A scanner works very similar to a photocopier or a fax machine. They both work in similar manners because they both read, or scan , a paper document and copy the document. A photocopier scans the document and then sends the output (information that was scanned) to a printer and prints out a copy of the document. A fax machine scans the document and sends the output accross the telephone line to another fax machine, where it is printed by a thermal printer in the fax machine the document is being sent to. A scanner scans a document and sends the output to a computer via paralell or SCSI port. The scanner output is then interperted by a graphics program, like Adobe Photoshop, and the image, or text will be displayed.
Unlike photocopiers and fax machines, scanners can scan an image at a wide range of qualities. This quality is uasaully measured in dpi, or dots per inch. The higher the dpi, the better the image. This is because the higer the dpi gets, the closer together the dots get to each other. Similar to resolution, when the dpi increases, so does the image on the screen but, still prints out at its original size. For example, if you scan a dollar bill at 2400 dpi the image will be so large that George Washington's eye will take up about one fourth of the screen but, when the image is printed it will be the same size as the dollar bill you scanned (please note that it is illegal to print any american currency without a visiable marking on the copy to alow people to know the copy is not real currency, if this is not done you could be arrested for counterfitting).
A scanners scanning capability is not just measured in dpi but can also be measured in resolution. A scanner may have a 2400 x 2400 optical resolution scanning capaiablity but, it can also scan at 9600 x 9600 maxium. What does this mean? Well, lets say you have a scanner that can not scan anything larger then a 8 1/2" x 11" peice of paper. Then, you go and scan a 8 1/2" x 11" peice of paper at 2400 dpi. You then view the scan and see that the entire paper was scanned. Then you decide to scan the same thing at 4800 dpi. When the image is scanned you find that only one half of the paper was scanned. Why did this happen? This happened because the maxium optical resolution for this scanner is 2400 x 2400. So if you scan anything and the dpi is higher then 2400 you will not be able to scan an entire 8 1/2" x 11" image. But why did only half of the image come out when it was scanned at 4800 dpi? Because 4800 the twice the amount of 2400. As you go up from 2400 dpi the scanning area gets smaller. For exapmle, if you scanned the same image again but this time at 9600 dpi you would only get one fourth of the image because 9600 is four times the amount of 2400. Thus, the maxium optical resolution is how high the image quality of the scan can get within the entire scannable aera, while the maxium resolution is how high the image quality of the scan can get regardless of how big of an area you can scan.
If you still have any other questions regarding scanning, or if you are just completely lost, feel free to e-mail Digital Photography Exposed at email@example.com
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