Over the years we have received many enquiries from our Scan2CAD raster to vector conversion software users for an A2 / C-size wide format scanner with which to scan monochrome CAD technical drawings and or CNC shapes and profiles.

Most enquirers expect such a medium-size scanner to be affordably priced and widely available. However, typing “A2 / C-size scanners” or “find the best A2 scanner” into Google just doesn’t come up with anything helpful. Any investigation will show that A2 / C-size large format scanners are as rare as hen’s teeth – and consequently very expensive!

Because an A2 / C-size scanner is only one size up from relatively inexpensive A3 / B-size scanners, (and two up from the ubiquitous and cheap A4 / A-size desktop scanners), many enquirers after these devices assume that the cost of an A2 / C-size scanner will be proportionate to the smaller sizes. Generally, they expect the cost of an A2 / C-size scanner to be no more than two or three times as much as an A3 / B-size scanner. When they are able to find an A2 / C-size desktop scanner, they are shocked to discover that the cost of A2 / C-sized scanning is much higher than expected.

Historically, the large format scanner manufacturers have found that A1 / D-size scanners are not as popular among CAD users as A0 / E-size ones. This is because a larger A0 / E-size wide format scanner offers the buyer a more complete, professional scanning solution than one whose upper limit is smaller A1 / D-size drawings. At the back of every large format scanner manufacturers’ mind lurks the question “if A1 / D-size scanners do not sell, why should A2 / C-size ones?”

To date, the CAD, CNC and other professions have not indicated that there is a big enough market for an A2 / C-size large format scanner to be a profitable manufacturing exercise. Largely for this reason, A2 / C-size scanners do not exist as CAD / CNC scanning solutions.

Those A2 / C-size flatbed scanners that do exist are aimed at capturing artwork, newspapers, fragile originals, books and other thick or delicate materials. Mostly used in libraries, museums and educational institutions, their market is small compared to the one for CAD scanners. As a result, the manufacturers tag these specialist A2 / C-size scanners with a high sales price. They do not expect CAD or CNC users to buy them. They expect CAD and CNC users to buy A1 / D-size scanners or better, A0 / E-size ones.

Both Colortrac and Contex have recently released new models of attractively priced A1 / D-size scanners. Both Colortrac (24″ CIS and 28″ CCD) and Contex (24″ CIS) offer A1 / D-size scanners which cost less than the two A2 / C-size desktop scanners we’ve identified (see our article At last, more affordable A1 / D-size scanners!).

CIS (contact image sensor) best suits technical document scanning in more affordable scanners; CCD (charge coupled device) is the longest serving optical imaging technology. It best suits color graphics capture but is expensive. The main suppliers of A2 / C-size desktop or flatbed scanners are Contex and Image Access. Both their offerings are CCD-based, providing a professional color capture solution for scanning artwork and manuscripts, etc., and making them generally too expensive for most CAD and CNC users simpler needs.

Image Access WideTEK 25
Flatbed; CCD imaging technology; 1200 x 600 dpi optical resolution; 25 x 17.7″ (635 x 450 mm)

List Price: GBP £7,295.00 USD: $10,999
Image Access web site
Allied Images web site (UK distributor)

Contex FLEX50i
Flatbed; CCD imaging technology; 400 dpi optical resolution; 24 x 18″ (610 x 457 mm)

List Price: GBP £6,750.00 USD: $11,600
Contex web site
Art Systems web site (UK distributor)

Prices at 22nd February 2010.

SUMMARY
Geared to color graphics, neither the WideTEK 25 nor the Contex FLEX50i are ideal for CAD or CNC usage. Today, CAD users can buy a bigger, more useful A1 / D-size scanner for a lot less than the cost of these two smaller A2 / C-size desktop devices.

To be fair, while both the WideTEK 25 and the Contex FLEX50i can be used for CAD work, neither are intended to do so. Both are very expensive and bear no relation to the cost of an A4 / A-size or A3 / B-size scanner. Being slap in the middle of standard ISO / ANSI paper sizes, they offer the least practical scanning solution to the majority of CAD users who usually work to bigger paper sizes. At present, (22nd February 2010), there appears to be no A2 / C-size desktop scanner available for the mass market, CAD, CNC or other.

So, what is the best A2 / C-size scanning alternative?

Today, CAD and CNC users can buy a bigger, more useful A1 / D-size scanner for a lot less than the cost of the smaller Contex and Image Access A2 / C-size desktop devices. This can offer some benefits.

The following event unfolded recently.

An engineer contacted Scanners4CAD thinking it sold scanners. (It doesn’t – it is a large format scanner news and advice site.) He said that he had looked but had no luck finding an A2 / C-size desktop scanner. Could we recommend one?

He was a CNC user cutting relatively small parts, like gaskets and profiles, etc., often to slightly bigger than A3 / B-sizes, occasionally even to bigger sizes. When he needed to scan to A1 / D and A0 / E sizes he went to a scanning bureau service. He did not need a fancy color capability, he said. A monochrome (black and white) A2 / C-size scanner would do.

We explained the limitations of A2 / C-size scanners and pointed him to both the WideTEK 25 and the Contex FLEX50i. He quickly lost his interest in these A2 / C-size wide format scanners when told the price. Next, we pointed him in the direction of A1 / D-size scanners. Given the cost of buying an A2 / C-size large format scanner, he quickly realized that the most cost-effective purchase he could make was to buy a bigger size of scanner.

After we explained the limitations of Colortrac and Contex A1 / D-size (24″) scanners – he would never be able to scan a larger A0 / E-size technical document when he needed to – we suggested he take advantage of some incredibly good offers being made on A0 / E-size large format scanners at present. This he did. We understand that he bought a 40″ wide Colortrac SmartLF Ci 40m (monochrome) scanner (upgradeable to color) for, he said, “about half the cost of the A2 / C-size flatbed I was quoted on”. And, he added, “I will now never need to leave the workshop to visit a scanning bureau service again”.

A few years back we conducted a survey of our Scan2CAD users to find out what they wanted in a large format scanner. To our surprise, almost half said that an A1 / D-size wide format scanner would meet their needs. Price, as always, was the sticking point. Most wanted to pay no more than a low GBP £1000 / USD $1500.

The good news is that there are now two new 24″ wide, (A1 / D-size) CIS-based (contact image sensor) wide format scanners available, both suited to scanning technical drawings for the purposes of raster to vector conversion and more besides. Both make A1 / D-size scanning available at an unprecedented low price. However, both are more expensive than our highly cost-conscious Scan2CAD users stated they were willing to pay.

The two new 24″ wide-format scanners are the Contex XD2490 and the Colortrac SmartLF Ci 24. Both are based on wider models which have won BERTL 4.5 Star “Outstanding” awards. (We do not place much value on BERTL awards or ratings.) The best evaluation of these devices will be your own using the drawings you have on file. As most resellers still expect to give a hands-on demo, arranging an on-site evaluation in your office should not be difficult. Both the Contex and Colortrac 24″ wide devices are compact and lightweight and well-suited to transportation.

The Contex XD2490 comes in at GBP £2775 / USD $3970, is fully color capable and is the only 24″ model in the range. There are three Colortrac SmartLF Ci 24s – m (monochrome), c (color) and e (enhanced or faster color). The SmartLF Ci 24e costs GBP £2895 / USD $4250. Both are supplied with scanning software, the XD2490m including Nextimage SCAN. The more powerful Nextimage SCAN+COPY is a paid for extra. The SmartLF Ci 24 is supplied with the basic SmartLF All-in-One scan, copy and email software. ScanWorks and CopySmart are paid for extas.

We have tested both these devices’ wider stablemates, the 44″ wide Contex SD4490 and the 40″ wide Colortrac SmartLF Ci 40e. These CIS wide-format scanners are both well-suited to scanning technical documents, drawings and maps up to A0 / E-size in monochrome, grayscale or color. There is no reason why the smaller Contex XD2490 and the Colortrac SmartLF Ci 24 should not provide similar quality scans to their full-sized stablemates.

The biggest downside of both these 24″ devices is that neither will let you scan an A0 / E-size drawing should you need to do so. This limitation is the reason why less expensive 24″ scanners sell in smaller numbers than their wider, more useful, more expensive counterparts. Give your purchase of a 24″ scanner some serious thought!

The fundamental difference between these 24″ scanners is their design. As a cut-down version of Contex’s first generation of CIS-based SD Series scanners, the XD2490 uses a traditional scanner design based on multiple rollers. These draw the document horizontally into and through the scanner from the front to exit at the back. The SmartLF Ci 24 is based on Colortrac’s fourth generation Ci 40 model and is the more innovative of the two devices. It uses a single, solid roller or drum to draw the document in and roll it around the drum. Uniquely, the document exits at the front of the Ci 24, not at the back, as in every other make of scanner available today.

What front versus back media exit boils down to is that the SmartLF Ci 24 can be used more practically as a desktop scanner. Ironically, this is the role for which Contex suggests the XD2490 is best suited. Indeed, because Contex sees the XD2490 as a desktop scanner, it is not offering the option of a floorstand at present, presumably to keep the total cost down. Colortrac offers the SmartLF Ci 24 with the option of a professional floorstand, albeit for the not inconsequential added cost of GBP £345 / USD $500.

The XD2490’s traditional rear exit media path means that it will eject the document out the back and over the desk which must be cleared before it can be used for desktop scanning. If your desk is anything like mine, clearing it is an unwelcome job at any time but most especially at short notice. The solution is to place the XD2490 on its own dedicated surface or on the the far side of a desk so that it feeds paper over the edge. (It has the option to hold the paper and rewind it.) However, such positioning may not make the best use of available space in a small office.

By comparison, the SmartLF Ci 24’s front exit makes it more practical to use as a large format desktop scanner. Quite simply, the SmartLF Ci 24 requires no clear desk space behind it at all. If the SmartLF Ci 24 is placed on the front edge of a desk, its operational workspace occupies no more than the area taken up by its footprint. This allows it to be placed and used in confined spaces previously inaccesible to wide-format scanners, like on top of a cabinet, in a bookcase or on a shelf mounted on a wall, etc. However, before you mount your new SmartLF Ci 24 on a purpose-built shelf, you must ensure that the shelf is wide enough to allow its hood to open fully. The SmartLF Ci 24’s hood opens backwards, taking up extra space. Failure to provide a wide enough shelf (mounted at a suitable height) may mean having to take it down every time it needs to be opened.

The main consequence of the SmartLF Ci 24’s design is that it accepts slightly thinner media than the XD2490. The SmartLF Ci 40 and Ci 24 are restricted to a maximum of 270gsm technical document media or a thicknesses of only 0.012″ (0.3mm). The maximum media thickness of the XD2490 is 0.08″ (2 mm). Some readers may be perplexed by this and worry that some technical documents might be too thick for the SmartLF Ci Series. In our experience, we have not yet found a technical document drawn on standard drafting media that is too thick for the Colortrac SmartLF Ci Series to scan. Surprisingly, 0.012″ (0.3mm) thickness covers almost all documents.

As stated, 24″ scanners are unpopular because of the ever-present risk that they will not be able to scan larger drawings. Contex are aiming the XD2490 at AEC professionals, many of whom use smaller size architectural and construction drawings. Contex are making much of the XD2490’s ability to act like a glorified fax machine for the digital age, emailing revised and scanned documents back and forth between site and head office and or between designer and client. This is an entirely practical application for some AEC professionals with smaller drawings but it is nothing new. All scanners today have a scan-to-email facility that saves documents as a PDF file for emailing.

The two devices have different maximum optical resolution, generally regarded as an indicator of image sharpness. Both offer all the image sharpness you will need for producing good quality scanned images suitable for archiving, viewing, printing, emailing but, most especially, raster to vector conversion. The XD2490’s 1200 dpi optical resolution is far more than you can practically use and twice as much as the SmartLF Ci 24’s 600 dpi which is still more than you are likely to use. In reality only the uninitiated will scan an A1 / D-size document at 1200 dpi or even 600 dpi in monochrome, let alone color. The resulant file will simply be too big.

Raster to vector conversion requires sharp, clear, well-defined images. Many new to raster to vector conversion and or scanning are wrongly led to believe that only high optical resolution can give scanned images the necessary degree of sharpness and detail which is needed. This is untrue. Generally, when performing raster to vector conversion on most technical drawings, you will seldom, if ever, use optical resolution any higher than 400 dpi. The only practical benefit from 1200 dpi optical resolution is in scanning small postcard or smaller size images.

Both devices are adequately fast. Contex claim that their high scan speeds increase productivity. This claim is only true when saving low resolution images for archiving, viewing or printing purposes. It is untrue when scanning for raster to vector conversion (or for quality images) where slower, more deliberate scans using editing tools must be made in order to get the best vectorization results. (See Auntie’s Ghastly Gallery for examples of what can happen if you don’t scan with care and attention to detail.) Good quality scans require fast and flexible scanning and post-scan editing tools. Colortrac’s ScanWorks software, while long-in-the-tooth, uses an intelligent “scan once, edit many” approach which, in our view, provides the best way to get sharp, clean scans that vectorize well.

Support for Gigabit Ethernet connectivity allows the SmartLF Ci 24 to easily connect to most office networks. Although the Contex XD2490 does not have Ethernet connectivity, it is supplied with a special driver that makes it easy to set up and use over a network.

These 24″ models offer similar levels of price and performance and, as they are based on successful wider stablemates, pedigree. However, the comparative newness of both the Contex SD Series and the Colortrac SmartLF Ci Series means that neither system is yet old enough to claim that its technology is fully proven. Nevertheless, expect to see these products representing Contex’s and Colortrac’s main technical document scanners for some years to come.

In their advertisements and sales literature the large format scanner manufacturers all claim that their scanners are fast, easy and productive.

We must disagree. We receive hundreds of poorly scanned images every year which are totally unsuitable for raster to vector conversion. Clearly, the people who made these scans did not have a clue. If scanners are so easy and productive to use, why then the plethora of poor quality scanned images?

Essentially, there are three issues.

• Many users (and many large format scanner resellers) do not know what good scanned quality for raster to vector conversion is.
• Many users do not know how to go about achieving a good quality scanned image for raster to vector conversion.
• The large format scanner being used may be equipped with poor quality or difficult to use scanning software, which makes achieving a high quality scan much more difficult.

There is a need for basic training which shows the user what  good scanned image quality is.  Showing someone how to scan is pointless if that person does not know what they are attempting to achieve.  Raster to vector conversion software requires sharp solid lines on a clean white background. It might sound easy enough but without zooming in to interrogate the scanned image, the result may be nothing of the sort. Learn to interrogate every scan you make.

Without some proper training, many new and even long-term users find large format scanning difficult, time-consuming and overly complicated. Many will accept the first result they get rather than persist in spending more precious time trying to get a sharper, cleaner, better image. Because time is money, the least skilled and competent are often tasked to do the scanning after only the briefest of  introductions to the process. No quality scan will come of this.

Getting a Demo

All large format scanner manufacturers supply their own proprietary scanning software. None work with other scanners. You are a prisoner of the software supplied with your choice of wide format scanner.

We recommend that you examine the supplied scanning software with a critical eye. It is the front-end of every scanning solution that you will have to work with. Some scanning software programs are decidedly better than others for creating scans suitable for raster to vector conversion.

Getting the best system for your needs means looking at more than one large format scanner – and its software! As viewing more than one scanning system is usually a hassle for busy people, many will buy the first scanner they see if it is well demo-ed to them. It is tempting but try not to make this mistake! Given the competition in the scanner market, it is not difficult to arrange demos from rival suppliers. Try to make the time to do so.

Most large format scanner sales people have their own tried and tested demo routine into which they throw a few tricks calculated to impress you. It is important that you take charge of their demo. Do not let them use their drawings. Use the worst of your own drawings while trying to use the software yourself. As far as possible, turn their demo into a training session. Did you learn enough to use it alone in 10 days time?

Try to learn as much about scanning and scanned image quality as you can when you get a large format scanner demo. Tell the demo jockey that you want to scan drawings for raster to vector conversion. Ignore any who say "raster to vector conversion doesn’t work".  Press them to provide the sharp, clean scans which they claim in their product literature. This is what you will need in a large format scanner for raster to vector conversion.

Most importantly, does the reseller understand scanned image quality? We cannot stress how important scanned image quality is. In scanning a monochrome (black and white) drawing for automatic raster to vector conversion, lines need to be sharp and well-defined against a clean white background. This can only be seen by zooming into the image, cleaning it up and making adjustments to the settings. How easy is it to zoom in?

Was the large format scanner salesperson able to show you how a dirty drawing can be cleaned up so that it has sharp lines which will vectorize well in a raster to vector converter like Scan2CAD? Was it an easy matter to get a better result? Did this require a lot of tedious and time-consuming rescanning? Or did the salesperson use an easier, cleverer way to do this?

Thresholding

Having a clean white background with well-defined, unbroken drawing detail is what one aims for when scanning for raster to vector conversion.

As a result, the main features we look for in scanning software are simple and adaptive thresholding, features which allow you to dynamically clean the drawing background while at the same time strengthening the foreground drawing detail. A number of packages offer this, including our own raster to vector converter, Scan2CAD.

Graphtec’s Scanning Master software has thresholding which it calls Intensity Correction. While it works well, it is made difficult to use by the software’s rocker mode. If the scan needs to be improved, you must typically zoom into a part of the image in order to see the effect of changes to the scan settings. To do this, Graphtec scanners must feed the document back and forwards through the scanner which shows the results in a very small and narrow on-screen window. It is a slow, outdated way of scanning.

Both Colortrac’s and Contex’s scanning software offer thresholding which is easier to use. However, Contex’s Nextimage software requires a prescan and a rescan and what you see in the final scanned image is not necessarily the same as what you saw in the prescan.

We think we have good reasons for recommending Colortrac’s ScanWorks software. Its “scan once, edit many” approach is different to and more productive than anything else we’ve used. ScanWorks requires just one scan, (unless you need to change the resolution). Thereafter, you can change settings and see the results dynamically in real-time without any need to rescan. There is no backwards-forwards rocker mode scanning, allowing you to create scans suitable for raster to vector conversion relatively quickly and easily (assuming that the original drawing is itself high enough quality).

For more information on thresholding, see Explaining the threshold – a vital setting for successful raster to vector conversion.

Other Considerations

There are other issues which you may want to consider, like image width, ENERGY STAR® compliance and price.

Large format scanners vary in width from 24″ (scans up to A1 / D-size drawings in portrait) to 56″ (scans A0 / E-size drawings in landscape). Most scanners are in the 36″ to 44″ range and can scan A0 / E-size drawings in portrait.

Most modern scanners now use instant-on LED illumination and are ENERGY STAR compliant. LED illumination and ENERGY STAR compliance do not affect image quality for raster to vector conversion. However, they do affect the speed with which you can walk up to a scanner, switch it on and scan. Left running, ENERGY STAR compliant scanners will go into a cost-saving sleep mode.

Large format scanners that use CIS technology generally cost less than CCD scanners. CCD scanners are better for high quality color scans, but are not necessary for scanning drawings for raster to vector conversion. Contex SD, Colortrac Ci and Graphtec CSX300 CIS-based large format scanners are the most affordable. As stated, it is the software which provides the sharpness and clarity needed for raster to vector conversion.

Some manufacturers / resellers include software for free, while others charge extra. Many manufacturers / resellers are now also including an on-site warranty in the price of their scanners.

Wrapping Up

Don’t get drawn in by sales hype: All current large format scanners have the optical resolution and speed required to create a scan that is suitable for raster to vector conversion.

Scanners that use CIS technology generally cost less than CCD scanners, and so are recommended if price is an issue.

Considerable thought needs to be given to the accompanying software. If the scanner you want to buy has poor scanning software, creating a suitable scan for raster to vector conversion will be more difficult and will take longer.

A way around poor scanning software is to use your scanner’s software to scan in grayscale, then use Scan2CAD’s simple and adaptive thresholding to turn the scan into a usable black and white image suitable for raster to vector conversion.

For further information on the latest large format scanners and to download a large format scanner comparison chart, see www.scanners4cad.com.

The two areas of large format scanner sales most clouded in bull and misrepresentation are Resolution and Speed.

Optical Resolution

Optical resolution is the resolution at which your drawings are actually scanned.

The leading high-end scanners are over-specified in terms of optical resolution, i.e. they give you more than you can practically use.

Contex’s SD Series CIS scanners offer true 1200 dpi optical resolution, the same as Colortrac SmartLF Gx+ CCD scanners. To those new to large format scanning, this possibly indicates that these devices are the best in their categories.

True 1200 x 1200 dpi optical resolution is certainly as high as it gets in wide format scanning. However, 1200 dpi optical is more than can be used to practically scan an A1 / D-size, let alone an A0 / E-size, document in monochrome, let alone color. The resulting file will simply be too BIG to practically use.

200 – 400 dpi optical resolution is typically what most technical drawings are scanned at. This means that a large format scanner with 400 dpi optical resolution is arguably as practical as a 1200 dpi one! Certainly the many scanners offering 600 dpi optical resolution will cover most eventualities when scanning technical documents and maps for archiving, copying, file distribution and raster to vector conversion.

Very high optical resolution like 1200 dpi makes good advertising but provides little or no practical scanning benefits. Even those who have 600 dpi optical resolution will seldom use it. Those with 1200 dpi optical resolution will probably only use it once to prove or disprove the point about file size made here, thereafter never again.

The flipside is that scanners with very low optical resolution, like the old 200 dpi optical resolution Contex Hawk-Eye, are not good enough for raster to vector conversion because they cannot provide optical resolution more than 200 dpi when it is needed. Many of these devices are now coming onto the market as secondhand equipment. Despite what resellers have said in the past about the Hawk-Eye’s suitability for raster to vector conversion, the blunt truth of it is that it is not, never has been and never will be up to the task of creating suitably sharp, well-defined scans from the many drawings that need to be scanned at a resolution of more than 200 dpi.

Interpolated Resolution

Interpolated resolution increases the scanned resolution of an image by calculating (making up!) new data to fill in between the scanned data. All claims for the benefits of interpolated resolution should be dismissed with scorn.

Some companies who should know better claim that high interpolated resolution has benefits for the user. The fact is that interpolated resolution adds no sharpness to an image. It just makes images BIGGER.

As image sharpness is the over-riding requirement for raster to vector conversion, interpolation brings absolutely no benefits to this application. In fact, it is debatable that it offers any benefits anywhere!

Océ claim that their “optional interpolated resolution of up to 9600 dpi” makes the Océ CS4300 series of CCD scanners “ideal for CAD, GIS and other professional users in need of high resolution scans for a wide variety of applications”. This nonsense implies that Océ feel that their genuine 600 dpi optical resolution is not a strong enough selling point in their scanners today (it is).

This poor advice is not Océ’s alone. Other scanner resellers also promote high interpolated resolution in order to sell scanners thought to be too low on optical resolution. We question the quality of the large format scanning advice which you can expect to get from any reseller who misleadingly uses technical specifications to create false impressions.

Place no value on interpolated resolution, aka enhanced and maximum resolution. As a rule, avoid large format scanner resellers who do not offer clear-cut advice on the nature of the resolution they are claiming. If they are trying to confuse you at this basic level, you should not expect objective advice elsewhere.

Scan Speed

Like resolution, scan speed is the subject of much misinformation (see our Scan Speed article on Scanners4CAD).

Claims for scan speed can largely be dismissed because raster to vector conversion is not about how fast the scanner can scan but how quickly you can produce a good quality scanned image. Contex recently introduced a new “productivity” rating which claims to rate productivity by the number of drawings scanned in one hour (700+!). We think this is ridiculous.

When scanning for raster to vector conversion, the interrogation of the scanned image by zooming into it, moving around the image, adjusting and fine-tuning of the correct scan settings to get the best possible quality scan are what are necessary and are what takes time. So, a large format scanner with an A0 / E-size scan speed of, say, 10 seconds, offers no significant benefit over one which takes 20 seconds, especially if its scanning software makes the selection of the correct scanner settings needed to create a good quality scanned image difficult and slow.

When buying a large format scanner for raster to vector conversion the supplied scanning software is a hugely important consideration.

We will look at this in Part III.

By far the biggest barrier to good automatic vectorization results is poor quality scanned images.

With a good quality scanned image, good results are possible from competent vectorization software. With a poor image, the odds are stacked against a good raster to vector conversion result from the start. GIGO! (Garbage In, Garbage Out).

The chief reasons for poor quality scanned images are that too many scanner operators lack proper training and do not understand what scanned image quality looks like. Because manufacturers and resellers claim scanning is easy, inexperienced temporary employees are often delegated with the job of creating scanned images for archiving and any possible future raster to vector conversion. We will look at these issues in a future post.

So, it follows that if you have access to a large format scanner and know what you are doing and are able to scan the drawing with more appropriate settings you will get a better scanned image and better raster to vector conversion results. Unfortunately, too many people wanting to convert scanned drawings to CAD or CNC receive raster images from other sources and do not have the ability to rescan poor images. In such cases, you will need to choose a raster to vector conversion program which has a good set of raster editing tools. However, no amount of raster image editing and tidy-up can replace the benefits of starting the vectorization process with a good and appropriately scanned image. GIGO!

This article is written for anyone looking for advice about buying a large format scanner to use with an automatic raster to vector conversion program like Scan2CAD.

Types of Scanner

There are two basic types of scanner application – technical imaging (drawings, blueprints and maps, etc.) – and graphics (artwork, photographs, etc.). Technical imaging is in monchrome or limited color while graphics is in full color.

Catering for these two basic scanner application areas are two types of large format scanner using different optical imaging technology, either CCD (Charge Coupled Device) or  CIS (Contact Image Sensor). Their differences affect how they capture data, especially fine line sharpness and color.

It is generally agreed by experts that CIS scanners provide sharper results with fine line detail in technical drawings while CCD scanners capture a wider range of colors more accurately, making them the best solution in demanding color graphics applications. This is not a hard and fast distinction but it does allow AEC, CAD and GIS users wanting to vectorize technical images and maps to identify the generally more affordable CIS wide format scanners as their best option.

Scanner Makes

There are three main large format scanner manufacturers – Colortrac, Contex and Graphtec.

Contex is the biggest large format scanner manufacturer and sells its imaging products through distributors and resellers and also via OEMs like GTCO Calcomp, HP, Oce and Vidar who put their names on Contex devices.

Other manufacturers of large format scanners include Image Access, KIP, Ricoh and Xerox. Generally speaking, any scanner supplier not mentioned above is an OEM for one or other product. Several MFP (multi-function peripheral) scan and copy stations OEM Graphtec’s entry-level CIS scanner.

CIS vs CCD

Graphtec was first to introduce a CIS scanner, followed by Colortrac and most recently by Contex. Graphtec do not manufacture CCD scanners. As a result, Graphtec claim that CIS optical imaging technology is suitable for high quality graphics capture.

Colortrac and Contex manufacture both CIS and CCD wide format scanners. Both agree that CCD suits high fidelity, full color graphics capture more than CIS which they again agree is best suited to technical drawings and maps in monochrome and limited color. CIS is suitable for the majority of AEC, CAD and GIS color capture applications.

So, for the purposes of converting scanned technical images and maps into a vector format for editing in CAD, you should first be looking at buying a CIS scanner. However, if you have a requirement to capture high quality graphics images as well, a CCD scanner need not be ruled out. A CCD scanner is more than capable of providing results suitable for automatic raster to vector conversion if properly used.

A CCD scanner is better suited to scanning technical images than a CIS scanner is suited to capturing full color graphics.

Having determined the type of scanner you believe best suits your large format scanning needs, the next thing you need to do is cut a swathe through the manufacturers’ claims for their products. The two areas most clouded in bull and misrepresentation are Resolution and Speed.

We will look at these in Part II.