Image synthesis in stereo printing
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From the perspective of the three-dimensional printing process, the synthesis of stereo images is the most important link in stereo printing, and its effect is directly related to the quality of printed matter. There are many methods for stereoscopic image synthesis. This paper describes three typical methods of stereoscopic image synthesis.
First, traditional stereo image synthesis
1. Simultaneous methods of photography and synthesis
Stereoscopic image capture and synthesis are performed simultaneously. With a large-size stereo camera, the optical axis of the camera is surrounded by the subject while the photographing is being performed, and the grating superimposed on the photoreceptor moves in the opposite direction.
2. Optical projection synthesis method
A multi-lens stereo camera or a single-lens flat camera is equipped with a positioning guide to capture a set of plane images of the left and right scenes, and the film is then subjected to a post-optical projection method.
1 grating and photosensitive sheet relative movement projection synthesis method
2 change projection angle projection synthesis method
Second, computer stereo image synthesis
1. Three-dimensional printing image processing method by multi-view
Making a three-dimensional printed image using the left and right views is the simplest method of stereoscopic image processing, but it must be taken by a professional stereo camera or simulated by the angles of observation of the left and right eyes. Since the photograph taken in this way contains stereoscopic information, the image processing method is also relatively simple, as long as each view is divided and combined, but each image must be required to have the same size.
Usually, in order to get a better stereoscopic effect, it is generally necessary to use two or more pictures, that is, to shoot from multiple angles, so that the printed image can produce a better stereoscopic effect at different angles. According to the analysis of the imaging principle of the cylindrical lens grating plate, as long as the respective views constituting the stereoscopic image are appropriately processed, the left and right views are respectively decomposed into very thin image strips, which are placed on both sides of the optical axis of each cylindrical lens, and respectively Make the left and right eyes only see the corresponding view information.
The process of synthesizing the stereoscopic image from the multi-view is as shown in FIG. 4, and the left and right visual images are vertically stripped according to the grating plate parameters, and the same numbered bars are sequentially arranged according to the position order of the images at the time of shooting to form a new frame. The image including the stereo information is such that each image strip (A1, B1, C1 in Fig. 4) should occupy one pitch. In this way, the corresponding position information of each group of scene images is sequentially arranged at equal intervals under the same number of raster lines, and the key of the raster stripe image synthesis is the mutual matching between the numbered scene image strips.
The left and right eyes can view the image of each point through different pitch units of the grating plate, and the images composed of the units are different, but 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 the left and right eyes are also continuously changed, and the stereoscopic images formed in the brain are continuously changed accordingly, as if the eyes are directly viewing the three-dimensional realm of the real scene. This achieves the purpose of three-dimensional image display.
2. Plan view to process stereoscopic printed image
Due to the development of computer image processing technology, very complicated image processing work can be realized. Through the image processing method, not only the left and right view images can be synthesized into the same stereoscopic image as the actual scene perception, but also the unrelated arbitrary planar images can be synthesized into a pseudo stereoscopic image, that is, a virtual stereoscopic image that does not actually exist can be generated. . With this method, not only can different images be combined into one pseudo-stereoscopic image, but also different parts of a planar image can be made to have different stereoscopic effects. However, this method of image processing is more complicated than the multi-view stereoscopic image processing method, and can only have a limited number of depth of field layers, and cannot have an arbitrary depth level like a real stereo image, so it is called Pseudo perspective.
The biggest difference from the multi-view method is that the method of processing the pseudo-stereoscopic view is not to arrange the segmented image strips in the order of the left and right views, but to arrange them according to the stereoscopic vision. The left and right views are no longer arranged in the same column. Below the lens. As shown in Figure 6, the A plane is a planar image that is closer to the eye, and the B plane is a planar image that is farther from the eye. To synthesize the two images into a stereoscopic image with a near-far feeling, it is necessary to split them into On the C plane. For the near-attraction A, the images formed by the left and right eyes are respectively located on the right and left sides of the C plane (a and a1); and the far spots B, the images formed by the left and right eyes are respectively located on the right and left sides of the C plane (b and b1). When observing the C-plane image, the left-looking image enters the left eye through the cylindrical lens, and the right-looking image enters the right eye to form stereoscopic vision. Therefore, the purpose of image processing is to calculate the points in the C-plane according to the distance of the image from the eye. Project the point and calculate the coordinate position after the image of each depth of field is synthesized. The principle for processing pseudo-stereoscopic images of multiple depths of field is the same, except that the number of divided images is larger.
It is worth noting that in addition to the projection calculation of the C-plane in the near and far spots, it is also necessary to consider the occlusion of the distant objects by the close-up objects. 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.
Third, based on 3D4U stereo image synthesis
"3D4U PRINTING Special Visual Effects Design Software" is a professional comprehensive software developed by Medib Leopard. It is the only comprehensive software in the world with a full set of professional stereo and visual effects production and output. It has been widely used and recognized by three-dimensional printing industry in the world, and its image output format has gradually become the standard output format of the three-dimensional printing industry and the digital output industry.
1. Produce a real stereo image from a flat image
A sequence of stereoscopic images is typically obtained by a stereo camera system. But the images we usually have are not derived from such a special system, but a single photo taken by a general camera. Of course, we can synthesize some scenes by synthesizing scenes, and then synthesize them with different aberrations to obtain the sequence diagram. In such a composite map, the depth variation of each object itself is ignored, which is reasonable for small objects, but may not be ideal for larger objects. Since the aberration variation of each object is discontinuous and looks more jumpy, the realism of the synthesized stereogram is always not as perfect as the stereogram obtained by stereo photography. We know that a stereo image sequence is generally composed of multiple photographs taken at different parallel positions, and each single image does not differ from the image we usually take. If we know the shape of the object being shot, under certain conditions, we can calculate a stereoscopic sequence image from a simple image. 3D4U provides us with such a tool, a flat to stereo sequence image converter. We can generate a stereoscopic sequence image from an image by using scenes of known shape or scenes similar to those shapes. In the generated stereo sequence diagram, a continuously changing aberration is given, which can be directly stored in a stereo format image file MB3D or a format MBF image sequence. The former format is used for raster image editing, and the latter is used for raster image synthesis.
2. Using Photoshop with 3D4U to make a stereo view
1 First make a well-designed picture in Photoshop and save it in *.psd format. Cut out each layer, the background color of the layer should be consistent with the actual background color of the original, and save it in *.jpg format. This step is to use the mask tool quickly and conveniently in 3D4U, which can save a lot of money. The time of the manual mask.
2 Next, call 3D4U, and call out the *.jpg image just cut out in 3D4U. After each *.jpg image is produced through mask or stereo image, it should be stored in *.mbf or *.mb3d format. The final stereo image can be rendered in the Raster Image Editor.
3 For which image to use *.mbf format, which use *.mb3d, we need to see the shape of the image content. For example, in order to reflect the stereoscopic effect of the near and far, the beach is adjusted by the raster image → tool → stereo image formation. The file format after storage is *.mbf format.
4 You can look at the preview. Since the image number 12 was used in the stereo image forming option, the maximum number of pictures is adjusted to 12 in the raster synthesizer, which becomes a 12-frame animation. Now you can feel the stereo effect of the image. Plane characters and flowers can be stored directly in the *.mbf format after masking. Press shift to easily view the final mask effect.
5 After all the pictures are stored, you can start raster image editing. Open the raster image editor, adjust the size, adjust the unit in File → Parameter Settings → General Items, load all the pictures, and adjust the picture level. Adjust the aberration after loading, save it after previewing.
6 Make a raster image. Since the maximum number of pictures is 12, it is rendered 12 times. Open the file → parameter setting → custom, such as 24 line imported 2mm grating, the output is calculated as 24 lines × 12 frames = 288 / inch, with 300dpi. Click on the vertical raster to create a raster image → adjust the output size and click OK.
7 Finally, you can generate a preview and make a small animated GIF effect. After reading the final effect of the grating plate, it can be printed.
Fourth, the conclusion
The above three image synthesis methods are widely used in stereo printing, so they are relatively core and typical in the stereo image synthesis method. With the development of computer image synthesis technology, the stereo image synthesis method will be more mature, and stereoscopic printing will have greater development.