When you choose a professional non-contact book scanner, you need to know what is the key factor.
Extra-curricular books, textbooks, magazines, and historical documents have different colors, shapes, and sizes. For libraries, archives, and museums, the digitization needs of historical data are facing greater challenges. When establishing and investing a suitable digital platform, the choice of professional book scanner camera type is a very important link. The purpose of this article is to provide some basic information to help you understand and judge the key functions and take quality control of the digital system, avoiding detours and making the right choice.
At present, there are mainly two kinds of book scanner systems in the market according to the purpose of use: overhead linear CCD scanner composed of linear scanning CCD sensor, lens, and light unit and overhead camera scanner. In overhead linear CCD scanner, linear CCD, optical system and illumination system are integrated as a whole and move as an independent module on the scanned document. However, in the overhead camera scanner, a digital lens (or matrix CCD) is fixed above the scanned document to collect images. The lighting system is attached to the equipment through light sources, and even some equipment does not provide lighting, which is completely provided by environmental light sources.
Both books and periodicals scanner systems use CCD sensors for imaging. The CCD sensor is a precise and complicated technical equipment. Its main function is to acquire image information in different image capture and acquisition systems. The main advantage of CCD sensor technology is that it is extremely sensitive to light. Through interference with useless information, clear images can be obtained, for example, images with little noise can be obtained. Because the structure of CCD is relatively simple, CCD sensors manufactured by semiconductor manufacturers seldom have bad spots (i.e. defective pixels), so the possibility of bad spots on the entire CCD sensor is also small, while linear CCD sensors are the only sensors that can transmit information without errors.
The difference between linear CCD and matrix CCD
The key difference between the above two book scanner systems is whether the CCD sensor is linear or planar, sometimes the latter is also called a matrix sensor. In linear CCD linear sensors, independent photo-sensitive pixel points are arranged in a row. The two-dimensional image is obtained by linear movement of the linear CCD sensor on the original, and the integrated linear CCD sensor moves accurately according to the distance of each pixel point when moving. In order to obtain a color image, each pixel is composed of red, green and blue, and then three parallel linear CCD arrays are formed, each row is provided with color filters, and the color image is obtained through color separation technology.
The linear CCD length of standard overhead linear CCD scanner ranges from 7500 to 10680 pixels. In some special requirements, the linear CCD length can even exceed 20000 pixels. In the three-color linear CCD, the pixels of each color are 7500 pixels, then the three-color linear CCD sensor has more than 22500 independent pixels (3x7500=22500), so the total resolution of the scanning system is equal to the number of pixels of the three-color linear CCD sensor multiplied by the number of pixels in the scanning direction. Based on this, compared with the overhead camera scanner, an overhead linear CCD scanner can obtain high-resolution images without a software interpolation algorithm.
For planar CCD or matrix CCD sensors, independent pixel points are arranged on a plane, and each pixel point obtains one of the three RGB colors through an RGB filter. In order to collect all the color information, either every pixel on the whole matrix CCD sensor is converted and read many times, or only the color information of adjacent pixels can be collected to compensate for the lost color by software interpolation. At present, the largest matrix CCD sensor in the market can reach 7000x10000 pixels, that is 70 million pixels, but this kind of matrix CCD sensor is very expensive.
The quality of digitized images depends on several different factors, among which real resolution, color reproduction capability, and uniform illumination are the most critical factors.
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