The depth of field for optical imaging system is restricted according to its structure parameters. It is obviously when
optical microscopy is used, which depth of field is very small and it is lesser with larger amplification ratio. In the paper,
three main methods to extend the depth of field will be shown, and their merits and shortcomings will be analyzed. The
first method is to use optical mask. It is easy to achieve satisfied results with calculation simulation, but it is difficult to
produce this mask if it is complicated. The second method is to use image processing. Many images can be obtained
with scanning of imaging system in the direction of depth. Using image processing method, the information of each
image will be extracted, then to compose a new image with them. It is a hard work to capture these scanning images.
And it is difficult to achieve real time image. The last method is to combine the method of optical mask and image
processing. The larger depth of field for optical imaging methods can extend the image range that can be used in the
field of optical microscopy and scanning image system.
Extending the depth of field (DOF) of incoherent optical systems has been an active research topic for many years, and
the extended depth of field (EDOF) system can be used in many fields. We developed a novel circular pure phase plate
to extend the DOF by a factor of 4 without decrease of optical power in image plane. The plate is divided into several
equal-area annular zones and placed in the exit pupil of a standard optical imaging system. The annular zones alternately
eliminate the influence of different defocus beside the ideal Gauss object plane. The comparisons of the MTF and PSF
curves between two systems show that the system employing the phase plate has a large DOF while preserving an
acceptable resolution. Also, the images captured by the system don't have to be restored by a digital filter before next
processing. And the simulation of imaging a spoke target in several defocused condition also confirms the EDOF of the
imaging system. The DOF can be adjusted by two parameters of the phase plate: defocus compensation parameter and
zone number. We gave the relation curves between system's performances and parameters of the plate.
Film is one kind of important record median. Its quality will affect image quality directly. So, it is necessary to study how to assure its quality. Because the situation of film production in dark room, normal detect method could not satisfied the film. In order to avoid to damage film, an infrared detect system is studied. This system is design to set at the position of spreader head. If the defect of film could be found at this position, the beginner of film production line, worker could tread with it in time and reduce waster.
The infrared detect system include two sub systems. The two sub system need to detect one position all the time. One sub system is used to detect if there is defect. One CCD camera captures film image. The film image will be monitor by worker through screen. The screen should be set in light room. Another sub system is composed of object lens, image intensifier micro-channel plate and eye lens. If worker find defect from screen, he will inform another worker who worker in dark room. Another worker could find the defect through image intensifier system, and treat with it. The communication method between two workers is sound, not alarm light, because there is dark room. All of the two sub systems use infrared light as light source. The wavelength of light source is 940 nm, which is safe to film.
This system is designed for Lekai, the biggest film company of China. This system could find detect early and help worker to deal with it on site, because the detect position is the starting of film production line.
Wide film detect system, studied in the paper, is one kind of industry vision system. Wide film is useful recording medium, such as photograph, press and medicine. In the course of production, one main problem is the film is scathed by these transmit rolls. It will affect later imaging effect directly. How to assure its quality is an important task. Now, the film detection is a manual work and only some selected samples could be detected. The detection will be done after all production courses are finished. So, it is a difficult task to assure the film quality.
In the paper, a wide film detect system was studies. The film detection task could be real-time operated when the wide film detect system is assembled with production line. The film detect system, like other industry vision system, is composed of optical system, CCD sensor, image frame grabber, light source and computer. The detection principle is based on image processing method. One point need to be shown, that is a suit light source is very important to the whole detection system. The light source shouldn't damage the film and it must have enough power to assure the CCD sensor could detect. Infrared LED, which main wavelength is 940nm, was selected as source light. The detection speed is up to 90 m/min, detection width is 1300mm and detection resolution could up to 0.5mm at the operation direction and 0.05mm at the film width direction.