Scanning an Image

There are so many scanners out there, it is almost impossible to make a decision. You want to know that you got the best quality for the best price.

How do you know if you got a good scanner? Well it depends on what you want to do with your scanned images. Do you just want to archive some documents or do you want to scan high resolution images for processing.

Once you made your decision on how you plan to use your scanner, now you need to know the differences in scanners. Some scanners have light that passes the copy four times to make CMYK files. Other scanners scan images in one to three passes to make an RGB file.

Scanners use one of two types of input technologies: charge-coupled device (CCD) and photomultiplier tube (PMT).

CCD scanners have an array of phtosensitive diodes. When light hits the array, the diodes give off charges proportional to the levels of light. The charges are digitized and the diodes' output values become part of the image data.

PMT scanners, also known as drum scaners, are like television tubes in reverse. A television tube emits light when charged, while a PMT emits an electric charge when light hits it. The photomultiplier tube sends the charge to an analog-to-digital converter that changes the engergy into digital data.

A scanner should use at least eight bits per channel and be capable of high resolution, density range and dynamic range.

When a scanner is 2,400-ppi, try to think spots per inch and not pixels per inch.

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