JPH0772915B2 - Graphic shading device - Google Patents

Description

The present invention relates to an apparatus for displaying a three-dimensional curved surface on a CRT screen or the like by shading it on a CRT screen or the like using a computer. The present invention relates to a graphic shading device suitable for executing processing at high speed.

[Background of the Invention]

Use a computer to display a 3D curved surface (spherical surface or spline curved surface) described by a 2D equation or a cubic equation on a CRT screen, etc., on the curved surface geometry, light reflection characteristics of the curved surface, light source position, light source intensity, and viewpoint position. There is known a figure shading device which makes a display corresponding to a real object photographed by a television camera by changing the density. At this time, if the brightness of each point on the curved surface is calculated directly from the equation of the curved surface, the amount of calculation is very large. Therefore, in general, many sample points are taken on the curved surface, and the data at that point A means for approximating the brightness is used. The method of displaying a curved surface from the data of sample points is Folly (JDFol
y) et al., “Fundamentals of Interactive Computer Graphics (Fundamentals)
of Interactive Computer Graphics) ", Addison
Wes Lee Publishing Company (Addison
As described in Wesely Publishing Company), pp. 580-584, consider a polyhedron created by sample points, calculate the average brightness of each surface that constitutes the polyhedron, and display each surface uniformly at that brightness. Polynomial display method (Constant Shading) The brightness at each sample point is calculated from the data of the surface orientation (normal vector) at each sample point, and the brightness at other points is proportionally distributed according to the distance from each sample point ( Luminance interpolation method (Intensity Interpolation Shading or Gouraud Shading) obtained from the luminance at the sample point by linear interpolation) The normal interpolation method (Normal-vector Interpolation)
polation Shading). Generally, when the same data is obtained for sample points on a curved surface, the curved surface display accuracy improves in the order of ,,, and a more curved surface-like display can be obtained. However, the calculation amount increases in this order, and the processing takes time, and a complicated device is required for speeding up. For example, Japanese Patent Publication No. 57-57715 and "Gray Figure Generator" and Japanese Patent Application Laid-Open No. 61-70666 and "Graphic Shading Apparatus", respectively, are known as figure shading apparatuses for executing the above methods at high speed. is there.

[Problems to be solved by the invention]

However, even if the number of displayed figures increases, the processing takes time, and the waiting time of the operator until the display ends becomes long. Although the work efficiency is poor, the operator's waiting is frustrating and the operator's mental burden becomes heavy. In order to eliminate the annoyance caused by the waiting of the operator and improve the work efficiency, a further graphic shading device is required.

An object of the present invention is to solve the above-mentioned problems of the prior art by executing high-speed luminance calculation by a linear interpolation method and a normal interpolation method for a three-dimensional object figure to be displayed, and displaying based on the shaded luminance. It is an object of the present invention to provide a figure shading device capable of displaying a figure of a three-dimensional object on the means.

[Means for solving problems]

In order to achieve the above object, the present invention provides a graphic shading device for displaying a three-dimensional graphic on a display means, calculating the brightness of each dot on the display graphic, performing shading, and storing the result in a memory. Luminance linear interpolation means for calculating each of the ambient light reflection component and the diffuse reflection component of the luminance of each of the dots by the luminance linear interpolation method based on each of the ambient light reflection component and the diffuse reflection component of the luminance of the sample point; Normal interpolation means for calculating the specular reflection component of the brightness by the normal interpolation method based on the normal vector of the sample point, and obtaining the average value of the brightness of the sample point, and assigning it to the dot Brightness average value calculating means for calculating brightness, flatness determining means for determining whether the figure to which the dot belongs can be regarded as a plane, and the plane When the determination means determines that the figure can be regarded as a plane, the brightness of the dots output from the brightness average value calculation means is selected, and when the flatness determination means determines that the figure cannot be regarded as a plane, When the luminance of dots obtained from the luminance linear interpolating means is selected and it is considered that the figure is not regarded as a plane but further specular reflection occurs, the specular reflection component of the luminance of dots obtained by the normal interpolation means is subjected to the luminance linear interpolation. And a selecting unit for selecting by adding to the brightness of the dot obtained from the means, and storing the brightness of each dot selected by the selecting unit in the memory.

Furthermore, in the present invention, the relationship between the angles of the specular reflection components is examined, and thereby it is determined whether the specular reflection components can be ignored, and based on the result, it is determined whether or not the calculation of the specular reflection components is omitted. A graphic shading method is provided. Furthermore, the present invention provides a figure shading method in which it is determined whether or not the display surface can be regarded as a flat surface, and when it is determined that the display surface can be regarded as a flat surface, the polyhedron display method is switched to perform luminance calculation.

[Action]

The brightness of each point on the curved surface to be displayed is composed of three components, an ambient light reflection component, a diffuse reflection component, and a specular reflection component, as described later. Conventionally, the luminance interpolation method (linear interpolation method) and the normal interpolation method have been considered as completely different contents. However, the inventors of the present invention have found that the calculation method of the ambient light reflection component and the diffuse reflection component of both is the same value. When this property is used, it is easier to calculate the ambient light reflection component and the diffuse reflection component by the luminance interpolation method, so that the luminance interpolation method can perform the calculation faster than the normal interpolation method. Therefore, when displaying by the normal interpolation method, the specular reflection component is calculated by the normal interpolation method, and the ambient light reflection component and the diffuse reflection component are calculated by the luminance interpolation method, which enables high-speed processing.

Next, the specular reflection component has extremely strong directivity, and has a property that it occurs only at a specific angle and hardly occurs when deviating from that angle. However, conventionally, the value was calculated even when the specular reflection was extremely weak and could be practically ignored. This calculation requires vector inner product calculation and nth power (n = 50 to 200) of the result, as will be described later, and thus the calculation amount is very large. Therefore, it means that the calculation was extremely useless. Therefore, regarding the specular reflection component, the angle relationship is first examined to determine whether or not specular reflection can be ignored. If specular reflection can be ignored, the calculation time can be shortened considerably by omitting the calculation.

Furthermore, the calculation can be simplified even when the sample points can be regarded as existing on a plane. In the case where the display target surface is a flat surface and the flat surface is cut off by a curved surface, many sample points are taken on the flat surface and divided into minute flat surfaces in order to find the line of intersection between the flat surface and the curved surface. In this case, since the sample points are on the plane, the brightness calculation results obtained by the polyhedron display method, the brightness interpolation method, and the normal interpolation method are all the same. Therefore, even in the case of the luminance interpolation method and the normal interpolation method, the normal vector at the sample point is examined, it can be considered that it exists on the plane, and it is determined whether the polyhedral display method can be substituted. If the substitution is possible, the polyhedral display method is used. The calculation can speed up the process. If the light source and the viewpoint are at infinity, the microscopic surfaces on the same plane all have the same brightness, so it is judged whether they are on the same plane or not. In that case, the calculation can be omitted by setting the already obtained luminance as the luminance of the plane, and the processing can be speeded up.

〔Example〕

Before describing the embodiments of the present invention in detail, first, it is shown that the calculation of the ambient light reflection component and the diffuse reflection component is the same in the calculation of the luminance by the luminance interpolation method and the normal interpolation method. The structural example of the figure shading apparatus using is shown.

It is well known to express the brightness of an object surface as a relationship among the direction of the object surface (normal vector), the reflection coefficient of the surface, the light source position, the light source intensity, and the viewpoint position.
n), “Models of Light Reflection
Models of Light Reflection for Computer Synthesi
zed Pictures) ”according to SIGGRAPH '77 Proceeding.

Now, the principle of shading based on the reflection model of FIG. 2 will be described. In FIG. 2: is a unit normal vector indicating the direction of the reflecting surface at the reflection point P: is a unit vector indicating the direction of the light source viewed from the reflection point P: is a unit vector indicating the direction of the viewpoint viewed from the reflection point P: L Each vector is defined with a unit vector indicating an intermediate direction between the directions indicated by and V. At this time, the light intensity (luminance) I at the reflection point P viewed from the viewpoint is I = KaIa + Is {Kd (•) + Ks (•) ⁿ } (1) for each of the red, green, and blue components. Where KaIa is the ambient light reflection component, KdIs (・)
Is a diffuse reflection component, KsIs (·) ⁿ is a specular reflection component, and the brightness I is given by the sum of these three components. Where Ia: Incident intensity of ambient light on the display surface Is: Intensity of light incident on the display surface from the light source Ka: Ambient light reflection coefficient Kd: Diffuse reflection coefficient Ks: Specular reflection coefficient n: Specular directivity index Is. Note that (·) represents the inner product of the vectors. The principle relationship between the brightness calculation method of Expression (1) and three kinds of brightness calculation methods such as the normal interpolation method is as follows. In the polyhedron display method and the luminance interpolation method, the equation (1) is calculated only at the sample points. In the normal interpolation method, the normal vector is obtained for all points, and the result is used to calculate equation (1) at all points. As a specific example, consider the case of displaying an ellipsoid as shown in FIG. At this time, it is assumed that sample points such as P ₁ , P ₂ , P ₃ , P ₄ ... Exist on the surface of the ellipsoid. Then, for example, the brightness Ip at the point P having the relationship as shown in FIG. 3 in the distance ratio with respect to the sample points P ₁ , P ₂ , P ₃ is calculated by the following three methods, respectively.

First, in the polyhedron display method, as shown in Fig. 4, P ₁ , P
_2, obtains the luminance I _1, I _2, I ₃ in the P _3, the brightness Ip at the point P, regardless of the position of the P Calculate with.

In the case of the luminance interpolation method, as shown in FIG.
The luminances Ia and Ib at points Pa and Pb on ₁ P ₂ and P ₁ P ₃ are obtained, and Ip is obtained from these Ia and Ib. At this time, Ia and Ib are P ₁ and P ₂ and P ₁
And the ratio of the distances to P ₃ are determined from I ₁ , I ₂ , and I ₃ . As a result, Ia = αI ₁ + (1-α) I ₂ (3) Ib = βI ₁ + (1-β) I ₃ (4). Similarly, Ip is determined by the ratio of the distances from Pa and Pb, and Ip = γIa + (1-γ) Ib (5). Therefore, substituting equations (3) and (4) into equation (5) and rearranging, Ip = {α · γ + β (1-γ)} I ₁ + (1-a) γI ₂ + (1-β) (1- γ) I ₃ (6). However, Is. Here, the following assumptions are made. The ambient light intensity Ia is evenly incident on all points on the display target surface. The light source is a parallel light beam or a point light source at infinity, and the light source direction vector L and the incident intensity Is from the light source are also the same at all points on the display target surface. It is assumed that the optical properties of the surface, that is, the reflection coefficients Ka, Kd, Ks and the directivity index n are the same at all points on one display target surface. The viewpoint is infinite,
The viewpoint direction vector V is also the same at all points on the surface. Therefore, the intermediate vector H is also the same at all points on the surface. At this time, I ₁ , I ₂ , and I ₃ are expressed as follows.

I ₁ = KaIa + Is {Kd (・₁ ) + Ks (・₁ ) ⁿ } I ₂ = KaIa + Is {Kd (・₂ ) + Ks (・₂ ) ⁿ }
_{(7) I 3 = KaIa +} Is {Kd (· 3) + Ks (· 3) n} When this equation (7) to organize into equation (6) Ip = KaIa + IsKd [{α · γ + β (1 -γ)} (・
₁ ) + (1-α) γ (· ₂ ) + (1-β) (1-γ) (· ₃ )] + IsKs [{α · γ + β (1-γ)} (· ₁ ) ⁿ + (1- α) γ (· ₂ ) ⁿ + (1-β) (1-γ) (· ₃ ) ⁿ ] (8).

In the case of the normal interpolation method, first, the normal vector p at the point P
Is calculated, and the brightness Ip at the point P is calculated based on that value. The normal vector p at the point P is obtained from the normal vectors ₁ , ₂ and _{3 at the} points P ₁ , P ₂ and P _{3 as} follows. First side point P ₁ on the P ₂ Pa and P ₁ P ₃ on the normal vector a at a point Pb of using the _{1, 2, 3} b, defined by the ratio of epilepsy distance as follows.

a = α ₁ + (1-α) ₂ (9) b = β ₁ + (1-β) ₃ (10) Next, the normal vector p is calculated by using the ratio of the distances between the point P and the points Pa and Pb. , Ia and Ib are defined as follows.

p = γIa + (1-γ) Ib (11) Then, by substituting the equations (9) and (10) into the equation (11), p = {α · γ + B (1-γ)} ₁ + (1-α ) Γ ₂ + (1-β) (1-γ) ₃ (12). Considering the same assumption as when deriving equation (8), the brightness Ip at the point P is Ip = KaIa + Is {Kd (· p) + Ks (· p) ⁿ }.
(13) Substituting equation (12) into this, Ip = KaIa + IsKd [{α ・ γ + β (1-γ)} (・₁ ) + (1-α) γ (・₂ ) + (1-β) (1-γ) (・₃ )] + IsKs (・ p) ⁿ (14) is obtained.

Here, equations (8) and (14) are compared. The term with coefficient Ka is the ambient light reflection component, the term with coefficient Kd is the diffuse reflection component, and the term with coefficient Ks is the specular reflection component. Comparing these components, it can be seen that the ambient light reflection component and the diffuse reflection component are exactly the same. That is, the ambient light reflection component and the diffuse reflection component obtained by the luminance interpolation method and the normal interpolation method have the same value. On the other hand, the specular reflection component is only one term of (.) ^{N in} the case of luminance interpolation, but it is an nth degree polynomial of (.) In the case of normal interpolation and generally has different values.

Next, consider the properties of the specular reflection component ((・
) The range of values is 0 ≦ (·) ≦ 1, and the directivity index n is generally a value of 50 to 200. (·) ⁿ has a value of almost 1 only in the vicinity of (·) = 1. , Otherwise, it has a value of almost 0. That is, specular reflection is very sensitive to angle, and strong reflection occurs only at a specific angle, and when it deviates from this angle, the reflection sharply decreases, and the value is almost 0 at most angles. Therefore, when the specular reflection is almost zero, the luminance obtained by the luminance interpolation and the luminance obtained by the normal interpolation are the same due to the properties of the ambient light reflection component and the diffuse reflection component described above. If the specular reflection can be ignored by utilizing this property, the brightness calculation by the normal interpolation method may be replaced by the brightness interpolation method. When calculating with the normal interpolation method, it is necessary to find the normal vector of each display point as described above, and to find the inner product with the light source direction vector,
It can be seen that the luminance interpolation obtained by simple linear interpolation can obtain the luminance of each point much faster than before by this method.

Next, consider the case where the sample points are on one plane. As described above, when the plane is cut out by a curved line, the plane is divided into minute polygons and an approximate calculation is performed in order to find the line of intersection. When this plane is displayed, the vertices of this polygon are often sample points as they are. In this case, many sample points exist on the plane,
In such a case, since the sample points and all points between them have the same brightness, exact calculation by brightness interpolation or normal interpolation is not necessary, and polyhedron display is sufficient.
Therefore, the amount of calculation can be reduced by first checking the normal vectors of the sample points and determining that the normal vectors are equal to each other and performing the polyhedral display when the normal vectors are judged to be equal.
Further, also at this time, it is possible to omit the calculation of the specular reflection component at the sample point when the specular reflection can be ignored by determining whether the specular reflection can be ignored.

FIG. 1 shows an embodiment of the figure shading apparatus of the present invention using these ideas. Figure shading device 20
0 generates shading data under the control of the host computer 100 and outputs the result to the frame memory 300. The shading data stored in the frame memory 100 is read by the color CRT 400 and displayed on the screen. The figure shading device 200 comprises a microcomputer 10, a normal interpolation luminance calculation circuit 50, a luminance interpolation circuit 21, selectors 53 and 28, registers 14, 16, and 18, a gate 51, and an adder 52. The microcomputer 10 comprises a central processing unit 11 and a memory 12. Although the central processing unit 11 is shown as having its function divided into blocks, an ordinary central processing unit is used. Here, the outline of the function of the graphic shading device is as follows. First, figure shading device 20
0 receives from the host computer 100 display mode data indicating which of normal interpolation mode, luminance interpolation mode, and polyhedron display mode is used for display, light source position, light source intensities Ia, Is, and viewpoint position display method data. Next, the optical characteristic data of the object surface is received for each object to be displayed. Then, the geometric data of the sample points is received, the brightness of the surface of the display target object is calculated, and the calculated brightness is output to the frame memory 300. The details of the operation will be described below.

First, display mode data indicating which of polyhedron display, luminance interpolation, and normal interpolation is used for luminance calculation is transferred from the host computer 100 to the figure shading device 200. Further, the ambient light source intensity Ia, the light source intensity Is for shading, the light source direction vector indicating the direction of the light source, and the viewpoint direction vector are transferred. The data relating to the display object is then transferred, first the reflection coefficients Ka, Kd, Ks and the directivity index n of the surface of the first object. Hereinafter, the reflection coefficient and index data are transferred each time the optical characteristics of the object surface change.
Next, the coordinate values P ₁ , P ₂ , P ₃ ... And the normal vector ₁ , ₂ , _3, ... Of the sample points on the surface of the style are transferred. The unit of transfer at this time is a unit in which P ₁ , P ₂ , P _3, ... Form one polygon. The figure shading device 200 performs the brightness calculation processing for one polygon, and when the processing is completed, receives the sample point data forming the next polygon and processes the polygon.

At this time, the data transferred from the host computer 100 is stored in the memory 12 of the microcomputer 10 and read by the central processing unit 11 as necessary to perform the necessary processing. First, the central processing unit 11 stores the mode data in the memory 12 when the mode data is transferred. Then, the process 13 of performing mode determination and outputting the result to the mode register 14
Do. Next, when the information on the light source and the viewpoint is received, the contents are stored in the memory 12. When the information of the optical characteristic data of the object surface is received, the value is stored in the memory 12. Next, when the sample point data forming one polygon is received, it is stored in the memory 12. And
Processing for determining flatness from the normal vector data ₁ , ₂ , ₃ , ... And outputting the result to the flatness register 16 15
Do. Further, the light source direction vector and the viewpoint direction vector are read out, compared with the normal vectors ₁ , ₂ , ₃ , ... To determine whether or not specular reflection can be ignored, and the result 17 is output to the specular reflection register 18. Reference numeral 50 is, for example, a normal interpolation luminance calculation circuit disclosed in Japanese Patent Laid-Open No. 61-70666, which is a circuit for calculating the specular reflection component by the normal interpolation method and outputting the value. In the normal interpolation mode, the central processing unit 11 transfers the data required by the normal interpolation brightness calculation circuit 50 from the memory 12 and the normal interpolation brightness calculation circuit 50.
The two processes 20 for starting the are executed. 21 is, for example, Japanese Patent Sho 57
This is the luminance interpolation circuit disclosed in Japanese Patent Publication No. 57715. In the luminance interpolation mode, the central processing unit 11 reads data from the memory 12, performs a calculation process 22 of the luminances I ₁ , I ₂ , I ₃ ... At the sample points, and further transfers the result to the luminance interpolation circuit 21. Do 23. In the polyhedron display mode, the calculation of the average value of the luminance and the processing 24 of its output are performed. Processing
The procedure for calculating the luminance of each sample point in 22 is as shown in FIG. First, the brightness of the ambient light reflection component and the diffuse reflection component is calculated, and then the presence or absence of specular reflection is determined,
If there is, the component is calculated and added.

Returning to FIG. 1, the brightness interpolation circuit 21 performs brightness calculation by brightness interpolation and outputs the brightness of the display point and the address signal on the screen. The central processing unit 11 performs brightness calculation by brightness interpolation in process 24 and outputs the brightness of the display point and the address signal on the screen. The process 24 outputs the luminance of the display point obtained by averaging and the address signal on the screen.

In this device, in the normal interpolation mode, the specular reflection component is obtained by the normal interpolation luminance calculation circuit 50, the ambient light reflection component and the diffuse reflection component are obtained by the luminance interpolation circuit 21, and the sum is calculated by the adder 52 and output. To do. When the specular reflection can be ignored, the output of the specular reflection register 18 blocks the output of the normal interpolation luminance calculation circuit 50 by the gate 51 so that only the output of the luminance interpolation circuit 21 can be obtained from the adder 52. When it is determined that the plane can be regarded as a plane, the selector 53 selects the output of the processing 24 from the outputs of the processing 24 and the adder 52 according to the contents of the planarity register 16.

The selector 28 is a selector depending on the contents of the mode register 14.
One of the output of 53, the output from the luminance interpolation circuit 21, and the result of processing 24 is selected and output to the frame memory 300. Normal interpolation luminance calculation circuit 50, luminance interpolation circuit 21, and processing
The address signal on the screen output by 24 is the frame memory 30.
It also serves as an address signal of 0, and the normal line interpolation luminance calculation circuit 50, the luminance interpolation circuit 21, and the luminance data output by the processing 24 are stored at the address of the frame memory 300. As a result, all the results of the brightness calculation are stored in the frame memory 300. By reading out this content and displaying it on the CRT 400, the display of the shaded curved surface appears on the tube surface of the CRT.

The procedure of process 22 in this embodiment is shown in FIG. In this case, when the luminance interpolation circuit 21 is used in the normal interpolation mode, control is performed so that the specular reflection component is not input to the circuit 21. When it is determined that the plane can be regarded as a plane, the normal interpolation luminance calculation circuit 50 and the luminance interpolation circuit 21 are not used to display a polyhedron, so that the processing of 22 includes a specular reflection component. Therefore, the processing of 80 to 83 is performed.

In the embodiment of the present invention, when a large number of minute surfaces on the same plane appear, an area for storing the calculation result in the process 24 of FIG. 1 is provided in the memory 12, and as shown in FIG. If it is determined that the plane is the same plane as the previous plane, as in 92, the brightness of the plane is calculated in 93 if different, and the result is stored in 94. If it is on the same plane, the previous brightness is read out as 95, and this is the current brightness.

〔The invention's effect〕

According to the present invention, when displaying a figure of a three-dimensional object, among the brightness Ip of each dot P, the brightness of the ambient light reflection component and the brightness of the diffuse reflection component are linearly calculated based on the coordinates Pi of the sample points. The brightness of the specular reflection component of the brightness Ip of the reflection point P is calculated by the normal interpolation method by the normal interpolation means based on the unit normal vector Ni of the sample point. In addition, since the average value of the brightness calculated at the sample points is taken on the surface determined to be a plane, the speed of the shading calculation of the brightness in the figure of the three-dimensional object can be increased, and the device configuration is simple. There is an effect that can be realized by.

[Brief description of drawings]

FIG. 1 is a diagram showing a device configuration of an embodiment of the present invention, FIG. 2 is a diagram showing a definition of a vector used for brightness calculation, and FIG. 3 is a diagram showing a positional relationship between sample points and display points on an ellipsoid. Figure,
FIG. 4 is a diagram for explaining the brightness calculation method in the brightness interpolation method,
FIG. 5 is a diagram for explaining the normal interpolation method, FIG. 6 is a diagram showing a luminance calculation procedure in the central processing unit in the embodiment of the present invention, and FIG. 7 shows many minute planes on the same plane. It is a figure which shows the brightness calculation procedure in the case. 100 ... Host computer, 200 ... Graphic shading device, 300 ... Frame memory, 400 ... CRT, 10 ... Microcomputer, 11 ... Central processing unit, 12 ... Memory, 21 ... Luminance interpolation circuit, 14 ... Mode register, 16 ... Planarity register, 18 ... Specular reflection register, 50 ... Specular reflection component calculation circuit by normal interpolation method, 52 ... Adder.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shigeo Tsujioka Inventor Shigeo Tsujioka, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa, Ltd. Microelectronics Equipment Development Laboratory, Hitachi, Ltd. 5-2-1, Hitachi Ltd. Omika factory (56) References JP-A-62-186373 (JP, A)

Claims (1)

[Claims] 1. When displaying a three-dimensional figure on a display means,
In a figure shading device for calculating the brightness of each dot on a display figure and performing shading and storing it in a memory, each of the ambient light reflection component and the diffuse reflection component of the dot brightness is the ambient light reflection component of the sample point brightness. And a linear interpolation method for calculating a specular reflection component of the brightness of the dot by a normal interpolation method based on a normal vector of sample points Means, a brightness average value calculating means for calculating the average value of the brightness of the sample points, and calculating the brightness of the dots by the method of assigning it to the dots, and whether the figure to which the dots belong can be regarded as a plane. Flatness determining means for determining, and if the flatness determining means determines that the figure can be regarded as a plane, the brightness average value calculating means When the brightness of the dots to be output is selected and the flatness judging means judges that the figure cannot be regarded as a plane, the brightness of the dot obtained from the brightness linear interpolating means is selected and the figure is not regarded as a plane. Further, when specular reflection is considered to occur, the specular reflection component of the luminance of the dot obtained from the normal interpolation means is added to the luminance of the dot obtained from the luminance linear interpolation means to select it. A figure shading device characterized in that the brightness of each dot selected by the means is stored in the memory.