Scan2CAD raster to vector conversion software

NO BULL:

Phew! Some issues that need cleaning up!

Many large format scanner product descriptions are economic with the truth. When held up to the light of critical scrutiny they display a downside that is not obvious at first.

No Bull - Large Format Scanners

With this column we aim to expose the more confusing and misleading claims to the clear light of day!

In this issue we examine Scan Speed.

As always, large format scanner manufacturers, distributors and resellers are encouraged to contact us with their feedback. In the event of errors and ommissions, these will be promptly corrected once brought to our attention.

Similarly, if you are a large format scanner end-user whose supplier is not giving you the speedy honest answers and technical support you expect, please email us. We will pick up the cudgel on your behalf as quickly as we can.

Scan Speed

All wide format scanner manufacturers need to claim impressively fast scan speeds for their scanners. However, large format scanner manufacturers use different criteria to rate speed. This makes it impossible to compare one quoted speed against another to see which scanner is fastest. Published scan speed figures are fairly meaningless in any comparison. However, it is important to manufacturers that they look FAST!!!!

One of the first things a newcomer to scanners must understand about scan speed is that the lower the resolution, the faster a drawing will be scanned. As a result, some manufacturers measure scan speed at 200 dpi because this creates a useful impression of speed. They don't use the faster 100 dpi because this is too low resolution to be impressive. But nor do they use 400 dpi because the scans would appear to be too slow.

Enter Contex's 400 dpi turbo mode.

Contex Turbo Mode

Contex HD3650

Contex HD 3650 rated at 400 dpi turbo

Contex publish their scan speeds measured at "400 dpi turbo".

Few understand exactly what Contex mean by "turbo". As a prefix "turbo" generally implies speed and power, as in "turbo-charged performance" - like a racing car!

In scanner speak, it is a clever compromise that allows Contex to claim a higher resolution - 400 dpi turbo - while still generating impressively fast scan speeds. Here's how it works!

In 400 dpi turbo mode, the scanner scans at 400 dpi optical along the width of a drawing and at 200 dpi optical along its length. By scanning the length at 200 dpi, the scanner is able to scan faster than it would be able to at 400 dpi.

After scanning, the 200 dpi is automatically interpolated back to 400 dpi (in other words, the scanner "invents" extra data to bulk the resolution back up to 400 dpi). This is faster than scanning the length at true 400 dpi optical but results in a loss of quality as 400 dpi interpolated is never as sharp as 400 dpi optical.

Of course, nobody mentions the poorer quality result in "turbo" mode. The unstated emphasis is all on speed! Turbo speed!

Contex's OEMs - GTCO Calcomp, HP, Océ and Vidar

Most of those who badge Contex scanners with their brand names - GTCO Calcomp, HP, Océ and Vidar - use "400 dpi turbo" to rate scan speed. However, the web site of GTCO Calcomp quotes Contex's scan speeds with no qualifying explanation whatsoever.

HP is the only Contex OEM to differ, quoting scan speeds measured "at 200 dpi". The UK HP brochure further qualifies scan speeds as having been measured using an "A1 drawing". Is HP using a narrower scan width to make its scanners appear faster? See Colortrac Small Print, below!

Graphtec HD Scan Speeds

Graphtec IS210

Graphtec's entry-level mono IS210

Another company that publishes speeds with compromised scan quality is Graphtec.

Graphtec are using an HD - High Definition - tag to describe their wide format scanning products, the CSX300 / IS210 / CS510 / CS610 models. This conveniently hides the fact that all are only capable of their advertised 600 dpi optical resolution ("high definition") in the very slowest scanning mode.

Unsurprisingly, Graphtec like to claim their scanners are fast! Here's how they do it.

High Quality, Normal and High Speed modes

Graphtec CSX300 scanners and IS/CS Pro models have three scanning modes - High Quality, Normal and High Speed.

High Quality mode scans at 600 dpi optical resolution. It is slow but - as the name suggests - gives high quality results.
Normal mode scans faster but resolution is compromised in the X direction.
High Speed mode scans fastest of all but its resolution is compromised in both the X and the Y directions.

In their product literature, Graphtec publish scan speeds at an impressive 400 dpi resolution - but they only publish them for Normal mode and High Speed mode. As with Contex's turbo mode, nobody mentions the poorer quality result. The emphasis is on speed! High speed!

No scan speeds are published for High Quality mode. Presumably, Graphtec consider them TOO SLOW!!

Base and Pro models

Graphtec supply scanners in both Base and Pro models. All Graphtec Base models have only one mode - Normal. This has the following implications:

  • Resolution

    Graphtec scanners only scan at true 600 dpi when used in High Quality mode.

    Graphtec Base models do not have a High Quality mode, therefore they cannot scan at 600 dpi.

    Any description of a Graphtec Base model scanner as either being High Definition or a 600 dpi optical device is therefore misleading.

  • Speed

    Graphtec's literature implies that Graphtec Pro models are faster than Graphtec Base models.

    In fact, the scan speed of Graphtec Pro and Base models is the same in Normal mode.

    The extra speed of the Pro models is achieved using High Speed mode - with a reduction in scan quality - and so is useless unless you are prepared to accept the quality compromise.

Colortrac Small Print

While both Contex and Graphtec use quality compromising modes to increase their published scan speeds, both measure their speeds using full size documents.

Colortrac Cx 40

Colortrac's SmartLF Cx 40

Colortrac publish scan speeds at 200 dpi with no special modes. However a note in the small print at the bottom of the technical spec sheets for Colortrac SmartLF Cx 40 and Gx 42 scanners states that "quoted top speeds decrease for originals wider than 24in and are not guaranteed for all media types". This indicates that Colortrac's published speeds are measured using a 24" (A1 / D-size) document that does not cover the full scan width of the 40" Cx 40 and 42" Gx 42. Why does this matter?

When a scanner scans, the scanned information is transmitted to the receiving PC down the USB2 connection and stored. The USB2 connection is a bottleneck. It can only transmit and store a given amount of information at a given speed. This means that the more information the scanner generates, the slower it must scan in order to get the information down the USB2 connection. If it scans too fast, it will need to pause while already scanned information is transmitted.

The wider the document being scanned, the more information is sent down the USB2 connection. This means that the scanner will potentially scan slower when a wider document is being scanned. By publishing speeds measured on an A1 / D-size document rather than an A0 / E-size one, Colortrac is able to publish faster scan speeds.

It's interesting to note that the two fastest scanners we have tested to date (see below) use a Gigabit Ethernet connection which allows a far greater volume of information to be transmitted (Image Access) and a modified USB2 interface that allows faster data transfer (Contex SD series with "xDTR").

Conclusion

Take manufacturers' published scan speeds with a pinch of salt!

When reading published scan speeds, take note of the resolution the speeds were measured at and whether there are any qualifying phrases, notes or small print. If there are, the scanner's real speed is probably being obfuscated.

The problem is that often there are no notes! For example, Contex OEM GTCO Calcomp quotes Contex's turbo mode speeds with no qualifying explanation whatsoever. Then there is Graphtec's use of the word "normal". Normal implies ... normal. You don't expect normal to be quality compromised.

Finally ... remember that the speed you will be able to scan at depends on a variety of factors including the efficiency of the scanning software you are using, the condition of the drawings you are scanning, your intended end use and the specs of the PC you are scanning to. Raw scan speed is only one part of the scanner speed equation.

And Finally, for the record ...

Scanners4CAD have measured the time it takes to scan the same A0 (E-size) sheet at 200 and 400 dpi on several different scanner models without using quality compromising modes.

The time shown is the time it took from the clicking of the "scan" button to the scanner's software becoming available again after the scan.

All times were measured on a 3.4GHz Pentium 4 with 1Gb RAM with the exception of the Contex HD4230i, which was tested on a 3.2GHz Pentium 4 with 1Gb RAM.

  Image Access WideTEK 36 Contex SD4490 (1) Colortrac SmartLF Ci 40e (2) Graphtec CSX300 (3) Colortrac Cx 40e Contex HD4230i Graphtec CS600 (3)(4)
Black and white
200 dpi 7 sec 7 sec 13 sec 9 sec 13 sec 9 sec 33 sec
400 dpi 17 sec 12 sec 29 sec 17 sec 24 sec 10 sec 38 sec
Greyscale
200 dpi 7 sec 7 sec 10 sec 10 sec 13 sec 12 sec 32 sec
400 dpi 17 sec 20 sec 22 sec 21 sec 24 sec 27 sec 33 sec
24-bit Colour
200 dpi 7 sec 19 sec 19 sec 23 sec 36 sec 35 sec 40 sec
400 dpi 17 sec 63 sec 46 sec 68 sec 80 sec 105 sec 60 sec


(1) The specs of the PC used to time the scans are below Contex's recommended specs of a 1.66GHz Dual Core Processor, 2GB RAM, a 7200rpm SATA hard drive with 5GB free space and a high speed USB 2.0 interface.
(2) Timed using ScanWorks software which scans in greyscale even when you do a black and white scan. This confers a productivity benefit onto the scanner by allowing scan settings to be modified after scanning without a need to rescan.
(3) Timed using High Quality mode.
(4) Now replaced by the Graphtec CS610 and updated Scanning Master software which may scan faster.