2. Transmittal Adapter
Is it necessary to use special film scanners for scanning film? the answer is negative. In fact, by adding a less expensive transmissive media adapter (TMA), a flat-bed scanner can capture digital images that basically meet our needs from transparencies.
The principle of the transmissive document adapter (see Figure 1) is very simple. It uses a light source instead of the scanner's original cover. It moves the scanning light source from underneath the manuscript to the top of the manuscript, allowing the light transmitted through the manuscript to pass through the lens and several mirrors. Imaging on the CCD surface. According to the different types of light sources and scanning methods, the transmissive document adapter can be divided into two types: light source movable type and light source fixed type. The former is a more traditional transmissive document scanning technology. In the upper cover, which is not only small in thickness and weight, there is a set of mechanisms similar to the mobile imaging part of the scanner, but the upside down is reversed - the bottom is a layer of glass. Upward is a light source composed of lamps, followed by a guide rail and a drive motor. When the transmissive film is scanned, the lamp in the transmissive document adapter runs synchronously with the imaging member below and scans the entire web together to obtain a transmitted light image. Of course, in the process, the original light source in the flatbed scanner does not emit light, so that reflections on the surface of the transmitted document do not affect the scanning effect. In contrast, fixed transmissive document adapters are easier to understand, and they are also referred to by some manufacturers as Light Lids. As the name suggests, it is like a special “canopy†that emits uniform light, illuminating the entire scan area, allowing the imaging section to read the information of the transmissive document with ease. Take Microtek's Light Lid transmission and scanning equipment as an example. It consists of two cold-cathode tubes, located on the left and right sides. The light emitted from them is evenly distributed by the special materials below. Due to the absence of a transmission component, the Light Lid is very simple in construction and lighter than a mobile transmissive document adapter.
Usually, the area of ​​the frame we scan is smaller than the illumination width of the transmissive document adapter. When scanning, the light will be transmitted next to the manuscript. These stray light will affect the sharpness and color of the scanned image and cause the contrast to deteriorate. In order to solve this problem, transmissive document adapters are usually equipped with film frames corresponding to various film sizes, which can block the area next to the screen during scanning, ensuring good image quality.
Transmissive document adapters are commonly used in high-end platform scanners. Mobile light source transmissive document adapters have relatively high brightness and accuracy. Many professional platform scanners for printing and design applications have been equipped with such transmissive document adapters when sold, such as Microtek ScanMaker 9600XL and Tsinghua Unisplendour Dunhuang D2000. HP ScanJet 6330C, Umax PowerLook III, AGFA Arcus II, and more. The fixed light source product has a low cost, and there is no situation where the light source motion and the scanning part are not synchronized. However, due to the large illumination area, the unit light intensity is low, and it is also difficult to scan large-format transmissions. Typical of such products are Microtek ScanMaker X6EL, AcerScan 620-T, N-Tek Nuscan 6063EL, and the like.
In general, the method of adding a transmissive document adapter to a flatbed scanner is relatively inexpensive, and it is the most easily selected transmissive document scanning solution for ordinary users. However, due to the limited optical resolution of the flatbed scanner, the dynamic range is usually not high, and it is difficult to obtain images with excellent quality, so the use is generally limited to general office or web page production. In addition, because the transmitted light adapter and the two glasses on the scanner sandwich the transmissive document, which restricts the improvement of the scanning quality, not only the aberration caused by the glass irregularity, but also the phenomenon of “Newton's ring†is easily generated, which greatly reduces the The final image effect.
3. Dual-platform scanner
There are problems such as the above mentioned with the flatbed scanner plus the transmissive document adapter, and the quality of the image is not very high either. Therefore, the manufacturer has developed a new transmissive document scanning technology, the dual-platform technology, which can be used in a flatbed scanner and can achieve a transmissive document scanning effect comparable to a dedicated film scanner.
The dual-platform technology perfectly achieves the input of both transmissive and reflective documents. In appearance, the dual-platform scanner is a bit like "sandwich" bread, and a "drawer" is specially prepared in the middle to place the transmitted manuscript. For ordinary reflection drafts, the dual-platform scanner uses the traditional imaging light path and scanning operation completely; but it also sets up a separate optical system for the transmissive document (see Figure 2). In addition to the CCD sensor and the lens, the light source, The mirrors are completely different. Because the transmitted manuscript is only fixed by the frame, it can adapt to manuscripts of various sizes, and the aberration and Newton ring brought by the glass are avoided, so that the scanning quality and efficiency can be greatly improved.
Scanners with dual-platform technology use multi-lens technology to increase the effective optical resolution. Because the linear CCD sensor used by the scanner has a fixed number of pixels, the smaller the coverage scan size, the higher the optical resolution. Take an 8000-pixel CCD sensor used in high-end scanners as an example. If the scanning width is A4 (8 inches wide), the optical resolution is 1000 dpi. If the focal length of the imaging lens is adjusted, the maximum scanning width is changed to 4 inches. The rate can be increased to 2000 dpi, which is the principle of multi-lens technology to increase the resolution. Multi-lens technology seems to be very simple, as long as a series of lenses with different focal lengths are set in the scanner, and can be replaced at any time according to the different requirements of the scanned manuscript. However, the imaging light path of the scanner requires high precision. Each time the lens is replaced, a large number of components will generate rotational motion. This requires a high-precision transmission mechanism to ensure that the cost of manufacturing and debugging the multi-lens scanner is relatively high.
Dual-platform dual-lens scanners can perform excellent scans of transmissive films, ideal for resolution, dynamic range, or scan format, while enabling high-quality reflection draft scanning. At present, the dual-platform scanners are high-end products worth tens of thousands of yuan, such as Microtek ScanMaker 2000, ArtixScan 2020, and AGFA DuoScan, which are suitable for professional design, printing and publishing applications.
In addition to these above-mentioned transmissive document scanning solutions, the scanner camp also has a veteran-professional drum scanner, which picks up image information point-by-point through photomultiplier tubes, which can achieve high resolution and dynamic range, especially The level of shadows is rich and accurate, and it is an ideal solution for transmissive film scanning in terms of quality. However, drum scanners are expensive, scan speeds are slow, and the application area is getting narrower and narrower.