Scanning uncovered

539 0

Steve Hannath of Softcover looks beyond the marketing hype and tells you all you need to know when buying a wide format scanner for CAD.

Graphtec SP200W.

CAD users wanting to buy a standalone wide format scanner for archiving, printing or raster to vector conversion of technical drawings and maps face a growing array of choices and confusing claims. There are two main types of scanner technology: CCD (charged couple device) and CIS (contact image sensor).

” There are three types of resolution – optical, interpolated and real – but optical resolution is the only resolution that means anything. It is the highest resolution that the scanner is physically capable of scanning at. “

Vested interests on either side have white papers on ýCCD versus CIS¯ explaining the superiority of their technology over the other. Depending on whose article you read the other technology is utterly unsuited to your requirements. Nothing is further from the truth. CCD technology has been in production longest and has the greatest number of users worldwide. CIS technology is newer, more affordable, growing in popularity and, despite what its CCD critics say, capable of good results, especially in monochrome.

CCD scanners are generally agreed to have a wider colour gamut, (ability to scan a wider range of colours), a higher dynamic range, (ability to capture smooth gradations of tone), and better resolving power, (ability to distinguish between closely spaced lines, etc). Generally, this makes CCD better suited to demanding professional reprographics work. Both technologies are suitable for scanning monochrome or colour technical drawings but increasingly CIS scanners are more likely to do it at a price the average CAD user can justify.

Manufacturers

There are many scanner suppliers but only a few scanner manufacturers. Contex (Denmark) and Graphtec (Japan) are the two major scanner manufacturers. Contex sells only CCD scanners while Graphtec sells only CIS models. Both are sold under other brand names: Calcomp, HP, Oce, Vidar (Contex) and KIP (Graphtec).

Colortrac (UK) is the only manufacturer to produce both CCD and CIS scanners. Colortrac recognise ýthe individual merits of CIS and CCD sensor technology and …. provide products optimised for technical documents or graphic arts imaging applications¯. Colortrac CCD scanners are also sold under the Paradigm Imaging brand.

Image Access (Germany) offer the WideTEK 36, an OS independent, networked CCD scanner that includes a built-in PC. It is branded by Bowe Bell + Howell in the USA. Shapemakers (Australia) offer the Deskan, another unique device, a CCD scanner that scans an A0 drawing in seven A4 strips which are automatically stitched together.

Advertisement
Advertisement

{mospagebreak}

Colortrac SmartLF cx40 with PC and Screen

Models

Contex, Colortrac and Graphtec all offer different scanner models at different prices. Within any manufacturerÝs range, models are largely differentiated on the basis of one of more of the following: colour capability (black and white only or colour), scan width, the thickness of the media you can scan, scan speed and interpolated resolution.

Specifications

Some manufacturers manipulate product descriptions and system specifications in order to gain a competitive edge.

Scan speed: No standard benchmark test exists for scan speed. As most manufacturers rate scan speed differently any straightforward comparison of their claims will be misleading.

The lower the resolution the faster the scan, so the lower the resolution used for the published scan speed, the faster the scanner appears. Colortrac publishes scan speed at 200 dpi. Contex publishes speed at ý400 dpi Turbo¯ which is effectively 200 dpi. Graphtec publishes scan speed at 400 dpi and Image Access and Shapemakers publish scan speed at various resolutions.

Also, scan speed is influenced by the host PC specifications, especially when scanning at higher resolutions and in colour. As a rule, scanners scan faster than PCs can capture the data. An expensive fast colour scanner can be as slow as an entry-level slow colour scanner for all practical purposes.

Note that the speed of the scanner is only a small part of the overall process of scanning technical drawings.

Resolution: There are three types of resolution – optical, interpolated (often referred to as ýenhanced¯ or ýextended¯) and ýreal¯.

Optical resolution is the only resolution that means anything. It is the highest resolution that the scanner is physically capable of scanning at. Most technical drawings require to be scanned between 200 and 400 dpi optical. Most scanners today are 600 dpi optical devices with the exception of Contex scanners which are largely 508 dpi.

Interpolated resolution should be ignored as it adds no detail to a scan but adds enormously to the file size. Yet both Graphtec and Contex use it as a justification for their higher priced Plus models.

Contex recently replaced optical resolution as a measure of resolution with a value of their own choosing which they call ýreal¯ resolution. Contex argues that its ýreal¯ resolution better indicates the overall scanned image quality that their products offer. Thus you will see Contex scanners with 508 dpi optical resolution described as having ý600 dpi resolution¯.

Some Colortrac ads describe SmartLF Gx scanners as having 1,200 dpi optical resolution. In fact SmartLF Gx scanners scan at 1,200 x 600 dpi optical and save at 600 x 600 dpi, so they are more accurately described as having 600 dpi optical resolution.

{mospagebreak}

Image Stitching: All scanners except those that use one camera, like the Contex Hawk-Eye, scan in strips and ýstitch¯ them together. Despite manufacturersÝ claims, all potentially have stitching issues and need to be calibrated from time-to-time to overcome this problem. We have seen stitching errors in scans made by scanners from all the major manufacturers – Colortrac, Contex, Graphtec and Image Access.

48-bit colour capture: Contex and Colortrac both offer 48-bit colour capture. This means that the scanner scans in over 281 trillion colours and then chooses ýthe best¯ 16.7 million colours (24-bit colour), which it saves. Image Access offers 36-bit capture (68.7 billion colours) and Graphtec 24-bit colour capture.

36-bit colour capture captures the entire range of colours that can be represented on the best quality scannable media (film transparency). Therefore the extra colours that can be captured by 48-bit capture offer no extra detail. It especially offers nothing to CAD users scanning monochrome technical drawings or drawings with only a few colours.

Scanning software

TodayÝs wide format scanners capture technical drawings with much the same scan quality. Paying more does not bring further benefits for most technical drawings. Any practical difference is in the scanning software. Most scanners have TWAIN support which means they can be used with any software that supports TWAIN, such as Photoshop and Scan2CAD raster to vector conversion software. In addition to TWAIN support, scanners are usually supplied with free and/or paid-for proprietary software. There are three major productivity features to look for.

” Anyone with dirty and ýdifficult¯ technical drawings is recommended to evaluate the scanning software and its overall usability with as much enthusiasm as you examine the hardware. “

The ability to change the scan settings AFTER scanning the image. This means that the correct scan settings can be established without having to rescan all or part of the drawing.

The ability to VIEW the changes you make to the scan settings in REAL TIME as you make them. This means that you donÝt blindly set scanning values without knowing the effects they will have. It avoids endless experimentation.

A good range of zooming and panning tools so that it is quick and easy to view the image in detail to make sure it has been scanned to your satisfaction.

In addition, for cleaning dirty technical drawings it is vital that you have practical simple and adaptive thresholding functions. Most scanning software offers thresholding but in some the implementation is so poor it renders the function awkward or useless. Finally, there are many other features like auto paper sizing, image rotation, crop and deskew that will add to your productivity.

If you are intending to print your scans, you will probably want to use the printer you already have. Some software supplied with scanners is restricted in the printers it supports. You need to ensure that your printer is supported. Printing features to look for include the ability to print to scale, reduce, enlarge and print multiple copies. Some print software supplied with scanners includes colour matching to ensure that colours that are printed closely match colours on the original scanned document. This is unlikely to be of significance to CAD users scanning technical documents.

If you are going to do a lot of printing, consider a RIP (raster image processor). A RIP is a program that makes printing faster, more efficient and gives you more control over the printing process.

Networking

Contex has a proprietary software networking solution for almost all of its scanners. Colortrac and Graphtec do not.

Most scanners are required to run from a dedicated host PC but can be networked using WIDEsystemNET (Contex) or SCP EasyScan software (Colortrac and Graphtec). Networking requires scanning software and/or drivers to be installed on the dedicated host PC and on every workstation.

New generation network scanners, like the Image Access WideTEK 36 with its built-in PC, make the need for a host PC redundant and can be run directly from internet browsers across a network.

Support

Some companies offer an on-site warranty. This tells us they believe in their product. Others offer return to factory (RTF) warranties that can be upgraded at extra cost to on-site or swap-out. RTF warranties require the scanner to be returned in the original large box which must therefore be stored, possibly an unwelcome encumbrance.

Conclusion

CIS scanners are suitable for scanning most monochrome or colour technical drawings to file, print or copy. CCD scanners are recommended to those for whom fine details and precise colour accuracy are main requirements.

For most CAD users a 36¯, 400 dpi optical resolution, 24-bit colour scanner is suitable for scanning large format technical drawings. Happily, large format scanners today are comfortably over-specified for the needs of CAD users. However, anyone with dirty and ýdifficult¯ technical drawings is recommended to evaluate the scanning software and its overall usability with as much enthusiasm as you examine the hardware. Increasingly, it is scanning software that makes the difference in terms of productivity and the quality of results.

 

Advertisement

Leave a comment