JPH0785268B2 - Method and device for displaying three-dimensional image - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for displaying a three-dimensional image, and more particularly to a method and apparatus for displaying a three-dimensional image according to the density gradient of each point of the image. . Displaying medical images by a computer is
The conventional two-dimensional display method has been developed into a three-dimensional display method. For example, "isotope news" (I soto
pe News) (December 1985 issue, published by Japan Isotope Association), "3D display of medical images by computer" (pages 8-9). This conventional example discloses that there are a surface method and a voxel method as surface disclosure methods. In the surface method, the density is given in correspondence with the inclination angle of each point of the image, and the density is displayed on the screen to express the shadow. In the voxel method, a density is given according to a depth distance from a viewpoint or a light source to each point on the image, and this density is displayed on a screen to express a shadow. Although the voxel method is excellent in grasping the depth distance, the voxel method is superior to the surface method in comparison with the surface method.
It has a drawback that the shape of a fine part is not accurately grasped. on the other hand,
In the surface method, the shape of a fine portion can be accurately grasped, but the depth distance is not accurately grasped. Shading in the three-dimensional display of an image can be realized by using either one of the voxel method and the surface method, but in order to bring out the features of each,
It is preferable to use the image according to the position and shape of the image or the point of interest. Therefore, when displaying one screen, it is necessary to consider that one is the voxel method and the other is the surface method. However, both the voxel method and the surface method have the above-mentioned drawbacks. Therefore, the pure voxel method,
The pure surface method cannot achieve shading under a more accurate three-dimensional display. It is an object of the present invention to provide a three-dimensional display method and apparatus which enables correction of density data obtained by the voxel method by the surface method to enable more accurate shading. According to the present invention, the corrected density is obtained by adding the density obtained by the voxel method at each point by adding the density gradient of the density of the neighboring pixels to obtain the corrected density. The corrected density is displayed on the display surface. According to the configuration of the present invention, the corrected density data is calculated for each point and the three-dimensional shade display is performed. FIG. 1 shows an embodiment of a processing apparatus to which the present invention is applied.
Shown in. The computer (CPU) 201 is the center of the processing device. High-speed dedicated hardware (correction density calculation device) 20
In step 2, the correction density data, which is the center of the process of the present invention, is calculated. The disk or drum memory 203 is a large capacity memory and stores data before processing and data after processing. The display device 204 is, for example, a CRT display device,
3D display. The above devices 201 to 204 are connected by a common bus 205. The three-dimensional display target data may be CT image data or projection data. For example, an example of CT slice three-dimensional display will be described with reference to FIG. CT for the subject
The apparatus acquires a plurality of CT images # 1, # 2, # 3, .... For example, the maximum number of human heads is about 100. By stacking a plurality of CT slice images thus obtained, a three-dimensional image is obtained. There is a three-dimensional display method as this three-dimensional image display method. The three-dimensional display method is a method of producing an apparent three-dimensional image mainly by computer graphic technology and projecting and displaying this on a normal two-dimensional display. The three-dimensional display method includes a cross-section conversion display method and a surface display method. The cross-section conversion display method is a method of displaying a human body image collected as a three-dimensional data structure, that is, a three-dimensional image on an image memory, cutting it from any direction, and reproducing and displaying the cut surface as a two-dimensional image. Yes, the basic is high-speed interpolation calculation of the gray value corresponding to the coordinates. There is a surface display method as a surface display method for the cut surface obtained by the cross-section conversion display method, or as a method for properly displaying the surface of the image itself regardless of the cut surface. This surface display method is a method for forming a three-dimensional image of the surface shape of an intricately complicated organ, bone or the like. Typical surface display methods include the surface method and the voxel method. The two methods have been described above. The voxel method is also called a painting algorithm method. First, it is assumed that the disk memory 203 stores three-dimensional voxel images obtained by the voxel method arranged for three-dimensional display. The computer 201 is used to obtain a voxel image from the original image by the voxel method. The computer 201 sequentially extracts the pixel density data of the original image stored in the disk memory 203 and performs the voxel method to obtain three-dimensional voxel pixel density data. The three-dimensional voxel pixel density data is stored in the disk memory 203 again. The situation is shown in FIG. A state in which the voxel pixel density data A _ij is stored for each pixel is shown. Note that n indicates the size of the screen or the size of the screen to be processed by the voxel method. The corrected density data according to the present invention is the value B _ij calculated by the density gradient near the voxel pixel position (i, j). The corrected density data B _ij is replaced in place of the voxel pixel density A _ij . Since the corrected density data B _ij is the value obtained from the density gradient, it is the density itself corrected by the surface method. This calculation work is performed by the high-speed dedicated hardware 202. The procedure is shown in FIG. FIG. 4 shows an explanatory diagram thereof. The data before processing is the voxel pixel density data shown in FIG. 2, and this data may remain stored in the disk memory 203, or may be brought to another high-speed memory. Good. In the following, it is assumed that the processing is performed by the high-speed dedicated hardware after the transfer to the high-speed memory. In FIG. 3, steps 10 and 100 are processes by the computer 201, and steps 20 to 90 are processes by the high-speed dedicated hardware 202. Further, FIG. 4 shows a state in which the display example based on the voxel pixel density data is converted into the display example based on the corrected density data. The original image is a voxel image. Density correction by neighboring pixels is performed for all pixels of this original image. In FIG. 4, when the density of a scanning pixel is A, it is one pixel in the peripheral two-axis direction through the scanning pixel.
An example in which the density A is corrected to the density B by the pixels A ₁ , A ₂ , A ₃ , and A ₄ at the points is shown. This correction is performed for all n × n pixels. The processing procedure will be described in detail with reference to FIG.
In step 10, the original image data in the disk memory 203 is transferred to the main memory (not shown) in the computer 201. After this movement, the computer 201 executes processing on the dedicated hardware 2
Leave it to 02. First, the dedicated hardware 202 initializes the access address of the original image in steps 20 and 30. If the access method based on the raster scan method is adopted, it means that the access method is based on (x ₁ , y ₁ ) in FIG. For this (x ₁ , y ₁ ), neighboring pixels are extracted as shown in FIG. 4 (b) (step 40). In the figure, the density by (x ₁ , y ₁ ) is A, and the pixel densities on both sides x ₁ −1 and x ₁ +1 in the x direction are A ₂ , A ₄ , and y ₁ −1, y in the y direction. The pixel densities of ₁ +1 are A ₁ and A ₃ . The inclination of the pixel density of the four points (A ₂ -A _4), taking into account the (A ₁ -A _3), to obtain a corrected density data B at (x _1, y ₁₎ (step 40). The general formula for calculating the corrected density data B is as follows. [Equation 1] δ is a constant determined by the reflection state of the original object from which the image was obtained. δ = 1 for a non-reflector and δ> for a reflector.
It becomes 1. Therefore, the closer to the mirror surface, the larger the value of δ. For example, it is usual to set δ = 1.5 to 2.0 for metal, δ = 1 for gypsum, and δ = 1 for human body (however, δ may be changed depending on bone and skin). Angle θ ₁
Is an inclined line with respect to the x-axis (a straight line connecting A ₂ and A ₄ )
The angle of inclination, θ ₂ is the inclination line (A ₁ and A ₃
It is the angle of inclination of the straight line that connects with). cos θ
₁ indicates a component of the angle θ ₁ parallel to the x-axis, and cos θ ₂ indicates a component parallel to the y-axis. On the other hand, the equation (1) can be replaced with the following equation in the neighborhood four-point method as shown in FIG. [Equation 2] Here, K represents a contrast constant, and G represents a distance per unit density. For example, K = n and G = 1. Thus, B obtained by the equation (1) or (2)
Is the corrected density corrected by the surface method at (x ₁ , y ₁ ) and replaces the density A obtained by the voxel method (step 50). In step 60, x _{1 is set} to (x ₁ +1) and one point of interest is moved to the right.
Check if it has reached _max . In step 80, y _{1 is set} to (y ₁ +1) to move one point downward, and in step 90, it is checked whether or not y _max is reached. These steps 60 to 90 merely show scanning by the raster scanning method. Step 100 is processing by the computer 201, which stores the result and displays it on the display device 204.
Results are shown in FIG. This storage may be finally stored in the disk memory 203, and in the case of display, it is stored in the refresh memory and then displayed. In the embodiment, the peripheral point is set for each point. However, if the peripheral point is set for every two points, the peripheral point for every three points, etc., the inclination of the surrounding point can be accurately detected, and more accurate correction can be made. Although the method of correcting the pixel density data of the voxel method has been adopted, both the density data of the voxel method and the corrected density data may be used. In that case, the density data of the voxel method may be left as it is, and the modified density data may be calculated based on the density data of the voxel method and stored together in the memory. Further, although the inclinations are separate in the x and y directions, they may be entangled and corrected. Further, it can be realized by an arithmetic unit processed by a microprogram instead of the high-speed dedicated hardware. According to the present invention, the pixel density data by the voxel method can be corrected by the surface method.

[Brief description of drawings] FIG. 1 is a diagram illustrating an embodiment of the present invention. FIG. 2 is an example diagram of concentration data of the voxel method. FIG. 3 is a diagram showing a processing procedure of the present invention. FIG. 4 is an explanatory diagram of an image example. FIG. 5 is a diagram showing an example of corrected density data. FIG. 6 is an explanatory diagram of a three-dimensional display image. [Explanation of symbols] 201 Computer (CPU) 202 High-speed dedicated hardware 203 disk memory 204 display device

Claims (1)

Claims: 1. A gradient of voxel pixel density in the vicinity of each voxel pixel in a three-dimensional voxel image stored in a memory is calculated,
A method for displaying a three-dimensional image, in which a corrected density corrected by the surface method is calculated from the inclination for each pixel and a three-dimensional image having the corrected density is displayed on a display means. [2] A memory for storing a three-dimensional voxel image, a processing means for obtaining a corrected density corrected by the surface method from each voxel pixel density of the three-dimensional voxel image, and a display for displaying the three-dimensional image of the corrected density In addition to the above, the processing means obtains the gradient of the voxel pixel density in the vicinity of the voxel pixel for each pixel, and the pixel density calculated for each pixel from this gradient is used as the corrected density corrected by the surface method. Display device for 3D images.