In the field of printing, the printing of three-dimensional space to reproduce three-dimensional images of objects-three-dimensional printing has become an important content in the special printing industry. Let's talk about the technical characteristics and development prospects in this regard.
1. The principle and characteristics of three-dimensional printing
The principle of three-dimensional printing is to simulate the distance between human eyes, shoot from different angles, and record the left and right pixels on the photosensitive material. When viewing, the left eye sees the left pixel and the right eye sees the right pixel. The printed product made according to this principle is called For three-dimensional printing.
Three-dimensional printing has the following characteristics: (1) It can reproduce objects realistically and has a strong three-dimensional sense. The product image is clear, rich in layers, vivid in image, and deep in the mood; (2) The three-dimensional printed manuscript is often taken from the shape design or the scene. The printed matter is generally selected for high-quality coated paper and high-temperature ink, so the gloss is good The color is bright and not easy to fade; (3) The surface of the printed product is covered with a layer of concavo-convex cylindrical mirror grating plate, which can directly watch the three-dimensional effect of the panoramic picture. From the perspective of people's stereoscopic vision of objects, the stereoscopic vision of objects is mainly derived from human physiological factors, experience and psychological factors. In fact, stereoscopic vision is the stereoscopic information formed by the synthesis of these complex factors of appeal in the visual process. In terms of physiological factors, there are parallax (binocular parallax and monocular parallax), convergence, and adjustment. Specifically, binocular parallax is the fundamental factor for people to obtain stereo vision, that is, in daily life, when people observe an object, due to the angle of view between the two eyes, the image of the object seen by the left and right eyes will be different, namely Parallax, it gives people a three-dimensional sense.
The effect of the stereoscopic image must be reflected by the display technology. The stereoscopic display mentioned here refers to the reproduction of the stereoscopic information in the three-dimensional space of the image, which is another basic condition for obtaining stereoscopic vision. There are two main methods for realizing stereoscopic display, namely two-way display method and multi-way display method.
(1) Two-way display method. Can be divided into three-dimensional mirror method, two-color filter method, polarized filter method and alternate division method. No matter which method is adopted, stereoscopic vision is obtained by observing the images separately with the two eyes and the left and right eyes. Stereoscopic method: The basic principle of the stereoscopic method is to use the stereoscopic mirror to observe the left and right figures to form a three-dimensional effect. This method has been widely used since the advent of the 19th century, but special stereoscopic mirrors must be used, otherwise there will be no stereoscopic vision. Two-color filter method: the left and right images are printed on the same plane with red and blue inks respectively, and the printed image is observed through the red and blue filters. Since the color filter and the ink are complementary to each other, the image observed through the color filter is not red and blue but black. Therefore, this method is limited to black and white photographs and is not suitable for color prints. Coupled with the different wavelengths of light entering the two eyes, it is easy to fatigue the eyes. Therefore, this method is generally rarely used except for making aerial maps. Polarized color filter method: the left and right images are projected on the same plane through polarized color filters that are orthogonal to each other, and the left and right eyes are also observed with the same polarized color filter. Although this method requires special glasses, it has been widely used in stereo movies and stereo televisions. Alternate segmentation method: the left and right images are alternately presented on the same plane and the unnecessary parts of the same period are masked to produce a three-dimensional sense. Since the afterimage effect causes flashes and the glasses for masking are expensive, this method has not been popularized so far.
(2) Multi-directional display method. There are parallax shielding method and cylindrical lens method. Parallax masking method: The parallax masking method, also known as the parallax slit method, was invented by FELves in 1930. Its working principle is to divide the left-eye image and the right-eye image by the slit and expose it on the film, then develop, Exposure and printing. If it is placed at the same position as when shooting, the two eyes are also placed at the position where the image is placed, and you can see the stereoscopic image. Using the parallax slit method, if two images are synthesized, a parallax stereoscopic image can be obtained. If the aperture ratio of the slit is reduced, multiple images can be synthesized, and a parallax panoramic image can be obtained. The parallax slit method is essentially that the diminishing amount of light is inevitable. Therefore, it is generally seldom used except for photographing by the cylindrical lens method. Cylindrical lens method: Cylindrical lens can be regarded as a lens plate composed of many convex lens sheets side by side, it has a split image effect. The back of this lens coincides with the focal plane. Due to the splitting effect of the lens, the images A, B, C, D in all directions can be separated into a, b, c, d and recorded on the focal plane, as long as the left and right eyes are placed on the B and C Location, you can see the stereo image.
2. Three-dimensional printing process and main points
1. Photography method of three-dimensional printing
As mentioned above, the cylindrical lens method for three-dimensional printing requires images of the illuminated object seen from all directions. Photography methods include (1) circular arc moving method. This method uses a certain point on the subject as the center of the circle, and the distance from this point to the camera as the radius to make an arc. The camera moves along this arc and shoots continuously or intermittently; (2) Parallel movement method. Move the lens parallel to the center line of the object. When shooting with this method, the accuracy is not easy to grasp; (3) Straight line shaking method. The captured image will be somewhat out of shape. But if higher accuracy is not required, this is a simple method.
In addition, the method of not using a cylindrical lens in photography is the same as a normal camera, moving while shooting, and then synthesizing images in all directions through a cylindrical lens. Therefore, images in all directions (6-9) cannot be continuous. It mainly has instant photography. Cameras with multiple (6-9) lenses are most suitable for outdoor photography, especially for moving objects, due to their ease of carrying. It is just that a stereo photo cannot be formed without post-synthesis, which has the advantage of enlargement in size during image synthesis. Ordinary camera movement method: Install the ordinary camera on the electric chute, and slide while shooting. Compared with the above-mentioned instant photography method, there are no outstanding advantages, but no special camera is needed. The method of using a cylindrical lens during photography can continuously shoot within an effective angle. You can get a three-dimensional image at a time, but it is very difficult to zoom in after shooting, and the exposure time is long, you can not shoot moving objects, and the camera is large, so it is not suitable for handling. The object movement method is the opposite of moving the camera, which is to rotate the object and move it linearly. The center of the large turntable coincides with the center of the object to be photographed while the turntable moves. To use a dedicated indoor camera, it is not possible to shoot moving objects; camera parallel movement method: use the method of parallel moving camera to perform equidistant photography on the subject. With parallel movement, the camera is always aimed at the center of the subject. Get good images. However, the production of the camera is very difficult, and because of structural limitations, it is only used for indoor photography; the camera linear shaking method: this is a slightly simplified method than the above parallel movement method. The camera moves in a straight line to the left and right, and the lens repeatedly shakes to align the center of the subject. This method can be used for both indoor and outdoor photography; shutter movement method: this shooting method is limited to indoor close-range photography cameras. The shutter movement method uses a large-aperture lens, which can capture stereoscopic images in all directions as the shutter moves within the lens. This method has less lens movement distance and can be exposed in a short time. At the same time, close-range photography will not damage the three-dimensional sense, and is particularly suitable for portrait photography.
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