Scanner technology - the need-to-know stuff

CCD Technology

CCD stands for Charge Coupled Device, which is a type of technology first used in imaging by astronomers and is also the mainstream technology used in today's digital cameras. The charge coupled device accepts light and converts it to electrical charges that are then stored and manipulated into digital images. It has had over 20 years of development and started becoming popular as mainstream scanner technology in the middle of the last decade. The net result was cheaper, lighter scanners than those previously available, although the scan quality was initially not as good as the incumbent CIS technology scanners (this is no longer the case).

CIS Technology

Contact Image Sensor (CIS) technology used to be the mainstream technology for flatbed scanners. It is not as popular today as it once was. Scanners using a Contact Image Sensor are usually larger and heavier than those using CCD technology.

TWAIN Driver

One of the most important yet overlooked aspects of a scanner, the TWAIN driver is the piece of software that allows the scanner to do its thing on your computer. Almost every scanner has a TWAIN driver (TWAIN stands for Toolkit Without An Interesting Name). The capabilities of your TWAIN driver will affect other software, be it third party or bundled with the scanner.

As it is almost impossible for you to test every single TWAIN driver available, your best recourse is to read as many scanner reviews as you can.

The driver is the first point of call for the information that comes from the scanner to your PC. It is the software that allows you to determine the basics such as which resolution you are scanning at and what type of image or document you are scanning. Effective TWAIN drivers will also work as mini image editing packages, allowing you to at least crop, rotate, shrink or enlarge an image. Some have additional features such as contrast, brightness, gamma correction and other filters.

The bottom line is that the more effective, diverse and user-friendly your TWAIN driver is, the less potent your image editing or OCR software spend needs to be. The other advantage is that the greater the depth of detail the TWAIN driver can offer, the less work will be required on the image when it is transferred to the image editing software. Your scanner may be perfect from a hardware point of view, but if it ships with a crappy TWAIN driver it can make the scanner a tedious device to use.

Optical Scan Resolution

Scan resolution is one of the differentiators you will encounter when checking out scanners. There are usually two figures quoted and the more important one is optical resolution. Optical resolution of an A4 scanner refers to the number of dots of information into which that the scanner can convert the image. Basically, the greater the optical resolution scan, the higher quality output image you will get. This is vital if you will be scanning images to be enlarged or if you scan a small image and you want to enlarge it so you can edit out flaws. So, the bottom line is that the higher the optical resolution, the better the scanner technology.

Common jobs that scanners do

Scanning photographs for:

  • Resizing, reprinting, repairing
  • Digital backup (archiving)
  • Image editing
  • Web or desktop publishing

Scanning slides, transparencies, x-rays for:

  • Resizing and printing
  • Digital backup (archiving)
  • Image editing
  • Web or desktop publishing

Scanning documents for:

  • Digital Backup (archiving)
  • Data entry via OCR
  • Editing
  • Web or desktop publishing

Scanning barcodes for:

  • Point of sale
  • Warehousing and stock take

Entry-level scanners priced up to about $200 will provide optical resolutions of at least 600x1200 at 48-bit. As the price increases, so does the resolution. Do not be frightened by this because as little as a $300 to $400 outlay will buy you a scanner with optical resolutions of 2400x4800 at 48-bit.

Interpolated Scan Resolution

This a scan resolution that is always higher than the stated optical resolution and is achieved by the use of software. Interpolated Scan Resolution refers to the number of dots of information that the scanner can produce from an image by the use of clever mathematical software that takes the existing number of dots that the scanner is capable of via optical resolution and increasing it. So when the salesperson quotes you the resolution the scanner is capable of, be sure that they are not quoting the interpolated resolution.

Bit Depth

A bit is the smallest piece of information that a computer will handle. Bit depth refers to the amount of information each pixel (dot) can carry - and all images are made up of pixels. It can become quite confusing to sort out the technical details of how it works, but there are some good maxims that you can adhere to without having to know exactly what they means.

  • More bit depth translates into better output because more layers of information exist in the scan.
  • More bit depth means larger file sizes. For example, if you scan a normal colour photograph at, say, 300dpi resolution, first at 24-bits and then at 48-bits of depth, the 48-bit scan will have a much larger file size even though the scan resolution is the same.

In summary, the things you need to remember about bit depth when buying a scanner is that the greater the bit depth, the better the quality of the scan and the larger the file sizes. For almost all types of general-purpose use, 24-bit external colour depth is sufficient.

An example of how to set bit depth.

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