Hello Everyone,
It's been great hearing about your increased business in wide format scanning over the last few months. You've had great successes with the Colortrac SmartLF Cx 40 alone as well as in combination with a variety of printers to create innovative MFP solutions.  With the introduction of the Colortrac SmartLF Gx 42, we've had several requests for a brief explanation about CCD versus CIS imaging technology that you can pass on to your customers. Read below and for more information and literature, visit our website www.geiwideformat.com.

CIS SCANNING TECHNOLOGY....

CCD SCANNING TECHNOLOGY...

 

What is the difference between CCD and CIS wide format scanner technology ?

What is the best choice for my large format scanning application, CCD or CIS ?

Traditionally, most large format scanners have used CCD technology to capture the digital image.  Now, the latest advances in CIS technology have created opportunities for leading edge manufacturers to design wide format scanners that offer similar performance – scan speed, image quality, resolution & image width – comparable with, or, in some respects, exceeding, the older CCD technology based large format scanners.

Ultimately the decision between CIS and CCD will depend on what you want to do with your large format scanner and how much you want to spend.  The basic differences between CCD and CIS imaging technology are described in the notes below.  They will help you choose the right type of large format scanner for your application.

Large format scanners using CCD technology will give you an image with a relatively-wide color gamut and a relatively-high dynamic range.  Color gamut is a measure of how wide a range of different colors the scanner can capture accurately.  Dynamic range is a measure of how much detail the scanner can see in dark areas before "blacking out".  If you wish to scan photographic-type material and you wish to achieve the best possible reproduction in terms of color integrity and shadow detail, then a CCD scanner is the one for you.   CCD scanners also offer greater depth of field, so if your specialization is scanning books and you want to minimize image deterioration towards the open spine, then choose a large format flatbed scanner which uses CCD technology.   

Large format scanners using CIS technology will give you an image with relatively-high resolving power  and potentially higher geometric accuracy.  Resolving power is a measure of how well the scanner can see thin lines or edges.  Geometric accuracy is a measure of the spatial accuracy of the image compared to the original document.  If you wish to scan black-and-white or color technical documents (such as drawings, maps etc), and you wish to achieve the best possible reproduction in terms of line definition and accuracy, then a CIS scanner is the one for you.  CIS scanners also have a far-shorter warm-up time and are far-more compact & lightweight, so if you want to be mobile and switch on and start scanning immediately, then CIS technology will enable this.

Of course, CIS scanners provide acceptable color gamut and dynamic range for most users, just as CCD scanners provide acceptable resolving power and accuracy for most users.

So, while the performance of a CIS wide format scanner is similar to that of CCD, it is not the same.  For a majority of owners who will use their large format scanner for AEC, CAD and GIS applications, CIS wide format scanners can offer some major advantages.

 

 CCD Technology

A Charge Coupled Device (CCD) senses light that is incident on its silicon surface.  This surface is divided into discrete square cells, each several microns across (e.g. 5.25um).  In a document scanner, the CCD will have a line of, say, 5000 cells (or pixels).   For color scanning, the CCD will have 3 or 4 closely-spaced parallel lines of pixels, each line being overlaid by a different color filter. 

Now consider the geometric requirements for a CCD scanner.   To produce a scanner with 400 dpi optical resolution, the scanner manufacturer needs to design an optical system which focuses light from a 1/400" square pixel at the object (document) onto a 5.25 um square pixel at the CCD silicon surface, i.e. a reduction of approximately 12:1.  This is done using photographic enlarger lenses and, most likely, mirrors to fold the optical path into a reasonable space.   The use of such lenses and mirrors will introduce some geometric distortion and some limits on focus, thereby effecting geometric accuracy and resolving power.  The magnitude of these effects will be determined by the performance of the lens and the mirrors and how much the manufacturer is prepared to pay for these key components.

The manufacturer of a CCD scanner must also design an illumination system, generally using one or two fluorescent tubes.  Because the manufacturer controls this illumination, and is able to apply  proprietary processing to the CCD output, it is possible to optimize the color gamut and the dynamic range of a CCD scanner.  The color content is determined by using a "white" light (controlled by the scanner manufacturer) combined with colored filters within the CCD (controlled by the CCD manufacturer).

The use of fluorescent tubes does mean that a warm-up period is necessary, to allow the illumination levels to stabilize as the fluorescent tubes heat up.  The need for frequent re-calibration of a CCD scanner is also mainly due to variations in illumination.

CIS Technology

A Contact Image Sensor (CIS) is an integrated module that comprises an illumination system, an optical system and a light-sensing system – all within a single compact component.  

The light-sensing system is the silicon surface which is divided up into (e.g. 5000) discrete square cells, the size of each being a fraction of an inch depending upon the required scanning resolution (a 400 dpi scanner will use a CIS whose cells are 1/400" across).   The optical system is a rod lens array that directs light from the document surface onto the silicon surface.  Such an optical system is 1:1, i.e. there is no reduction or enlargement; and this results in a scanner offering the best performance in terms of resolving power and geometric accuracy.

The illumination is provided by Light Emitting Diodes (LEDs) shining down a light guide which in turn directs the light onto the document.   There are three LEDs (red, green, blue) which are strobed rapidly,  thereby providing the color content in the scan.  Note that there are no color filters in the optical or light-sensing system.   The color gamut of a CIS scanner is therefore determined by the spectrum of each of the LEDs, rather than by color filters as is the case with CCDs.  Because color filter technology is more developed than LED spectrum technology, a CIS scanner will not provide as wide a color gamut as a CCD scanner.

However, rapidly-strobed LEDs require no warm-up period.  Therefore, a CIS scanner can be switched on and used immediately.  Further, LEDs are very stable which means that a CIS scanner does not require frequent re-calibration.

We hope this information helps in your sales efforts and please don't hesitate to let us know of any wide format technology questions you have.