your media or object rather than scan it. The media is placed on a cylindrical drum (how it got it's name). A small path of light is shined on the media and when the drum spins, the light is moved a line of pixel at a time. Now, this whole process involves PMT (Photo Multiplier Tubes); PMT are used because they are more effective than CCD or CIS because they can pick up the darker/lighter/shadows more effectively and give you a much accurate read of the media. In the case of the CCD or CIS, they would just register this as dark or light, but not anything inbetween.


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Connection interfaces

6. Connection interfaces
  1. ISA/Parallel
    Cparallel.jpg

    -*couldn't find an isa adapter picture.
    Probably the very first connection type for scanners. Even when it was made, most pc's didn't have any available adapter to connect to besides the printer port. These adapters weren't originally made for scanning, so the data and information being sent back and forth through it was slow. The next idea was a custom adapter on an ISA card. Even now, most pc's didn't have this and most scanners sold at this time came with it's own custom adapter on an ISA card that needed to be installed.
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  2. SCSI
    Cscsi.gif

    Known more commenly on a mac, the SCSI was the next available option for scanners since ISA/Parallel ports weren't really working out too good. However, this also raised another issue since the SCSI adapters were suppose to be on a mac only, most pc's didn't have any. Again, in this time period, most scanners sold came with one of these that has to be installed. So, if you had no spare slots or no other available IRQs for it to use, you really have no choice. You either needed to drop down to printer port or a custom ISA card. There wasn't really much options or other ways because technology haven't advanced far enough yet...
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  3. USB
    Cusb.jpg

    Fast forward a couple years or so and the USB port was introduced. Unlike SCSI, ISA, and Parallel, most pc's came with USB now. It was as if it was the standard for each pc should have atleast one. The USB ports were small and efficient and required no real know how since it is usually plug and play. When installing a scanner for the first time, it's as easy as supplying the right driver for the scanner. USB's were far more effective and faster than any other previsouly mentioned; another thing to note was that USB was able to provide power. At some point, manufacturers were making scanners that run straight off the USB and the pc's power with no need for any other plug to the outlet. However, this wasn't as efficient as giving the scanner it's own source of power, so it was quickly thrown out. Nonetheless, this is not saying that this method doesn't exist anymore; but merely as USB technology has improved, USB-powered scanners have begun to be re-introduced; especially card scanners and other smaller scanners whic do not require tons of power to operate.
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  4. Firewire
    Cfirewire.jpg

    Lastly, or probably produced about the same time, firewire was introduced to the market too. Firewire were an improvement over USB with speed and effeciveness of the image qualities. Firewire connections were able to handle 400 megabytes per second, but were usually found on the higher-end scanners with a pricier price tags. Now generally, firewire linked scanners are able to produce better quality outputs as they are able to transfer more digitized data from the scanner to the pc.
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