In order to measure the lightness and darkness of the draft and the transmitted document in a simple manner, the reflectance and the transmission density are used to represent the light and darkness, respectively.
Reflection density is: Dr = lg1/R
Transmission density: Dt=lg1/T
See Table 1 for the relationship between reflectivity R, transmittance T, and dynamic range.
The dynamic range of the scanner has a direct relationship with the number of digits of the scanner. The dynamic range of the scanner is represented by a logarithm to the base 10 of the light and dark levels. If the 24-bit scanner can express gray levels of 256 levels, so the maximum dynamic range is: D = lg256 = 2.4, but the 24-bit scanner can not fully show the 2556 level, the general dynamic range is 2.2, the scanner The gray level that can be expressed is 10 to the power of 2.2, which is 159. The dynamic range of the 30-bit, 36-bit, and 48-bit scanners is shown in Table 2.
It can be seen from Table 2 that the more digits of the scanner, the greater the dynamic range provided, and the larger the dynamic range of the scanner with the same number of digits, the more layers it can represent.
4. Magnification Magnification refers to the magnification of the scanner to reduce or enlarge the original.
Scaling is a processing program that generates a larger or smaller image in the scanning software. When the scanned image is fed into the image editing program, there is no need to change the size of the image again.
In the scanning software, the scaling ratio is inversely proportional to the resolution. The lower the resolution, the larger the scaling of the image. When using the maximum resolution, the scaling can only be less than 1.
To illustrate the use of scaling, assume that a 2in*2in image is scanned at a resolution of 300DPI, and that without loss of detail and a 4in*4in magnified image is desired, the scaling factor should be set to 200% and the resolution to 300DPI.
The result of the 600DPI resolution and 100% scaling scan is the same, but the latter must be changed by the image editing software to change the resolution to 300 DPI (the file size remains unchanged) before output. In the above example, the size of the image is changed by adjusting the scaling instead of using image editing software.
V. Scanned Originals Scanned originals refer mainly to photographs, texts, graphics, and illustrations. Even three-dimensional objects such as coins, watches, or textiles are regarded as originals, collectively referred to as scanned originals.
When it comes to scanning a manuscript, it is often described as an original manuscript. The original index refers to the scanner's ability to adapt to the original. It can be expressed by the original type, original size, and original density range.
1. Original Type The original type refers to the linesmanuscripts of transmitted originals, reflected originals, color positive and color negatives, color originals, and black and white originals.
A transmissive manuscript refers to an image that can be viewed through the light through the manuscript, and it includes a variety of upper-sized transparencies (including 35mm slides) and all negatives.
Reflective draft refers to an image that can be viewed from the reflected light on the surface of the original. At present, a large number of scanned originals are reflective drafts such as photographs, newspapers, magazines, books, pictorials, etc.
The color print is also called a positive picture. On the positive film, the color and hue of the image are the same as we normally see. Such as 35MM slides. Negative film is also called Yin picture. On the negative side, the color and tone of the image are the opposite of what we normally see. Such as the negative film used by the camera. Using a negative film for the camera will make the photo better, but it is convenient to observe the water. If the film requires direct observation, positive film can be used. When you take a film that is specially used for scanning, it is usually shot at the spot so that you can directly check the effect of the image.
Near the color of the image, the original can be divided into black and white originals and color originals.
Black and white manuscripts refer to black-and-white images, such as text drafts, black-and-white newspapers, pencils, and quick-drawings of brushes. Line draft is also a kind of black and white manuscript, mainly referring to engineering line graphics. Color manuscripts refer to color images such as landscape paintings, figure paintings, color posters, posters, and so on.
2. Maximum size of the original The maximum size of the scanned original is the maximum size of the original scanned by the scanner. This index is important for reflective drafts. Because of the large size of reflective drafts, the drum and flatbed scanners of drum scanners have certain restrictions. To accommodate different sizes of originals, manufacturers have also introduced scanners of different sizes, commonly used in A4 format. , A3 format scanner, A0 format, A1 format engineering drawings scanner.
Transmittals are generally small in size, with the smallest typical dimensions being 35m, \60mm x 60mm, 60mm x 70mm, and 4in x 5in. With a dual-platform scanner, the broom is dried, in×10 in, and 12 in×18 in.
3, the original maximum density range The original density range, refers to the original minimum density and the highest density difference. The maximum density range of an original refers to the scanner's limitation on the density range of the original. Only within this density range can the image scanned by the scanner have a good level of reproduction. The density of the manuscript can be measured by a densitometer. The density of a typical printed matter is 0.06-2.2, and the density of the reversal film is 0.02-4.0. If the density of the original is large, and the range of the scanner's density is not enough, the scanned image is difficult to reproduce the level of the original, and it is necessary to scan with a scanner having a higher density range.
6. Scanner Speed ​​The speed of the scanner has a close relationship with the system configuration, scan resolution settings, and scan size. Under normal circumstances, scanning black and white, gray-scale images, scanning speed of 2-100 msec / line; scanning color images, scanning speed from 5-200 msec / line.
There is a conflict between scanning speed and image quality. Under normal circumstances, people always want the scanner to be fast, but the scanner works by using the light source of the scanner, using a color separation method and a charge coupled device (CCD) array to collect the optical information of the scanned object. It takes a certain amount of time to acquire the image information and transfer the information to a computer image file. The scanner speed is good, but it does not affect the image quality. Therefore, it is not the scanner that scans as fast as possible. A very high speed scanner may lose some scanned image information during the scanning process. Some scanners scan fast at low resolutions, but scanning speeds at high resolutions are not necessarily fast. Therefore, the speed of the scanner must be improved under the premise of ensuring quality.
In addition, the scanner has other indicators, such as the number of scans. The black and white scanner has only 1 scan. The early gray-scale scanners and color scanners used 3 scans. With the introduction of color CCDs, the technology of scanners has also evolved. The three-scanning technology has become obsolete. At present, color scanners are scanned one more time.