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computerhakk · 10-26-2006, 07:34 AM

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.

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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10-26-2006, 07:34 AM	#6 (permalink)
computerhakk VIP Member Join Date: Aug 2005 Location: THOJhakk county Posts: 3,634	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. 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. Top of page __________________ "Remember, wrong advice may be worse than no advice at all." ::COMPUTERHAKK::: Last edited by DCIScouts; 10-26-2006 at 07:38 AM.