How to choose a large format scanner

The following points are important for purchasing a scanner

1. Key Technologies

The imaging system (Imaging System) is the core of the large format scanner, including image acquisition (Image Acquisition) and illumination system (Illumination). According to different image color methods, the large format scanners currently on the market mainly use CIS (contact image sensor) and CCD (optical coupling device) technologies.

Scanners with CIS technology have low cost, small size, and sharp and sharp images. However, because the color space of the sensor is relatively small, scanning color images is not very full. The scanner of CIS technology is mainly suitable for the scanning of technical documents (Technical Documents) such as CAD drawings, sketches, GIS maps, aerial photographs, clothing drawings, newspapers, office documents, etc. If you only need black and white documents to be digitized, then it is recommended that you buy A black and white scanner is sufficient. If you still have some color line drawings or color images, but the color requirements are not high, then the CIS color scanner is enough.

Scanners with CCD technology are more expensive and bulky. The color gamut of their sensors is wider, the continuity of scanning color images and the shadow and highlight details are more soft and full. The CCD technology scanner has the widest applicability and can scan various types of documents well. However, due to its relatively expensive price, it is especially suitable for users who have high requirements for image accuracy. It is used for the scanning of art image documents, such as GIS maps, aerial photographs, art works, photos, posters, sketches, etc.

2. Paper feed mechanism (Paper Feed)

Digitization of large-format documents requires the documents to be digitized by the scanner feed mechanism driven by the scanner imaging system, so be sure to test the paper adaptability (Paper adaptive) of the scanner according to the type of documents in the unit, such as some scanners. Not suitable for scanning thin newspaper documents, because of the design of the paper feed mechanism, it often jams or even damages the original. Another example is that some scanners are not suitable for scanning curled and wrinkled documents. Paper is often jammed or the shadow of the scanned image crease cannot be removed due to the paper feed mechanism. The effect is very poor. At present, large-format scanners using single-roller paper conveying system (ASRPT) or all-wheel drive dynamic paper conveying system (APT), combined with dual LED lighting systems, can solve the problem of paper jams and crease shadows. , And can better improve the accuracy of the scanned image.

Therefore, before purchasing a large-format scanner, it is best to bring various typical documents of the unit (it is best to be useless, and the paper jam is not afraid of damage) to the dealer who can provide a prototype demonstration for personal testing and experience. For thin or curled documents, try to scan as many times as possible to see if there is paper jam and the image effect at the crease. The paper feed mechanism has the greatest impact on the image accuracy of the scanner. If you require a higher image accuracy, such as GIS users, it is recommended to go to the site to be actually tested by professionals. The accuracy indicators promoted by manufacturers often have a certain amount of moisture in them.

3. Correctly understand the main technical indicators (Specifications)

Don't be confused by the technical indicators called by the factory's trademark, only by correctly understanding the true meaning can you better choose the large-format scanner that suits you

(1) Optical resolution (Optical Rselution)-The resolution of the scanner does not depend on the highest or interpolated resolution (Interpolated Resolution), it depends on the physical optical resolution.

For technical document scanning, it is suitable to choose CIS scanner. Generally, the resolution of 600dpi is enough to meet the application, no matter how high it is, most of these scans will use the resolution of 600dpi or lower, the higher the resolution used. , The storage size of the file will increase in a geometric index.

For art image documents, this kind of application 600dip is slightly insufficient. You can choose the mainstream optical 1200dpi CCD technology scanner on the market, which is enough to meet the application.

(2) Scanning Speed

Generally, all manufacturers use "inches / second" to describe the speed of the scanner. If you go to the site to test or watch the dealer ’s demonstration or exchange activities, you must figure out the speed of the resolution. There is no software acceleration, because the software acceleration mode usually loses image quality.

Because in the end you are to obtain a satisfactory electronic image as the ultimate purpose, in fact, more factors should be considered for the scanning speed, including the warm-up time of the scanner, whether the document loading method is flexible, and whether it can be automatically completed at the same time during the scanning process Such as rotating, cropping images, eliminating manic points, etc., whether multiple scans are required to determine the scanning parameters, whether the scanning software can scan and then process the image function, etc. These factors will greatly affect the overall scanning time, and the final scanned document The time is often higher than the time declared by the manufacturer. That is the time under ideal conditions, which is not consistent with the actual scanning situation. The high-efficiency large-format scanner should be ready for use without preheating; the document loading method is flexible, and can be loaded from the side or the middle; the set operation can be completed at one time during the scanning process without post-processing; Drawing blue can use Intelligent Adaptive Thresholding mode (IAT, Intelligent Adaptive Thresholding). Only one scan is needed, and the parameters of blue suppression can be adjusted arbitrarily in the later stage to achieve satisfactory results. There is no need to adjust the parameters multiple times to scan. It also greatly reduces work efficiency, which is especially important and requires special attention.

(3) Illumination

The mainstream large-format scanners on the market are 16-bit grayscale or 48-bit true color image capture. For large-format scanners, the lighting system will affect the quality of the scanned image, just like the human eye. If the surrounding light is not well-lit, the scene will be unclear. Scanners on the market mostly use cathode cold light sources or LED (light emitting diode) light source lighting systems. Because the LED light source does not require preheating and is ready for use, it has been widely used by large-format scanners. At present, large-format scanners designed on the market using symmetrical dual-LED (Bi-directional LEDs) light source lighting systems have been considered to be able to effectively eliminate shadows and bring better image quality through practical application, especially in conjunction with single-roller shaft transmission mechanisms. When processing documents with creases due to folding, the details at the creases can be better restored.

(4) Interface

At present, the interface of mainstream large-format scanners has been upgraded to a more convenient and fast USB2.0 interface. Such an interface is plug-and-play and extremely convenient to use. With the increasing application of networks, mainstream manufacturers have launched dual interfaces of USB and Gigabit Ethernet. The Gigabit Ethernet interface can overcome the limitation of the USB interface by distance (generally up to 2 meters). In theory, the length can be unlimited. It provides a higher data transmission speed than the USB interface. It can be arbitrarily installed from the network Scan the driver software on the computer.

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