1. The relationship between grid distance (p), thickness (d) and observation distance (D)
Due to the influence of the human eye's resolving power, we can distinguish more details from near objects, while the ability to perceive the details of distant objects will drop a lot. As for the grating on the stereoscopic image, if we can clearly discern the grating rods, it will interfere with our visual experience and affect the performance of the stereoscopic image. When the thickness is constant, the reduction of the grid pitch will increase the observation distance. Therefore, it is not possible to start with changing the pitch alone, but also to consider the thickness factor. If the thickness of the grating plate is reduced at a specific pitch, the viewing distance will become smaller. Therefore, the grating plate used for close-up observation should be thin and dense. For the grating plate used for long-distance observation, some details of the drawn image are lost if the grid distance is too small, but it will affect the observation effect. Similarly, in order to meet the requirements of wide pitch, it is necessary to increase the thickness of the grating plate. Therefore, the grating plate used for long-distance observation should be thick and sparse.
To sum up, when manufacturing the grating plate, it is necessary to determine the appropriate grating distance according to the required observation distance, and then to determine the thickness of the grating according to the observation distance and the grating distance.
2. Parameter analysis
The above is analyzed from the relationship between the parameters, and the impact of the selection of parameters on the image effect is analyzed below.
â‘ Raster line number (LR)
The number of grating lines refers to the number of grating lines included per unit of inch, which is the reciprocal of the grating pitch p. The line number of the grating is expressed by LPI, that is, the number of lenticular lenses within 1 inch. There are generally suitable gratings for printing: 75LPI, 100LPI, 120LPI, 150LPI, etc.
The number of lines of the raster film determines the accuracy of the stereoscopic image, which limits the resolution of the raster image. The higher the line number of the grating, the higher the resolution of the raster image. The accuracy of the final stereo image will be higher; the line number of the grating is lower, the resolution of the raster image is Without being too high, the accuracy of the final stereo image produced is relatively low. The higher the resolution of the raster image, the higher the requirements on its output device, and the higher the natural output cost. Therefore, when selecting the number of lines of the grating plate, it is necessary to meet the accuracy requirements and the production cost should be within a reasonable range while meeting the accuracy requirements.
The resolution of details by the human eye is limited by the observation distance, so in actual production, the number of grating lines should be selected according to the observation distance. A grating plate with a high line number should be selected for close-up observation, and a grating plate with a thick line number should be selected for long-distance observation.
Generally, when the observation distance is less than 80cm, the grating plate of 75LPI ~ 90LPI should be selected, at this time the grating plate is thin. When the observation distance is less than 50cm, 75LPI ~ 150LPI should be selected. In addition, the selection of the number of grating lines is also affected by the size of the image format. When the image format is smaller than A5, the grating plate above 75LPI is applied, and the stereo picture produced at this time is delicate and soft.
②Viewing angle range (φ)
The angle of view refers to the maximum angle that can be allowed when forming an image or observing an image. The smaller the viewing angle, the more sensitive the image changes. Therefore, a grating plate with a small viewing angle can express the three-dimensional effect very well and delicately, while a grating plate with a large viewing angle is mainly used to express effects such as animation and transformation.
â‘¢Transmittance (Ï„)
Transmittance is used to express the transparency of the grating, which is determined by the grating material and processing technology. The higher the transmittance, the better the transparency. Since the stereoscopic image we discuss is pasted on the raster image with a grating plate, and the image is reproduced by the refraction of the raster sheet, the transparency of the raster sheet will directly affect the performance of the stereoscopic image. If the transmittance is high, the loss of information after the image information is refracted by the grating sheet will be less, and the brightness of the reproduced image will be stronger; on the contrary, if the transmittance is too low, the image information will be more refracted by the grating plate The loss, which will affect the quality and brightness of the reproduced image. Therefore, try to choose materials with high transmittance to make grating plate.
â‘£Refractive index (n)
The refractive index is determined by the grating material itself. Under certain other conditions, for a grating plate with a high refractive index, the larger the viewing angle θ1, the better the resolution.
3. How to make raster images
In general, there are three methods for making raster images: stereo photography, computer generation, and image processing software processing.
â‘ Stereo photography method Stereo photography method is a traditional raster image production method. The key to operation is to take a stereo picture, and it is necessary to accurately calculate the layout, distance, angle, center point, etc. of the subject before shooting. Divided into direct method and indirect method. The direct method is to put the cylindrical lens grating plate in front of the photosensitive film, move the camera in a certain field of view, and shoot the subject continuously; the indirect method is to take more than two photos at a specific position, and then accurately combine them into one Zhang. When the stereographic method is used to produce a raster image, the details of the image are accurately projected onto the surface of the photosensitive material through the raster. The pitch of the raster stripes and the width of the image details coincide with each other, so it is very accurate. The resulting stereo image has a better stereo effect. However, since the stereo camera method requires special equipment and is cumbersome to operate, the use range of the method is also limited, so it is rarely used now.
â‘¡Computer generation method This method is based on the production principle of raster image, using a computer to use the corresponding algorithm to cut each frame in the image sequence into vertical strip images and then alternately synthesize them in turn, and then generate them through compression processing The final raster image, this method does not require special shooting equipment, and the operation is simple. After using ordinary software such as Photoshop to perform some processing on the ordinary image, the raster image can be synthesized. Therefore, it has been widely used.
â‘¢ Image processing software processing method This method is to use image processing software such as Photoshop, and use manual operation to divide each frame in the image sequence. Then collage the required raster image. Although the principle of using this method is simple, it is more troublesome to operate and requires certain skills. Moreover, using Photoshop image processing software for image synthesis, the misalignment of the generated image details is not the actual required misalignment. Therefore, the synthesized image often has a very obvious aliasing phenomenon, which will be serious under the magnification of the raster. Affect the quality of stereo images.
By analyzing and comparing the above three raster image generation methods, we think that the computer generation method is indeed a more feasible method, so our company has developed its own three-dimensional design software based on the advantages of similar software on the market.
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