Scanning Technology Characteristics of Book Scanner

At present, most of the professional non-contact scanners in the market adopt the arrangement of the imaging lens and linear CCD. When scanning books, ancient books, newspapers and other original parts, use the change of distance to maintain the correct focus. In the scanning process, the linear CCD sensor will capture the information in the original in the order of red, green and blue lines. When the CCD processor converts these lines into the correct order, the image is composed of the full resolution of RGB value, without the phenomenon of lacking colour channel of matrix CCD.

The linear CCD sensor can convert the light signal on the surface of the original book into an electrical signal. The colour filter provides a very high colour saturation for red, green and blue continuous CCD elements, which is the characteristic of a typical linear CCD scanner. The pixel size of high-quality linear CCD is quite large, 10 μ m × 10 μ m is a typical pixel size value. Larger pixel sizes can help reduce noise and other possible effects on image quality.

In the scanning system, reducing the lens quality has a great influence on the image quality. However, if compared with the lens in the matrix CCD sensor module, the effect is much smaller. Because only the middle part of the lens is used effectively when the lens is collecting images. To get the same image quality as linear CCD, the lens of a matrix CCD sensor must be twice the diameter of the linear CCD sensor. Even in this way, the matrix CCD lens will have an obvious colour difference, geometric distortion and strong loss at the corner.

Matrix CCD sensor module uses a planar CCD composed of very small pixels. At present, the matrix CCD sensors are all arranged on a standard Bayer filter by two green, one red and one blue pixel according to the rule of four times. By using this technology, two times of green channel and four times of red and blue channel are reduced in image acquisition. Therefore, compared with a linear CCD sensor, the biggest disadvantage of matrix CCD is that it will produce quite a lot of noise, and the collected colour is not accurate. These matrix CCD image sensors are not suitable for scanners because they are good at taking pictures rather than scanning. The original intention of the matrix CCD sensor design is not to replace the scanner design, but to get different images according to the different focal length of the target at different far and near positions.