Large format scanning has become instrumental for many AEC (architectural, engineering, & construction) companies.
Powerful CAD programs and other software applications, such as Bluebeam Revu, are changing the way construction documents are handled, viewed, marked up, and shared. But, what about the vast number of archived drawings stored in flat files?
Many business leaders are opting to get a large format scanner to digitize those files, but when considering a purchase, there can be some confusion on selecting the right scanner for large documents.
There are two primary types of wide-format scanning technologies to consider. Both have their merits, but it really is a matter of application regarding which process it right for your situation.
Read on to learn the difference between the two to determine which one is best suited for you - CCD vs CIS scanner technologies.
CCD Technology Scanner
CCD stands for Charged Coupled Device. In essence, this is the same type of imaging sensor found inside a legacy digital camera. CCD uses an actual lens to reduce the full image onto the imaging sensor.
This method is great for capturing very high resolution details along with widened color space.
It is because of the fine detail in the CCD type scanner that makes it the scanner of choice for higher resolutions graphics and artistic applications. Still it is common to see CCD types of large format scanners that are used for AEC or technical scans as well.
Another benefit to CCD scanning is a greater depth of field. This is helpful if you plan to scan many folded sheets. With CCD technology, fold lines can be tweaked a bit through the scanning software so that they don’t image as much in the scanned file. CCD scanners also have the ability to scan "mounted" or thick originals.
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Advantages of CCD Scanners
- High signal/noise ratio due to florescent lamp light source
- Relatively insensitive to focus depth due to cameras with apochromatic lenses
Disadvantages of CCD Scanners
- Higher equipment cost
- More complex and fragile technology
- Larger form factor than CIS types
- Typically require digital stitching of multiple image fields
- Lower optical resolutions
- Lens distortion can sometimes be a factor
What about CMOS Sensors?
Sometimes there is some confusion regarding CDD sensors and CMOS sensors, since they are both based on an apochromatic lens focusing light on capturing sensor.
In a lot of ways CMOS (complementary metal-oxide semiconductor) has become more commonplace regarding the status quo. This is mainly due to their use in personal digital cameras.
If you look at the specs of just about any point-and-shoot or digital SLR camera, it is usually a CMOS device under the hood. Although both sensors (CCD and CMOS) start at the same point - converting light into electrons, but there are some differences.
Reasons Why CCD Is Better For Large Document Scanning
- CCD sensors create high-quality, low-noise images.
- CMOS typically produce more noise.
- The light sensitivity of CMOS sensors tends to be lower.
- CMOS sensors use very little power. This is why they are great choices for hand-held cameras. CCDs on the other hand, require much more power, but they produce great images. Since CCD-based large-format scanners are stationary devices, the power trade-off is a moot point.
Overall, CCDs traditionally perform better in high-quality image environments. So, scanner manufacturers have stood by this technology rather that transitioning to a CMOS sensor.
"Both CIS and CCD technologies have there merits, but it really is a matter of application regarding which process it right for your situation. "
CIS Technology Scanner
Contact Imaging Sensor (CIS) is the other type of scanning technology. Instead of using a standard lens to reduce the original image onto the sensor, CIS technology incorporates many fiber optic lenses to transfer the original image information to an array of sensors.
CIS technology is less expensive than the traditional CCD models, but there can be some trade-offs regarding image quality, especially when it comes to scanning aerial photos or maps.
Since there are no cameras to calibrate and the sensors are controlled by software, there is much less maintenance with a CIS -based system.
But, because of the poor depth of field of the optics, fold line and wrinkles will image with CIS. Also, there is a reduction of color space information with CIS.
Unless you want to capture mainly primary colors, CIS could leave you wanting a little more.
But, keep in mind, although the physical CIS technology has some limitations, many manufacturers have overcome this by deploying sophisticated software that compensates for the CIS shortcomings.
A great example of this is the Canon Color Image Logic employed by all Canon/Océ wide format systems. Likewise, other manufactures have followed suit and release their own “clean up” software tools.
So, most of the time, there can be a good case made for CIS versions, especially when budgets are constrained. CIS scanners have largely become the scanner technology of choice for those needing blueprint scanners.
Advantages of CIS Scanners
- Less Cost
- High reliability
- More compact
- No stitching required
- Higher optical resolution
- No lens distortion
Disadvantages of CIS Scanners
- Sensitive to focus depth
- Lower signal/noise ratio due to LED light source
CCD vs CIS Takeaway
If you work with CAD/GIS drawings and you want to scan them into a digital format - CIS is worthy of your consideration. It certainly is the more cost effective solution and new, powerful software applications have narrowed the difference between CCD and CIS.
But, if your quality requirements are more demanding, such as with photos or fine art, you should really be looking at a CCD scanner. It will give you the absolute best image quality, hands down. Sure, it will be much more of an initial investment, but it will be well worth it in the end.
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Editor’s note: This post was originally published in 2011 and has been updated for accuracy and comprehensiveness.