On stereoscopic printing and its application

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On stereoscopic printing and its application

1 The origin of stereoscopic printing

since the British physicist invented the stereoscope in 1838 and the Frenchman niepchi took the first stereoscopic image photo based on the "visual persistence" theory in 1882, after more than 100 years of continuous pursuit and exploration by a large number of scientists, the stereoscopic image technology has finally entered the era of stereoscopic photography in the 1990s, following the black-and-white and color generations. Leave everything in an instant, round the human dream for a century, reproduce the three-dimensional world on the two-dimensional plane, and make the three-dimensional feeling of human vision enter a new field. Everything in the world is three-dimensional and three-dimensional. Any object in space has a three-dimensional shape of length, width and height, that is to say, objects have a relationship between front and back, left and right, up and down, but reflected in photos and general printed matter, it can only show its two-dimensional relationship of up and down, left and right, losing the sense of three-dimensional. In order to emphasize the stereoscopic sense of the objective world, people have developed a new printing field - stereoscopic printing. Stereo printing is to simulate the distance between human eyes and shoot from different angles,; Lower the left and right pixels and record them on the photosensitive material. The left eye sees the right pixel and the right eye sees the left pixel. According to this principle, the printing technology of producing printed matter is called stereoscopic printing. Therefore, we can say that stereoscopic printing is a printing method that uses the parallax of left and right eyes to cover the grating column panel to obtain a stereoscopic image

2. Basic principle of stereo printing

stereo printing requires taking two negatives with a double lens stereo camera equivalent to the human eye, taking stereo photography, and drying them into printing plates equivalent to the images seen by the left and right eyes respectively. Then stagger the printing at a certain angle. In order to see the image clearly, we must add a thin concave convex transparent plastic sheet on the printed matter, which is called column lens for short. This column lens is very critical, and its concave convex interval is 0.6mm. The concave convex surface divides the image into countless pixels at equal distance. There are 120 concave convex lines/inch, and there are 6 pixels under each line. These pixels form overlapping images staggered by a certain distance on the plane. With the help of the cylindrical lens, this staggered distance forms a space, so that people can feel the depth between the front of the scene and the background, so that the image information can obtain a three-dimensional sense

3. Prerequisites for stereo printing

stereo photography is a prerequisite for stereo printing. The methods of stereo photography can be roughly divided into direct method and indirect method. Direct method refers to the method of photographing directly through the transparent column lens. Moving the lens within a certain field of vision will continuously photograph the subject, and the effect is better. The indirect rule is to take more than two photos from a predetermined position, and then synthesize them correctly in a space. Considering the form of the printing plate, the effect of printing with collotype is the best, because it has no point of interference, but because the printing volume is limited, offset printing is generally used at present

first take photos with a 300 line/inch screen, and then make a positive color separation sheet. With a positive color separation sheet, when printing, in order to make the printing plate made of four color separation sheets overprint into a virtual image, it is necessary to stagger the printing, and the dislocation phase of the four color separation sheets shall not exceed 0.6mm

when pasting transparent column lens on the printed false printed matter, in addition to keeping the concave convex interval of 0.6mm when pressing the transparent column lens, it is also necessary to limit the thickness of the column lens, which is too thin to be cast into concave convex shape, and excessive thickness will damage the three-dimensional f) automatic calibration: the system can automatically calibrate the accuracy of the indication; Sense, generally 0.2-0.3mm is appropriate

4. Overview of stereoscopic printing technology

there are many kinds of stereoscopic printing. The process of ordinary stereoscopic printing mainly includes the following steps:

the principles of various stereoscopic printing processes are basically not very different, but they are improved in individual process details, but at present, data collection, PID operation The stereo printing technology of all control processes from Ethernet communication to output control can be divided into the following types according to the observation mode:

two color stereo printing, with complementary two-color printing, and the three-dimensional effect can be seen with two-color glasses

in ordinary stereoscopic printing, the negative of stereophotography is processed, and the stereoscopic image is seen according to the refraction of light through the cylindrical grating method

dynamic stereo printing, which is an extension of stereo printing technology. First of all, we need to prepare a distinctive animated photo, which is made of 18 film frames overlapped in turn. Use this photo as the original, add a concave convex thin transparent plastic plate in front of the photographic plate of the camera, and then place a 300 line/inch screen in front of this plastic plate at an appropriate distance. When everything is arranged properly, the reflected light of the photo passes through the screen and plastic plate and reaches the photosensitive film, that is, a photographic negative with a chain image of Juxian decomposed by pixels is made. With this plate making and printing, a dynamic picture can be made. Transparent cylindrical lenses must also be attached to the picture to achieve the purpose of direct viewing with the naked eye

holographic stereo printing, which is formed by molding the laser holographic stereo photographic negative after processing, and the color and image can be seen through the interference of light

laser holographic printing technology, when taking photos, the laser is diffused and irradiated on the subject by convex mirror, and the light reflected from the subject reaches the film surface. The reference light, another column of laser light irrelevant to the subject, also reaches the film surface after being reflected by the mirror. When two parts of the laser are overlapped, thin lines called interference lines are produced. A film with such thin lines is called a hologram. By irradiating the hologram with a laser, the image in the line can be reproduced. The making and reproduction of holograms are collectively called holography or holography

three dimensional printing, which is printed from the three-dimensional original processed by the computer, and the three-dimensional effect can be seen through staring

concave convex embossing, which is processed on the printed paper or plastic surface to produce a three-dimensional effect for direct viewing

5. Common stereo printing technologies and their comparison

among the currently used stereo printing technologies, the most common stereo printing technologies are ordinary stereo printing, dynamic stereo printing and holographic stereo printing. Here, we will use the method of comparison to elaborate these three-dimensional printing technologies

the stereo photography of ordinary stereo printing mainly adopts the method of circular arc moving photography, that is, taking the center point of the subject as the center of the circle, and taking the radius from the center point to the focal length of the photosensitive sheet as the radius, the cylindrical lens plate is directly installed in front of the photosensitive sheet, and moves randomly and synchronously. Each exposure will focus a pixel under each semicircular column of the grating plate, Finally, it covers the whole grid distance. Stereoscopic photos can be obtained by developing. Like other printing methods, the plate making process of stereoscopic printing also includes color separation, addition, plate printing and other processes. It is worth noting that in the color separation of stereoscopic printing, the number of scanning lines is generally more than 400 lines/cm. Due to the delicate pixels of stereoscopic images and the amplification effect of cylindrical lens gratings, in order to get better prints, we should use more fine-grained processing. The line angle in stereoscopic printing should not be 0 ° angle. In addition, the addition angle of C and K plates in stereoscopic printing should be consistent, and the field density of color ink should be high. The overprint accuracy of ordinary stereoscopic printing is very high, and PS version is generally used. Stereoscopic printing can be printed in different formats. The finished product can have a stereoscopic feeling only after the surface is covered with cylindrical lens grating. At present, there are two kinds of cylindrical lens grid plates: hard plastic and soft plastic. The former mainly includes polystyrene and the latter mainly includes polyvinyl chloride. Before compounding cylindrical lens, it is necessary to make a cylindrical lens female template according to relevant parameters, and then form it while laminating. The commonly used methods mainly include flat pressing, roller pasting (as shown in the figure below) and back pasting

dynamic stereoscopic printing is an extension of ordinary stereoscopic printing, that is, dynamic pictures are printed on the basis of stereoscopic pictures, and dynamic products can be produced as long as the observation angle is changed. The production principle and method of dynamic stereoscopic printing are the same as that of ordinary stereoscopic printing. Dynamic stereo printing also needs to take stereo photography of the original first, but unlike ordinary stereo printing, it needs to determine the number of actions to design the original; Each action has a picture, and the number of actions determines the number of negatives used. The original of dynamic stereoscopic printing now generally adopts the desktop printing system for color separation to obtain multiple sets of color separation negatives (negatives). The negatives obtained are copied to combine multiple action pictures on one negatives, which need to be exposed step by step. Finally, the positive pictures corresponding to the action pictures are obtained by developing and fixing, and then the dynamic stereoscopic printing is obtained by printing, printing, and composite cylindrical lens plate

holographic stereolithography is a reproduction technology that transforms the interference fringes formed by laser photography into stereoscopic images and appears on specific substrates. It is a new stereolithography technology developed on the basis of holography. In the 1980s, holographic stereoscopic printing technology entered the stage of promotion and application, holographic stereoscopic printing began to popularize and gradually realize commercialization. The process flow of holographic stereo printing is shown in the figure below. Holographic stereoscopic printing is not made by printing with ink. This kind of printing is similar to the method and process of conventional printing. Holographic stereoscopic printing first needs to shoot holographic images. Before taking a hologram, you should choose the appropriate theme and the best layout of its space, and pay attention to the influence of light. When the hologram is not properly illuminated, it does not show any characteristics of the recorded scene. Rainbow holograms are taken according to the diffraction characteristics of light. It is made by placing photoresist light sensitive plates through exposure, development, fixing and other processing. In holographic stereolithography, a soft photoresist material will be used, but it is not suitable for direct imprinting, so it is necessary to make an imprint template, which is often a metal template. After transferring the rainbow holographic image information, it is imprinted on the molding machine. The purpose of imprinting is to transfer the image information on the imprinting template to the transparent film or vacuum aluminized film at a certain temperature. The films commonly used for embossing mainly include PVC, pet, PS, PP, etc. the embossing process is carried out according to the process of hot pressing, cooling and stripping. After imprinting, vacuum aluminum plating is required, which is mainly to achieve the purpose of direct viewing of holographic images under white light. It is a process of atomizing aluminum wires and depositing them on the imprinted film under high vacuum conditions. At present, aluminized film can also be directly used for embossing. After that, it is necessary to apply glue and film to facilitate the transfer of stereo image information. The process mainly includes the processing of paste type and hot stamping type holograms. At present, the quality of holographic stereoscopic printing is not ideal and needs to be further improved. With the popularization and development of computer technology, many manufacturers have used computers to make stereoscopic images, which has made stereoscopic printing technology develop well

6. The application of stereoscopic printing

stereoscopic printing is the further development of stereoscopic photography and stereoscopic display

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