From the perspective of the process flow of three-dimensional printing, the synthesis of three-dimensional images is the most important link in three-dimensional printing, and its effect is directly related to the quality of the printed matter. There are many methods for stereo image synthesis. This article describes three typical stereo image synthesis methods.
1. Traditional stereo image synthesis
1. Method of simultaneous photography and synthesis
The shooting and synthesis of the stereoscopic image are carried out at the same time. With a stereoscopic camera with a large film, the optical axis of the camera is centered on the subject as the axis is taken. At the same time, the grating superimposed on the photosensitive film moves in the opposite direction.
2. Optical projection synthesis method
Use a multi-lens stereo camera or a single-lens plane camera with a positioning guide to shoot a set of plane images of left and right scenes, and the negative film then undergoes a post-optical projection synthesis method.
â‘ Relative movement projection synthesis method of grating and photosensitive sheet
â‘¡ Change the projection angle projection synthesis method
2. Computer stereo image synthesis
1. Three-dimensional printing image processing method from multi-view
It is the simplest stereoscopic image processing method to create a stereoscopic printed image using left and right views, but it must be photographed by a professional stereo camera or simulated by the observation angle of the left and right eyes. Since the photos taken in this way contain stereoscopic information, the image processing method is relatively simple, as long as the views are divided and combined, but each image must be the same size.
Generally, in order to obtain a better stereoscopic effect, it is generally necessary to use more than two pictures, that is, shooting from multiple angles, so that the printed image can produce a better stereoscopic effect when viewed at different angles. According to the analysis of the imaging principle of the cylindrical lens grating plate, as long as the views constituting the stereoscopic image are properly processed, the left and right views are decomposed into very thin image strips, and placed on both sides of the optical axis of each cylindrical lens, you can separate Make the left and right eyes only see the corresponding view information.
The process of synthesizing a stereoscopic image from multi-views is shown in Figure 4. The left and right visual images are divided and numbered in the longitudinal stripe according to the parameters of the grating plate, and then the same numbered strips are arranged in order according to the position of the image at the time of shooting to form a new The image that contains the stereo information, so that each image strip (as shown in Figure 4 A1, B1, C1) should occupy a full pitch. In this way, under the same raster line number, the corresponding position information of each set of scene images is arranged at equal intervals in sequence. The key to the synthesis of the raster stripe image is the matching between the numbered scene image strips.
The left and right eyes can see the image of each scene through different grating units of the grating plate. Although the images composed of each unit are different, they can be synthesized in the brain to form a stereo image. When the viewer makes any continuous movement on the same horizontal plane, the combined images viewed by his left and right eyes also continuously change, and the stereoscopic image formed in the brain also changes accordingly, as if his eyes directly watch the three-dimensional realm of the real scene. This achieves the purpose of three-dimensional image display.
2. Processing method of making stereoscopic printing image in plan view
Due to the development of computer image processing technology, very complex image processing work can be achieved. Through the image processing method, not only can the left and right view images be synthesized into a stereo image with the same feeling as observing the actual scene, but also any unrelated plane images can be synthesized into a pseudo stereo image, that is, a virtual stereo image that does not actually exist is generated . With this method, not only can different images be synthesized into a pseudo stereo image, but also different parts of a plane image can be made into a stereo effect with different distance perception. However, this image processing method is more complicated than the multi-view stereo printing image processing method, and can only have a limited number of depth levels, and cannot have any depth level like the real stereo image, so it is called Pseudo stereogram.
The biggest difference with the multi-view processing method is that this method of processing pseudo-stereoscopic views is not to arrange the divided image strips at the same time in the order of left and right views, but to arrange them according to the imaging rule of stereo vision. The left and right views are no longer arranged in the same column Under the lens. As shown in Figure 6, plane A is a plane image closer to the eyes, and plane B is a plane image farther from the eyes. To synthesize these two images into a stereoscopic image with a sense of distance, it is necessary to divide them into C plane. For the near spot A, the images formed by the left and right eyes are respectively located on the right and left of the C plane (a and a1); while for the far spot B, the images formed by the left and right eyes are located on the right and left of the C plane (b and b1), respectively. When observing the C-plane image, the left vision image enters the left eye and the right vision image enters the right eye through the cylindrical lens to form a stereoscopic vision. Therefore, the purpose of image processing is to calculate the points on the C plane according to the distance of the image from the eye Projection point, and calculate the coordinate position of each depth of field image after synthesis. The principle for processing pseudo-stereoscopic images with multiple depths of field is the same, except that the greater the number of divided images.
It is worth noting that, in addition to the projection calculation of the near and far points in the C plane, the occlusion of the distant objects by the near objects must also be considered. If the different occlusion effects of the left and right eyes are calculated when the occlusion is processed, a better stereoscopic effect can be obtained. [next]
3. 3D4U-based stereo image synthesis
"3D4UPRINTING special visual effect design software" is a professional comprehensive software developed by Medico, and is the only comprehensive software in the world that has a full set of professional stereo and visual effects production and output. Now it has been widely used and affirmed by the 3D printing industry in the world, and its image output format has gradually become the standard output format of the 3D printing industry and the digital output industry.
1. Produce a real stereo image from a flat image
A stereo image sequence can generally be obtained by a stereo camera system. But the images we usually have are not obtained by such a special system, but single photos taken by a general camera. Of course, we can segment some scenes by synthesizing scenes, and then synthesize them with different aberrations to obtain sequence diagrams. In such a composite picture, the depth change of each object itself is ignored, which is more reasonable for small objects, but may be less ideal for larger objects. Because the aberration change of each object is discontinuous, it seems that the jump is relatively large, so the realism of the synthesized stereoscopic image is always not as natural and perfect as the stereoscopic image obtained by stereo photography. We know that a stereoscopic image sequence is generally composed of multiple photos taken at different parallel positions, and each single image is no different from the image we usually take. If we know the shape of the photographed object, under certain conditions, we can calculate a stereo sequence image from a simple image. 3D4U provides us with such a tool, flat to stereo sequence image converter. We can generate a three-dimensional sequence image from an image of scenes with known shapes or scenes similar to these shapes. In the generated stereo sequence diagram, a continuously changing aberration is given, which can be directly stored in a stereo format picture file MB3D or an image sequence in format MBF. The former format is used for raster image editing, and the latter format is used for raster image synthesis.
2. Use Photoshop with 3D4U to produce stereoscopic images
â‘ First make the designed picture in Photoshop and save it in * .psd format. Cut and extract each layer. The background color of the layer should be basically the same as the actual background color. Save it in * .jpg format. This step is to use the mask tool quickly and conveniently in 3D4U, which can greatly save Time for manual masking.
â‘¡ Next call 3D4U, call up the * .jpg image just cut and extracted in 3D4U, and each * .jpg image must be stored in * .mbf or * .mb3d format after being masked or stereo imaged, Only then can the final stereoscopic image be rendered in the raster image editor.
③For which picture to use * .mbf format and which to use * .mb3d, we need to see the shape of the picture content. For example, in order to reflect the three-dimensional effect of the near, far, and far, the beach must use the adjustment of raster image → tool → stereoscopic image formation. The file format after storage is * .mbf format.
â‘£ You can take a look at the preview. Since the number of images used in the stereoscopic image formation option was just 12, the maximum number of pictures in the raster synthesizer was adjusted to 12, which became a 12-frame animation. Now you can feel the three-dimensional effect of the image. Flat characters and flowers can be stored directly in the * .mbf format after the mask, and you can easily watch the final mask effect by pressing shift.
⑤After all the pictures are stored, you can start raster picture editing. Open the raster image editor, adjust the size, adjust the unit in File → Parameter Settings → General, load all pictures, and adjust each picture level. Adjust the aberration after loading, and save it after previewing.
⑥ Make raster images. Since the maximum number of pictures is 12, it needs to be rendered 12 times. Open the file → parameter setting → customization, for example, 24 lines imported 2mm raster, the output is calculated as 24 lines × 12 frames = 288 / inch, 300dpi is enough. Click the vertical raster to make a raster image → adjust the output size, click OK and other results.
⑦ Finally, you can generate a preview and make a GIF animation to see the effect. After reapplying the grating board to see the final effect, you can print it.
4. Conclusion
The above three image synthesis methods are widely used in stereo printing, so they are the core and typical of the stereo image synthesis methods. With the development of computer image synthesis technology, stereoscopic image synthesis methods will become more mature, and stereoscopic printing will have greater development accordingly.
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