Do you pay attention to the precise information of every detail or just take a rough understanding?
To evaluate the quality of professional scanners, image resolution is the key factor. Resolution is a key indicator of the scanner's ability to reproduce accurately or roughly. The higher the resolution is, the more accurate the details and levels collected from the original file will be.
Comparing the two types of CCD scanning systems, the real resolution is very important. In other words, software interpolation cannot be used to improve the resolution. Generally speaking, the CCD sensor data of one million pixels is used to describe the total resolution of the scanning system, but in fact, the real resolution is significantly lower than this. A 40-megapixel chip contains 20-megapixel green information, 10-megapixel red information, and 10-megapixel blue information. This means that only one-third to one-fourth of the pixel points of a million-pixel CCD sensor has a real resolution, and the rest are implemented by software interpolation. Therefore, the resolution of a 40-megapixel matrix CCD sensor scanner is equivalent to that of a 10-megapixel or 13-megapixel linear CCD sensor scanner. Compared with the matrix CCD sensor scanner, a linear CCD sensor scanner shows several times the higher real resolution.
Resolution: advantages of linear CCD sensors
The same A2-sized original is scanned by two types of CCD sensor scanners. The comparison is as follows: the overhead camera scanner uses a 40-megapixel matrix CCD sensor, and the color mosaic filter needs to allocate 20-megapixel green information, 10-megapixel red information and 10-megapixel blue information from the 40-megapixel CCD to obtain complete image information; the overhead linear CCD scanner, using 7500 image-length linear CCD sensors, can obtain 10140x7500 pixels of information, or 75 million pixels per color channel, or a total of 2.25 million pixels of red, green and blue. Therefore, the resolution provided by the linear CCD scanning sensor is 6 times that of the matrix CCD sensor.
Because the total number of pixels of the matrix CCD sensor is huge, bad pixel points always appear on the pixel points of the matrix CCD sensor. According to the general commercial calculation rules, for a matrix CCD sensor with an effective pixel of 50 million pixels, there may be 4,000 bad pixel points, of which there may be up to 50 bad pixel cluster rows and 20 bad pixel cluster columns. When collecting image information, these damaged pixel areas must be corrected by software interpolation. Due to the algorithm problem of software interpolation, the color information of normal pixel points adjacent to the bad pixel points will be modified by mistake while the software is corrected. In fact, even if the software interpolation is correct, it is only as close to the true color as possible.
Besides, it is also a good idea to consider the problem of "color interpolation". Most matrix CCD sensor scanners are limited to the fact that only one color can be sampled per pixel, and the lost color information can only be generated by software interpolation of adjacent pixel points. When "color interpolation" is used to process high-definition and high-contrast original documents, the image will be distorted due to the "moire effect". In order to solve this problem, when making digital instructions, the German Research Foundation proposed to use a linear CCD scanner when scanning delicate patterns and intaglio printing data.
Users should not be confused by the high pixel information claimed by the matrix CCD scanner supplier, because for matrix CCD sensors, what matters is the actual resolution, not the software interpolation resolution.
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