JPH0628489A - Image processor and image data generating method in surface display - Google Patents

Abstract

PURPOSE:To maintain almost the same processing time as before, and also, to improve the picture quality of a distance image (surface image). CONSTITUTION:In an image processing processor, first of all, ray tracing is executed until it hits against an object by a first ray RY1 of a first pitch P1 set to the same as pixel size of three-dimensional voxel data. When it hits against the object, it returns to a start point A at the time of final ray tracing by a first ray RY1, and from its start point A, ray tracing is continued until it hits against the object again by a second ray RY2 of a second pitch P2 (smaller than a first pitch P1). A distance extending from the projection surface to the object surface is calculated from the sum of products of the ray pitch and the number of times of tracing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface display image processing apparatus for displaying the surface shape of an object such as bone, epidermis, and tumor, and an image data creating method, and more particularly to implementing a ray tracing method. An apparatus and a method.

[0002]

2. Description of the Related Art Conventionally, a ray tracing method is known as one of methods for creating a surface image of an object based on three-dimensional voxel data of the object. In this ray tracing method, as shown in FIG. 6, a ray RY having a constant pitch (length) from a virtual projection plane (or toward this projection plane) hits (collides with) a voxel corresponding to an object. Trace (skip) up to. By this tracing, when the ray RY hits the relevant voxel, the product of the number of times the ray RY has been traced and the pitch of the ray RY is calculated to obtain the distance from the virtual surface to the object.
Then, a distance image (depth image) in which the distance is the pixel value
Was calculated, and the surface image was created by shading this range image. At this time, the pitch of the ray RY is usually set to the same value as the pixel size of the three-dimensional voxel.

[0003]

However, in the conventional ray tracing method, if the pitch of the rays is made finer in order to obtain a more accurate surface distance image,
Since the number of ray traces (the number of repetitions) increases, the processing time for creating image data becomes longer. On the contrary, if the ray pitch is increased to reduce the processing time, the , The difference between the ray end point (tip) position and the object plane, that is, the error (FIG. 6).
However, there is a contradictory problem that the image quality deteriorates.

The present invention has been made in view of the problem of the conventional ray tracing method, and an object thereof is to significantly improve the image quality even when the processing time is almost the same as the conventional one.

[0005]

In order to achieve the above object, an image processing apparatus according to the present invention, as shown in FIG.
First ray tracing means for sequentially tracing rays of the first pitch in the projection direction with respect to the three-dimensional voxel data, and whether or not the ray of the first pitch hits a voxel having a pixel value representing an object. Hit judgment means to judge whether,
When the hit judging means judges that the ray has hit, the pitch changing means for changing the pitch of the ray to the second pitch finer than the first pitch, and the pitch changing means for changing the pitch Based on the second ray tracing means for tracing the ray to the boundary surface of the voxel corresponding to the object at a pitch of 2, and the number of tracings and the respective pitches of the rays traced by the first and second ray tracing means. And a distance calculation means for calculating the distance to the projection surface.

Further, according to the image data creating method for surface display of the present invention, the ray having the first pitch is sequentially traced in the projection direction with respect to the three-dimensional voxel data, and the voxels having the pixel value representing the object are described above. When it is determined that the ray has hit, and when it is determined that the ray has hit, the pitch of the ray is changed to a second pitch finer than the first pitch, and then the changed second The ray is traced to the boundary surface of the voxel corresponding to the object at a pitch of, and thereafter, the distance to the projection surface is calculated based on the number of times of tracing the ray traced by the first and second pitches and each pitch. It was characterized by doing.

[0007]

According to the image processing apparatus of the present invention, the first ray tracing means sequentially traces the rays of the first pitch with respect to the three-dimensional voxel data in the projection direction, and in parallel with this tracing. The hit determination means determines whether or not the ray having the first pitch hits a voxel having a pixel value representing an object. When it is judged by the hit judging means that the ray has hit, the pitch changing means changes the pitch of the ray to a second pitch which is finer than the first pitch. This time, the ray is traced by the second ray trace means to the surface of the voxel corresponding to the object with the changed second pitch. Then, in the distance calculation means, the distance to the projection surface is calculated on the basis of the number of times of tracing each ray traced by the first and second ray tracing means and each pitch.

Further, according to the image data creating method for surface display of the present invention, the ray of the first pitch is sequentially traced in the projection direction with respect to the three-dimensional voxel data group. In the meantime, it is determined whether or not a ray hits a voxel having a pixel value representing an object, and when it is determined that the ray has hit, the pitch of the ray is smaller than the first pitch.
Is changed to the pitch. After that, the ray is traced to the surface of the voxel corresponding to the object at the changed second pitch, and the ray is traced at the first and second pitches. The distance is calculated.

As described above, the ray is traced at a large pitch until it hits the surface of the object, and once it is hit, it is traced again at the fine pitch to the surface of the object.
As a result, as the processing time, since only the ray trace by the fine pitch increases, it is almost the same as the case of the ray trace by the conventional constant pitch, and at the same time,
The precision of the distance data calculation is improved and the image quality is improved due to the ray trace of fine adjustment with a fine pitch.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

The image processing apparatus shown in FIG. 2 comprises a central processing unit (hereinafter referred to as CPU) 1 for controlling the entire apparatus. An image disk 2 storing image data is connected to the CPU 1 via a bus structure, and an input device 3, a display device 4, and a general-purpose memory 5 are connected via a bus structure.

The image disk 2 stores medical image data of the inside of the subject obtained by modalities such as an X-ray diagnostic apparatus, an ultrasonic diagnostic apparatus, and a magnetic resonance imaging apparatus. The input device 3 has a mouse, a keyboard, a touch panel, and the like. The display device 4 has a CRT display and a circuit for displaying the supplied digital image data on the CRT display.

Further, in the bus structure connected to the CPU 1,
The image processor 6 and the screen memory 7 are connected. The image processor 6 receives a command from the CPU 1 and executes a process relating to a ray trace described later. Further, the general-purpose memory 5 stores in advance a system control main program and a sub-program shown in FIG. 3 described later.

Next, the contents of the subprogram shown in FIG. 3 will be described together with the operation of the embodiment. When the operator inputs information indicating that the user wants to display the front surface from the input device 3 and the position data of the projection surface necessary for the front surface display, C
The PU 1 instructs the image processor 6 to perform the surface display process.

The image processor 6 includes an image disk 2
For example, the CT image data of consecutive slices stored in is read out, the target region is extracted for each slice, and binary data is accumulated in the slice direction while performing interpolation between slices, if necessary, three-dimensional voxel data. To create. Then, based on the input information of the operator, after assuming a projection plane perpendicular to the set sight line (ray) direction, the process shown in FIG. 3 is started. It should be noted that this subprogram is to be processed in parallel corresponding to each pixel on the projection surface, based on the time sharing processing or the like.

The processing of FIG. 3 will be described. In step 10 of FIG. 3, the image processor 6 reads the value of the normal pitch P ₁ (corresponding to the first pitch of the invention) of the ray from the general-purpose memory 5 to the work area of the processor. This normal pitch P ₁ is set to the same value as the pixel size of the three-dimensional voxel here. Then, the processor 6 shifts the processing to step 11, advances the read ray RY _{1 according} to the read normal pitch P ₁ by _one from the given initial position in the projection direction (viewing direction) (see FIG. 4). ), And the number of traces N ₁ is stored.

Next, in step 12, the processor 6 hits (reaches) a voxel having a pixel value (logical value "1") whose ray trace end position, that is, the tip position, corresponds to an object such as a bone. Yes) or not. In this determination, the pixel value at the ray tip position is the logical value "0".
And if you haven't hit the object yet,
The process of step 13 is performed. In step 13, it is determined whether or not the ray tracing is completed, for example, by checking whether or not the ray tip position is already outside the predetermined area.

When it is determined in step 13 that the ray trace is to be continued, the processing of steps 11 and 12 is repeated. As a result, the ray RY ₁ having the normal pitch P ₁ is advanced in the projection direction one after another, with the end point position (tip position) of the previous ray as the start point position. On the contrary, when it is determined in step 13 that the ray tracing is to be ended, for example, the ray RY ₁ has been advanced many times, but the target object has not been hit and the object has gone out of the predetermined area. At this time,
End ray tracing.

On the other hand, if it is determined in step 12 that the object is hit (YES), then step 1
The processes 4 to 17 are sequentially performed. Of these, step 1
In 4, the ray pitch is the second pitch P ₂ (for example, 3 which is smaller than the normal pitch (first pitch) P ₁ until now).
Pitch width of 1/10 of the pixel size of the dimension voxel:
<P ₁ ). In step 15, the second
The trace direction of the second ray RY ₂ depending on the pitch P ₂ is read. This trace direction is predetermined,
In this embodiment, as shown in FIG. 4, the starting point A of the first ray RY ₁ at the time of the final trace is set as a takeover point, and the trace is made from this takeover point A toward the object surface in the forward direction (the same as the projection direction). is there.

Therefore, in step 16, the image processor 6 continuously traces the second ray RY ₂ having a finer pitch than that in the previous stage from the takeover point A relating to the first ray RY ₁ in the projection direction. At the same time, the number N ₂ of traces is stored. Next, at step 17, it is judged from the pixel value whether the second ray RY ₂ hits (reaches) the boundary surface of the object, and if not hitting, the processing of step 16 is repeated. This allows the second
Rays RY _{2 of} are advanced in the projection direction one after another. And
If it is judged in step 16 that there is a hit,
The processing moves to step 18.

In step 18, the data stored by the ray tracing so far, that is, the first ray R
The pitch P _{1 of} Y _1, the number of traces N _1, and the second ray R
Based on the pitch P _{2 of} Y ₂ and the number of traces N ₂ ,
“P ₁ · N ₁ + P ₂ · N ₂ ” is calculated to obtain the distance from the projection plane to the object plane.

The processing of steps 10 and 11 in FIG. 3 constitutes the first ray tracing means of the invention, the processing of step 12 in the figure constitutes hit determining means of the invention, and the processing of step 14 in the figure is It constitutes the pitch changing means of the invention. Further, the processing of steps 15 to 17 in FIG.
Ray tracing means, and the processing of step 17 in the figure constitutes the distance calculating means of the invention.

As described above, according to this embodiment, ray tracing is performed at the coarse pitch P ₁ similar to the conventional one until the object is hit (see the range D1 in FIG. 4), and after hitting the object. Ray trace is performed at a fine pitch P ₂ (see FIG. 4).
Range D2). Then, the object from the projection plane by the sum of the distance D3 measured by coarse pitch P ₁ from the projection plane to take-over point A, and the distance D2 measured by the fine pitch P ₂ from the takeover point A to the boundary surface of the object The distance D4 to the surface is obtained, and a distance image is created based on this distance D4.

For this reason, the ray tracing for fine adjustment by the fine pitch P ₂ is suppressed to the minimum, and the ray tracing processing time is slightly increased compared with the case of ray tracing only with the coarse pitch. Time does not increase significantly. Moreover, since the precision of distance measurement is improved by the fine trace of the fine adjustment, there is an advantage that the image quality of the distance image is significantly improved.

Further, when it is necessary to calculate the distance with a certain accuracy, conventionally, it was necessary to perform ray tracing from the beginning at a pitch corresponding to the accuracy, but in this embodiment,
Since the ray trace can be performed at a pitch larger than the pitch until the object is hit, the given accuracy can be maintained and the ray trace processing time can be shortened as a whole.

It should be noted that in the above-described embodiment, the ray trace for fine adjustment by the second ray RY _{2 having} the fine pitch P ₂ is performed in the forward direction, but this may be reversed. That is, as shown in FIG. 5, the position of the end point (tip point) at the time of the last ray tracing due to the coarse pitch P ₁ is taken as the takeover point B, and from this takeover point B, the direction opposite to the projection direction (reverse direction). Alternatively, ray tracing may be performed until the object goes out. That is, in the example of FIG. 5, “distance D3 = D1-D
2 ". Also, the direction of the ray trace for the finer pitch can be used properly.

[0027]

As described above, according to the image processing apparatus and the image data creating method for front surface display according to the present invention, the coarse pitch (first pitch) similar to the conventional one is provided until the object is hit. Raytrace with, and after hitting the object, raytrace with a fine pitch (second pitch), and calculate the distance from the projection surface to the object plane based on each pitch and the number of traces of both raytraces. Therefore, the ray trace with a fine pitch is minimized, and the distance can be accurately measured with almost no increase in the ray trace processing time, that is, the image processing time of the surface display compared with the conventional single pitch. Well calculated,
The image quality of the range image (surface image) can be improved significantly as compared with the conventional one.

Further, when it is necessary to calculate a distance with a certain accuracy, in other words, when it is necessary to obtain a distance image with a certain accuracy, by applying the present invention, the accuracy can be maintained and the conventional method can be used. The processing time can be shortened more than that.

[Brief description of drawings]

FIG. 1 is a claim correspondence diagram showing a basic configuration of a claim of an image processing apparatus according to the present invention.

FIG. 2 is a block diagram showing a configuration example of an embodiment of an image processing apparatus according to the present invention.

FIG. 3 is a flowchart showing a processing procedure related to ray tracing.

FIG. 4 is an explanatory diagram showing ray tracing according to the embodiment.

FIG. 5 is an explanatory diagram showing ray tracing according to a modified example.

FIG. 6 is an explanatory diagram showing a conventional ray trace.

[Explanation of symbols]

 1 CPU 2 Image Disk 3 Input Device 5 General-purpose Memory 6 Image Processor 7 Screen Memory

Claims (4)

[Claims] 1. A first ray tracing means for sequentially tracing rays of a first pitch in a projection direction with respect to three-dimensional voxel data, and voxels having pixel values in which the rays of the first pitch represent an object. Hit determining means for determining whether or not a hit has been made, and when the hit determining means determines that the ray has hit, the pitch of the ray is changed to a second pitch finer than the first pitch. Pitch changing means, second ray tracing means for tracing rays to the boundary surface of voxels corresponding to the object at the second pitch changed by the pitch changing means, and the first and second ray tracing means. An image processing apparatus comprising: a distance calculation unit that calculates a distance to a projection surface based on each number of traces and each pitch of the ray traced by. 2. The second ray tracing means comprises the second ray tracing means.
2. The image processing apparatus according to claim 1, which is a means for tracing in a forward direction the ray having the pitch of 1 to the starting point of the ray having the last trace of the first pitch to the boundary surface of the voxel corresponding to the object. 3. The second ray tracing means comprises the second ray tracing means.
2. The image processing apparatus according to claim 1, which is a means for tracing the ray of the pitch of 1) in the reverse direction from the end point of the ray of the 1st pitch traced last to the boundary surface of the voxel corresponding to the object. 4. The ray having the first pitch is sequentially traced in the projection direction with respect to the three-dimensional voxel data, and it is determined whether or not the ray has hit a voxel having a pixel value representing an object. When it is determined that the ray has hit, the pitch of the ray is changed to a second pitch finer than the first pitch, and then the boundary surface of the voxel corresponding to the object at the changed second pitch. Trace the ray up to
Thereafter, a method for creating image data in surface display is characterized in that the distance to the projection surface is calculated based on each number of times of tracing the rays traced by the first and second pitches and each pitch.