Scan2CAD raster to vector conversion software

Large format scanning hints and tips

Old Al's Large Format Scanning Hints and Tips Page

by Alan Darbyshire

Alan is an independent consultant with wide experience in all aspects of CAD hardware and software going back as far as Benson pen plotters. Alan's cheerful greeting welcomed many British CAD users to CADlogic's booth at UK construction industry exhibitions. His long association with CADlogic ended a few years ago when he started his own CAD services business. He now provides training on AutoCAD and AutoCAD architectural add-ons, offers a "first quality" drafting service that recreates old drawings as new (aka "CAD perfect"), as well as a scanning and conversion service using a Colortrac SmartLF A0 scanner and Scan2CAD raster to vector conversion software. He currently lives in the scenic Peak District of Derbyshire in England.

aldarbyshire@btconnect.com
http://www.alandarbyshire.co.uk

Outline of Mono Scanning - in a Perfect World!

If you were to take a "perfect" 100% top quality technical drawing with no torn edges, no holes, no splits, no curled portions and push it through the average wide format scanner at its average setting, then you would most probably get a reasonably decent quality scanned image.

However, we do not live in that perfect world!

THE REAL WORLD - WHY’S AND WHERE’S

Technical drawings and documents once completed have to be stored. During their time in storage all sorts of things can happen to them.

They get torn (and possibly sometimes repaired with sticky tape).
They get curled at the edges, the corners get folded over.
They get creased ...sometimes quite badly so.
They get dirty for a variety of reasons - have cups placed on them, fly ...., etc.
They get dusty.
They get faded with time.
They get damp and stretch; they get dry and shrink.
They get copied, the original gets lost ....some are copies of old blueprints or dyelines.
They get fixed to ‘hangers’ and placed in upright drawing chests.
They are left rolled-up for years and years.
They are folded and stained in the creases.
They are on paper, film, linen, tracing, vellum, mylar, back of fag packet!

Drawings in these conditions are confronted by everyone who wishes to scan drawings from their "average" drawing / design office. All these problems can be overcome with careful scanning.

Here are my Hints and Tips based on my experience of scanning drawings in these conditions and going through that learning curve.

GETTING THE PAPER INTO AND THROUGH THE SCANNER

Sounds really easy …feed in …scan …take out!

However, this is generally not the case. As per the list above drawings in the real world get torn, creased, curled, etc. These cause the scanner operator problems when feeding the drawing through the scanner.

A few simple rules that will help:-

Problem …Pressure on the drawing
Drawings that snag or get stuck often do so because of incorrect pressure on the paper. Most wide format scanners allow pressure adjustment to suit the media you are trying to scan.

Generally the lowest setting will get the ‘average’ drawing through without any problems.

Note: If your drawings start to curl as they are fed through it is normally a sign of too much pressure on the rollers. This normally occurs if the media is very thin or flimsy. The solution is to adjust the pressure to suit your media.

Problem ...Torn or curled leading edges
If a drawing is badly torn or curled on the leading edge you want to feed it through on i.e. the edge that gets the drawing into the "correct" orientation when viewed on screen, simply feed it through the scanner on another edge that is in better condition, then rotate the drawing using the scanning software afterwards. This may take a bit longer but it saves fiddling around trying to unjam snagged or stuck drawings.

Problem ...Drawing corners in poor condition
If all the corners of the drawing are in very poor condition i.e. torn or dog-eared, and you struggle to feed them in in any direction, simply snip the corners off at 45 degrees. Try to cut off as little as possible as this can cause problems with feeding and finding the feed sensor. This applies to the front feed sensor and rear "Paper End / Finish" sensor.

Note: If you do cut too much off, you can simply tape another piece of A4 paper to the back of the drawing to ‘make-up’ the corner.

Problem ... Taping up drawings
Badly torn drawings will benefit from being taped-up, so take some time to repair them before you scan. Otherwise you can end up tearing the drawing even more if it gets caught up while being scanned. If you know a drawing is in poor condition, please pay attention to the drawing as it is being scanned. If it snags …press the STOP Button on your scanner immediately and Rewind or remove the drawing. Repair and re-scan it.

Problem ...Drawing feeding in poorly from the start
If a drawing is fed in and it is not scanned in straight, you will either have to rescan it or do a Rotate (deskew) on it to straighten up again. Rotate is usually carried out in your scanning software. It is sometimes very difficult to get a drawing that is in poor condition to feed in straight, so you will have to accept the fact that you must either rescan or deskew afterwards.

Note: It is recommended that your scanner includes software that allows you to post-process a scan i.e. manipulate the image after scanning. If it does not you will be forced to adjust your software settings and rescan once more – this is VERY time consuming. Using the Rotate command in your software is the better option.

Problem ...Drawing Hangers
These may sometimes have to be cut off. However, I have found that this is rarely necessary. Even thick card hangers will go through with no problem, even if you use them as the feeding edge of the drawing, provided that you have the correct pressure set. Again minimum settings are recommended for 99% of "general" work.

Problem ...None of the above solves a drawing feed problem
If you find that you are still struggling to get a drawing to feed through the scanner, you may have to trim the edge completely to get a straight edge to feed with. Alternatively you can purchase a Large Format straight edge to do this (about £100) or just use scissors. I personally use the scissors. They're cheaper and easier to store, plus need less room to use!

Problem ...Transparent Films
These can cause you a problem on many scanners when using Auto-Size because the scanner can’t detect the edge of the film, particularly if the drawing has no "outline border" (title block) drawn on the sheet. You have two solutions. Either set the paper size to greater than A1 / A0, etc., or draw some lines at the edge of the feeding edge in felt pen for the scanner to "sense".

NAMING YOUR SCAN FILES AND SORTING DIRECTORIES
(Applies to CAD Drawings too!)

The biggest problem with using any numbering systems for your drawings is that without the numbers you have no clue as to what a particular drawing is and who or what or where it is associated to.

Even if you do use a numbering system, it is sometimes better to incorporate that number into the drawing name along with "other" relevant information so that future users of the scanned file can easily find and view / print the drawing.

The method I have introduced to many companies is a logical and easy system and can be searched for inside Windows Explorer. The system uses the local name of the item. For example, if it were an architectural detail drawing it could be:

VICAR-RD-IND-UNITS-RTFRD-EX-PL+EL-A12345678-A1
Vicar Road Industrial Units: Retford: Existing: Plan plus Elevation – Drg No: A12345678 on A1 Size Sheet

Note: Producing a common list of abbreviations for users is worthwhile as these can then become "standards" in your file naming conventions. Such a list could have many abbreviations. Here are some examples:

Common WordAbbreviation
ArchitectsARCHS
BungalowBUNG
CAD FileDWG
CouncilCNCL
DrawingDRG
ExistingEX
ElevationEL
HouseHSE
Planning PermissionPLANP
Proposed PR
SectionSECTN
Light (scan)LT
Dark (scan)DK

Stick your list on a board and keep it near your scanner PC for quick referencing.

If you then store these via Customer Name / Area in different Directories, then they can be very easily found by anyone with just some basic knowledge of how to use Windows Explorer as a search tool.

One benefit of this method is that it saves you from using a complex, customised DOM (Drawing Office Management) system to front the drawings / scans. It also saves you the added expense of purchasing a copy for each PC that needs to search for drawings.

Note: The Field to enter this information in is quite small in many scanning software programs. As a result, this may not be ideal if your software restricts you to a small description field. Keep it easy ... be sensible and name your scans correctly and you will be able to use standard Windows search facilities to find your scans.

FORMATS USED FOR SCANNED IMAGES

Monochrome scanned Images are normally saved as .TIF (Tagged Image Format) files, usually as a compressed TIF (Group 4) file.

Images can also be stored as PCX, PNG, PDF and WMF. These formats are useful and mainly used for colour images. In particular, PDF has become a good "standard" for non CAD / design users to exchange information in and be able to view and plot drawings. PNG is a relatively new compressed colour and monochrome file format. WMF and PCX are Windows formats, again mainly for colour work. JPG and JPEG use compression that loses data so are not recommended.

As a rule, for all monochrome scanning TIFG4 is the format to use.

PRINTING AND VIEWING SCANNED IMAGES

There are many viewing solutions available from free to a few hundred pounds. Before you invest in any of these programs you should look at 'what you want to do' with the scanned images.

You will find that there are lots of View / Print programs available on the web, so look for the best one to suit your needs. Download a "Trial copy" and have a go.

WARNING! MOST IMPORTANT - MAKE REGULAR BACK-UPS

Always back-up your scanning work every day or after each job. There is nothing worse than having to rescan a massive pile of drawings again, partcularly ones with the problems outlined here. MAKE REGULAR BACK-UPS.

You have been warned! TWICE!!

Scanning – What to look for in a scanned image

I started off in the scanning business as a complete novice. I was starting my own CAD drafting and training business and I wanted to offer scanning as an extra service to my customers. As I needed the work I needed to get up to speed quickly.

Buying a second-hand scanner
Unfortunately, there were no helpful web sites like Scanners4CAD at that time so I trawled about the net but having only a limited budget I ended up buying an old Océ A0 mono device that was still running under Win 3.11 with a SCSI interface!!

Now in fairness this Océ scanner proved a great workhorse, plus it had the benefit of not being too expensive. Most new scanners were £8 to £10k plus at the time. I bought the Océ for £1000 and sold it for the same a year later. The Océ must have been designed by Isombard Kingdom Brunel, as you could hardly lift it. I am sure that if my office roof caved in, the Océ would still have been standing defiantly amongst the rubble!!!

This experience taught me a lot about scanning as I basically had to learn as I went along. The Océ did earn me money which was was the reason for purchasing it in the first place. Since then I have purchased a Colortrac 4080 series A0 scanner and have used that for over a year-and-a-half now. In the UK Colortrac were the ones who forced the price of large format scanners down, much to the chagrin of their expensive competitors.

What do you ‘really’ want to do scan-wise?
Many CAD users buy a scanner for archive purposes, scan-to-copy, scan-to-print and raster to vector conversion (scan and convert into DXF for CAD to save re-drafting). Others buy scanners for colour graphics work which generally requires a much more powerful colour scanner than CAD users need.

Whatever you do make sure you are as future-proofed as you can afford to be.

If you don’t need to scan colour pictures or drawings then you can save a little by buying a mono (B/W) only device. However, if you are in business to scan a customer's drawings, then you will always need to have colour capability (just in case). The majority of my work is mono scanning but the odd colour scan is always required.

If you need to scan direct to a printer, make sure that the system will work with your particular scanner and or printer. Some systems use dedicated drivers to scan direct. HP printers are one of the most popular supported devices. If you buy one of these you are unlikely to go wrong. Similarly Canon printers.

Is your PC powerful enough?
Make sure you have a powerful PC. You may think that you have got a very powerful PC but I found that even with USB 2.0 - you cannot run a modern scanner with USB 1.1, it is too slow - and a fastish processor, scans could drop or the system would hang and this is always very frustrating.

I had a laptop that was greater than the specification required by the scanner manufacturer. It wasn't until I purchased a brand new laptop that I resolved a lot of the annoying issues that occurred when batch-process scanning. So check with whoever is selling you the scanner, the reseller in the first instance and their supplier in the second if the reseller is unhelpful or unwilling. Ask to speak to a customer who is using one of their scanners, if possible. This might help you learn of any "issues" before you make the purchase.

Post-processing of scans
One thing the old Océ did not have was the ability to post-process the scanned image. In other words, it did not allow you to manipulate – rotate, despeckle – the image after it was scanned. Most modern scanning software will do this. It is very important that your scanning software has good post-processing tools. They will save you considerable time re-scanning if the scan is not good enough. Post-scan clean-up tools are a 100% requirement.

Always, always check your scans
I am always very conscious of the fact that I have to take care with my scanning, particularly if, say, three years later my client wants to be able to get information from a drawing that has been scanned for archive purposes.

(Editor's Note: There exist in the world today millions of drawings which have been poorly scanned on very expensive scanners. Once archived they are not fit for anything but viewing as a facsimile copy. The poor scan quality of these drawings is not good enough to convert with raster to vector converters like Scan2CAD. Worse, the original drawings are often destroyed after scanning so there is no chance of doing it again).

I always check a scan straight away to see if it is readable. This is because you can sometimes get a scanned drawing where part of the image is dark and another part is quite faint.

You will not always be able to get everything readable in a single scan. I therefore do a second scan on a different setting. I save the second scan with a –2 after the filename, sometimes with an –lt (for lighter scan) or –dk (for darker scan). This way, between the two scans, the customer should be able to retreive any vital information later by which time perhaps the originals have been shredded!

Save the file in a compact file format. I generally scan to TIF G4 which is an ideal format for mono work.

Many scanner manufacturers are also offering the ability to scan direct to PDF (Adobe Acrobat format). A lot of my clients ask for this. Make sure that you include the ability to scan-to-PDF in your choice of scanner software. The growing popularity of PDF makes it an important feature to offer to your customers.

Always, always check your scans
This may seem like a repeat of the above but I have also found that I can scan a file and save it and when I look it appears correct, yet when I check the directory the scan is in it has ZERO bytes!!! Yikes!!!

I now check the directory as I scan to ensure that scans are actually being written correctly, plus I check the hard drive with fast viewing software. I use Irfanview for this – it’s free off the web.

http://www.irfanview.com/

With Irfanview I can quickly skip through the files to check it’s all as I expect. This is, of course, more work but you don’t want someone coming to you in a few months saying that a very critical drawing among those that you scanned for them is blank, do you?

Disclaimer

While every effort has gone into ensuring that all the information herein is correct, if you do find any errors, please report them to me and I will get them rectified.

Alan Darbyshire
Tel: 01457-858221
Mob: 07798-611792
aldarbyshire@btconnect.com
http://www.alandarbyshire.co.uk

© Alan Darbyshire 2006.