EXPLANATION:
Large format scanner accuracy and calibration
All large format scanners scanners can produce inaccurate scans if they are not properly maintained and calibrated.
This article describes four areas where problems can occur: Colour uniformity, colour
accuracy, stitching errors and dimensional accuracy. It describes what causes these problems, how
different large format scanner manufacturers go about trying to avoid them and what you need to do to keep your scanner accurate.
Colour uniformity
Colour accuracy
Stitching errors
Dimensional accuracy
Conclusion
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Q&A: ASK AN EXPERT
Q: Can you recommend a scanning bureau?
A: Please click here for a list of scanning bureaus.
Be aware that scan quality varies enormously from one scanning bureau to the next. You may get good quality scans from one bureau and utterly useless scans from another.
In our general experience, the majority of scanning bureaus are more likely to give you a mediocre scan than a top quality scan suitable for archiving and or automatic raster to vector conversion.
Yes, there are good scanning bureaus. The best ones take time and pay attention to the individual detail of each drawing. For them there is no "one size fits all" scanning solution. Because they take greater care to provide you with a quality end product they generally charge more for their personalised services.
Of course, there are some who will charge you as much as they can whatever the quality of their work!
NOTE: Avoid scanning bureaus who quote low (in order to get the work) AND WHO ALSO promise fast turn-around times. They maximise their profit by scanning your job as fast as they can. Too fast in our view! Their priority is to "get it finished ASAP!".
Of course, you can stipulate a reasonable deadline to reduce some of the pressure on them to "bang out the work" but, in our experience, most of these operators will continue to do it as fast as they can because that's the business they're in - low-cost, high volume scanning.
Some scanning bureaus have little or no knowledge of CAD or raster to vector conversion. Few care about the finer intracacies of scanning.
If you are serious about scanning and preserving your legacy data for posterity or for raster to vector conversion, don't accept the first quote you get. Choose those who stress scan quality first and price second.
It is reasonable to expect that a sample scan will show you the quality of work you can expect to get. Unfortunately, this may be the only scan a dodgy operator will put any effort into getting right. Worse, they may also use the settings from this scan as the basis for the rest of your job, the assumption being that all your drawings are the same. They seldom are. On interrogation drawings have many differences between them!
On a big job the worst offenders will use the same pre-determined settings on every scan. They will not interrogate each scan to see if it can be improved in any way by adjusting the settings. They will automatically save each scan with an unhelpful, incrementally updated file name, like "scanarch01", "scanarch02", etc. What they don't see, you get!
Caveat emptor, CAD user!
A good quality scan will generally take longer and cost you more.
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