JP2010224733A - Rendering device and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the color of an edge portion of an image after rendering from becoming unnatural when a source image includes the edge whose α-value changes a great deal in carrying out rendering by jointly using bilinear filter processing and α-blending. <P>SOLUTION: A bilinear filter 1 multiplies each source color value of four source pixels surrounding an interpolation point in a source image, by each α-value and applying bilinear filter processing to four source color values after α-value multiplication to compute an interpolation point source color value, and applies bilinear filter processing to four α-values to compute an interpolation point source α-value. An α-blending part 2 mixes a destination color value of a destination pixel and the interpolation point source color value based on the interpolation point source α-value to compute a color value D' of the destination pixel after α-blending. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a drawing processing technique, and more particularly, to a rendering apparatus and a program including a bilinear filter and an α blending unit.

Techniques related to rendering of sprite images and the like include α blending and bilinear filter processing. Here, α blending is a color value (luminance of each component of R, G, B) of each pixel of an image to be rendered (hereinafter referred to as a source image) and an α value indicating transparency of each pixel, Each pixel (source image and destination image) of the destination image after the source image is rendered based on the color value of each pixel of the rendering destination image (hereinafter referred to as the destination image) that becomes the background of the source image. Is a technique for calculating the color value of each pixel in the overlapping area. More specifically, in this α blending, as shown in FIG. 3, the color value of one pixel constituting the source image (hereinafter referred to as source pixel) is SC, and the pixel of the destination image corresponding to this source pixel. When the color value (hereinafter referred to as the destination pixel) is D, the color value D ′ shown in the following equation is calculated and used as the color value of the destination pixel after rendering.
D ′ = α * SC + (1−α) * D (1)
Thereby, in the rendered image, it is possible to produce a state where the destination image before rendering can be seen through with transparency corresponding to the α value over the source image.

On the other hand, in bilinear filter processing, when rendering a source image such as a sprite image to a destination image by enlarging or rotating the source image, the source image that is the rendering target (when enlarging or rendering is enlarged, etc.) And a linear interpolation processing means for calculating a color value of an interpolation point that occupies the same position as the destination pixel of the destination image of the rendering destination. More specifically, in the bilinear filter processing, as shown in FIG. 4, four surrounding pixels P surrounding the interpolation point PP (x, y) corresponding to the position of the destination pixel among the pixels constituting the source image. Using the color values SC0, SC1, SC2, and SC3 of (m, n), P (m + 1, n), P (m, n + 1), and P (m + 1, n + 1), the calculation shown in the following equation is performed for interpolation. A color value SC (x, y) corresponding to the point PP (x, y) is calculated.
SC (x, y)
= B0 * SC0 + B1 * SC1 + B2 * SC2 + B3 * SC3 (2)

Here, B0 to B3 correspond to the four pixels P (m, n), P (m + 1, n), P (m, n + 1), and P (m + 1, n + 1) around the interpolation point PP (x, y). This is a bilinear coefficient determined by the positional relationship. When the interpolated point coordinate values x and y are fractional parts p and q when the pixel position interval of the four surrounding pixels is 1, the bilinear coefficients B0 to B3 are given by the following equations.
B0 = (1-p) * (1-q) (3)
B1 = (1-q) * p (4)
B2 = (1-p) * q (5)
B3 = p * q (6)

The bilinear coefficients B0 to B3 have the relationship shown in the following equation.
B0 + B1 + B2 + B3
= (1-p) (1-q) + p (1-q) + (1-p) q + pq
= 1 (7)

In rendering, the above-described bilinear filter processing and α blending may be used in combination. FIG. 5 shows the contents of rendering processing using this bilinear filter processing and α blending together. As shown in FIG. 5, in rendering that uses bilinear filtering and α blending in combination, first, four pixels P (m, n), P (m + 1, P) around the interpolation point PP (x, y) in the source image. n), P (m, n + 1), and P (m + 1, n + 1) using the α values A0, A1, A2, and A3, the bilinear filter processing shown in the following equation is executed, and the interpolation point PP (x, y) Α value A to be applied to is calculated.
A = B0 * A0 + B1 * A1 + B2 * A2 + B3 * A3 (8)

Further, the color values SC0 and SC1 of the four pixels P (m, n), P (m + 1, n), P (m, n + 1), and P (m + 1, n + 1) around the interpolation point PP (x, y). , SC2 and SC3, the bilinear filter processing shown in the following equation is executed to calculate the source color value SC of the interpolation point PP (x, y).
SC = B0 * SC0 + B1 * SC1 + B2 * SC2 + B3 * SC3 (9)

Then, using the source color value SC and α value A of the interpolation point PP (x, y) obtained by the above two types of bilinear filter processing and the destination color value D of the destination pixel, the following expression is given. α blending is executed, and the color value D ′ of the destination pixel after rendering is calculated.
D ′ = A * SC + (1-A) * D (10)
Patent Document 1 is an example of a document relating to rendering using bilinear filter processing and α blending in combination.

JP 2006-18382 A

  By the way, in the rendering using the conventional bilinear filter and α blending described above, when the source image includes an edge whose α value greatly changes, the rendering of the pixel to which a small α value should be originally applied in the rendered image. There is a problem in that the color appears excessively on the edge portion of the rendered image, and the edge portion becomes an unnatural color. Hereinafter, this problem will be described in detail with reference to FIG.

In the example illustrated in FIG. 6, the sprite 100 that is the source image is rendered on the background image 200 that is the destination image. Here, the sprite 100 has been subjected to enlargement processing, and has a circular region 101 having an α value of 1 and a region 102 around which the α value is 0. In the illustrated example, the sprite 100 is rendered on the background image 200 by using bilinear filtering and α blending together. In FIG. 6, the interpolation point PP (x, y) in the sprite 100 is on the edge of the circular region 101, and among the four pixels around the interpolation point PP (x, y), the source pixel P (m, n) and P (m, n + 1) are in the circular region 101 having an α value of 1, and the source pixels P (m + 1, n) and P (m + 1, n + 1) are in a region 102 having an α value of 0. is there. Here, since the α value of the source pixels P (m + 1, n) and P (m + 1, n + 1) is 0, the color of the pixel of the background image 200 should be transmitted after rendering. Therefore, after rendering, the color of the pixel at the interpolation point PP (x, y) on the edge of the circular region 101 is a mixture of the color of the pixel in the circular region 101 and the color of the pixel in the background region 200. Should not be a mixture of the colors of the pixels in the region 102 where the α value is zero.

  However, in rendering using both conventional bilinear filtering and α blending, the color values of the source pixels P (m, n), P (m + 1, n), P (m, n + 1), and P (m + 1, n + 1) are described above. Bilinear filter processing of Expression (9) is performed to calculate a color value SC to be passed to α blending as post-processing. Therefore, the color value to be subjected to α blending includes the color values SC1 and SC3 of the pixels in the region where the α value is 0, as shown in the above equation (9), and interpolation after α blending is performed. The color value of the pixel at the point PP (x, y) also includes color values SC1 and SC3 that should not be included originally. For this reason, the edge of the circular area 101 of the sprite 100 after rendering becomes an unnatural color. As described above, the typical example in which the α value on one side of the edge is 1 and the α value on the other side is 0 in the source image has been described. Similarly, when the α value changes greatly from the edge to the boundary, there is a problem that the color of the edge after rendering becomes unnatural.

  The present invention has been made in view of the circumstances described above, and when rendering is performed by using bilinear filter processing and α blending together, the source image to be rendered includes an edge whose α value greatly changes. It is an object of the present invention to provide a technical means for preventing the color of the edge portion of an image after rendering from becoming unnatural.

  The inventor of the present application diligently studied the above problem, and as a result, came up with the following idea. That is, in order to prevent the above-described problem from occurring, as shown in FIG. 1, four source pixels P (m, n) and P (m + 1) around the interpolation point PP (x, y) in the source image. , N), P (m, n + 1), each source color value SC0, SC1, SC2, SC3 of P (m + 1, n + 1) and a destination color value D of the destination pixel are α-blended, It is thought that the color value D ′ of the destination pixel after rendering should be calculated by performing binary filter processing on the four color values obtained as a result of these four types of α blending.

When such rendering is performed, the color value D ′ of the destination pixel after rendering is represented by the following equation.
D ′ = B0 * (A0 * SC0 + (1-A0) * D) +
B1 * (A1 * SC1 + (1-A1) * D) +
B2 * (A2 * SC2 + (1-A2) * D) +
B3 * (A3 * SC3 + (1-A3) * D) (11)

  In the right side of the above equation, each value in the four parentheses multiplied by the bilinear coefficients B0 to B3 is the source color value SC0, SC1, SC2, SC3 and the destination color value D of the destination pixel. It is the result of α blending.

In the case of the example shown in FIG. 6, since the α values A0 and A2 in the above equation (11) are 1 and the α values A1 and A3 are 0, the color value D ′ of the destination pixel after rendering is expressed by the following equation: It becomes like this.
D ′ = B0 * (1 * SC0 + (1-1) * D) +
B1 * (0 * SC1 + (1-0) * D) +
B2 * (1 * SC2 + (1-1) * D) +
B3 * (0 * SC3 + (1-0) * D)
= B0 * SC0 + B1 * D + B2 * SC2 + B3 * D (12)
As described above, when the rendering shown in FIG. 1 is performed, the color values D ′ of the destination pixels after rendering are the color values SC0 and SC2 of the pixels in the circular area 101 of the sprite 100 and the color of the pixels of the background image. The value D is mixed and becomes the color value of the originally intended edge.

  As described above, in rendering that uses bilinear filter processing and α blending in combination, if the bilinear filter processing is performed after α blending, the above-described problem that the edge color becomes unnatural can be prevented. Can do. However, the existing rendering device is configured on the assumption that α blending is executed after bilinear filter processing. As described above, bilinear filter processing is post-processing of α blending processing. This has a large effect on the configuration of the system and is difficult to implement in practice.

  Therefore, in the present invention, the basic calculation order of performing the α blending after the bilinear filter processing is not broken, and the bilinear filter is selected by selecting a portion that can be calculated using the bilinear filter from all the α blending operations. And the result is transferred to α blending, and as a result, the same operation as the above equation (11) is performed. Specifically, it is as follows.

First, the above equation (11) can be modified as follows.
The error value D ′ is represented by the following equation.
D ′ = B0 * (A0 * SC0 + (1-A0) * D) +
B1 * (A1 * SC1 + (1-A1) * D) +
B2 * (A2 * SC2 + (1-A2) * D) +
B3 * (A3 * SC3 + (1-A3) * D)
= B0 * A0 * SC0 + B0 * (1-A0) * D +
B1 * A1 * SC1 + B1 * (1-A1) * D +
B2 * A2 * SC2 + B2 * (1-A2) * D +
B3 * A3 * SC3 + B3 * (1-A3) * D
= B0 * A0 * SC0 + B1 * A1 * SC1 +
B2 * A2 * SC2 + B3 * A3 * SC3 +
B0 * D-B0 * A0 * D + B1 * D-B1 * A1 * D +
B2 * D-B2 * A2 * D + B3 * D-B3 * A3 * D
= B0 * A0 * SC0 + B1 * A1 * SC1 +
B2 * A2 * SC2 + B3 * A3 * SC3 +
(B0-B0 * A0 + B1-B1 * A1 +
B2-B2 * A2 + B3-B3 * A3) * D (13)

In the above equation (13), since the sum of the bilinear coefficients B0, B1, B2, and B3 is 1, the above equation (13) is as follows.
D ′ = B0 * A0 * SC0 + B1 * A1 * SC1 +
B2 * A2 * SC2 + B3 * A3 * SC3 +
{1- (B0 * A0 + B1 * A1 + B2 * A2 + B3 * A3)} * D
(14)

  In the present invention, the bilinear filter executes B0 * A0 * SC0 + B1 * A1 * SC1 + B2 * A2 * SC2 + B3 * A3 * SC3 and B0 * A0 + B1 * A1 + B2 * A2 + B3 * A3 on the right side of the above equation (14). Then, the α blending unit executes the calculation of the entire right side using these calculation results.

Here, B0 * A0 * SC0 + B1 * A1 * SC1 + B2 * A2 * SC2 + B3 * A3 * SC3 is the source of each of the four source pixels surrounding the interpolation point that is the destination pixel of the destination image that is the rendering destination in the source image The color values SC0, SC1, SC2, and SC3 are respectively multiplied by the α values A0, A1, A2, and A3 of the four source pixels, and the four source color values A0 * SC0 and A1 * SC1 after the multiplication of the respective α values. , A2 * SC2,
Interpolation point source color value obtained by performing bilinear filter processing using four bilinear filter coefficients B0, B1, B2, and B3 determined by the positional relationship between the four source pixels and the interpolation points for A3 * SC3 It is. B0 * A0 + B1 * A1 + B2 * A2 + B3 * A3 is a bilinear filter process using four bilinear filter coefficients B0, B1, B2, B3 for each α value A0, A1, A2, A3 of the four source pixels. This is the interpolation point source α value obtained by applying.

  In the α blending unit, the destination color value D of the destination pixel and the interpolation point source color value B0 * A0 * SC0 + B1 * A1 * SC1 + B2 * A2 * SC2 + B3 * A3 * SC3 are combined with the interpolation point source α value B0 * A0 + B1 *. Based on A1 + B2 * A2 + B3 * A3, mixing is performed, and the color value D ′ of the destination pixel after α blending shown in the above equation (14) is calculated.

  As described above, according to the present invention, the calculation of the above formula (11) can be performed as a result without destroying the basic calculation order of performing the α blending after the bilinear filter processing. Accordingly, when the source image to be rendered has an edge whose α value greatly changes, it is possible to prevent the color of the portion corresponding to the edge in the rendered image from becoming unnatural.

It is a figure which shows the processing content of the rendering which used together the bilinear filter process and alpha blending which this invention is going to implement | achieve. It is a block diagram which shows the structure of the rendering apparatus which is one Embodiment of this invention. It is a figure explaining alpha blending theory. It is a figure explaining a bilinear filter process. It is a figure which shows the processing content of the rendering which used the conventional bilinear filter process and (alpha) blending process together. It is a figure explaining the problem which arises in the conventional rendering.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 2 is a block diagram showing a configuration of a rendering apparatus according to an embodiment of the present invention. This rendering apparatus forms part of a circuit of an image processing LSI used in, for example, a game machine, and the process of rendering a sprite image into an image that is a display target of the game machine, for example, in the image processing LSI. Is to do. As illustrated, the rendering apparatus includes a bilinear filter 1, an α blending unit 2, a source image memory 3, and a destination image memory 4. Here, the source image memory 3 is a memory for storing image data of a source image to be rendered. The image data of the source image is a collection of pixel data indicating each pixel constituting the source image. Pixel data indicating one pixel is composed of data indicating the luminance of each of R, G, and B components of the color of the pixel and an α value indicating the transparency of the pixel. The destination image memory 4 is a memory that stores image data of a destination image that is a rendering destination of the source image.

When rendering is performed using bilinear filter processing and α blending together, the bilinear filter 1 includes the fractional parts p and q of the x and y coordinate values of the interpolation point PP (x, y) corresponding to the destination pixel, and rendering. Four source pixels P (m, n), P (m + 1, n), P (m, n + 1), P surrounding the interpolation point PP (x, y) corresponding to the destination pixel of the destination image. Each source color value SC0, SC1, SC2, SC3 of (m + 1, n + 1) and each source α value A0, A1, A2, A3 are given. In this case, the bilinear filter 1 first performs the calculation shown in the following equation.
AB0 = B0 * A0 (15)
AB1 = B1 * A1 (16)
AB2 = B2 * A2 (17)
AB3 = B3 * A3 (18)

Next, the bilinear filter 1 calculates the interpolation point source color value SC according to the following equation (19), and calculates the interpolation point source α value A according to the following equation (20).
SC = AB0 * SC0 + AB1 * SC1 + AB2 * SC2 + AB3 * SC3
...... (19)
A = B0 * A0 + B1 * A1 + B2 * A2 + B3 * A3 (20)

The bilinear filter 1 sends the interpolation point source color value SC and the interpolation point source α value A to the α blending unit 2. The α blending unit 2 reads the destination color value D of the destination pixel from the destination image memory 4, and uses the destination color value D, the interpolation point source color value SC, and the interpolation point source α value A to The calculation shown in the equation is performed to calculate the destination color value D ′ after rendering.
D ′ = SC + (1-A) * D (21)

In normal α blending, the interpolation point source color value SC is multiplied by the α value, but in this embodiment, the interpolation point source color value SC is not multiplied by the α value as shown in the above equation (21). This is because in the present embodiment, the bilinear filter 1 outputs, as the interpolation point source color value SC, the result of performing bilinear filter processing on the four source color values multiplied by the α value. In the present embodiment, the calculation result of the above equation (21) is the same as the above equation (14) as shown in the following equation (22). Therefore, even when the source image to be rendered includes an edge whose α value greatly changes, it is possible to prevent the color of the edge portion of the rendered image from becoming unnatural.
D '= SC + (1-A) * D
= (AB0 * SC0 + AB1 * SC1 + AB2 * SC2 + AB3 * SC3) +
{1- (B0 * A0 + B1 * A1 + B2 * A2 + B3 * A3)} * D
= B0 * A0 * SC0 + B1 * A1 * SC1 +
B2 * A2 * SC2 + B3 * A3 * SC3 +
{1- (B0 * A0 + B1 * A1 + B2 * A2 + B3 * A3)} * D
...... (22)
The α blending unit 2 overwrites the destination image memory 4 with the color value D ′ as the color value of the destination pixel after rendering.

  As described above, according to the present embodiment, rendering that uses bilinear filter processing and α blending is performed without destroying the order of operations of performing α blending after bilinear filter processing. Even when the source image to be rendered includes an edge that varies greatly, it is possible to prevent the color of the edge portion of the rendered image from becoming unnatural.

  Although one embodiment of the present invention has been described above, the present invention may have other embodiments. For example:

(1) As shown in the following equation, the bilinear filter 1 may output the interpolation point source color value SC obtained by dividing the interpolation point source color value SC of the above equation (19) as the interpolation point source color value SC. Good.
SC = (AB0 * SC0 + AB1 * SC1 + AB2 * SC2 + AB3 * SC3) / A
...... (23)

In this aspect, the subsequent α blending unit 2 can obtain the rendered destination color value D ′ having the same value as the above equation (14) by performing normal α blending as shown in the following equation.
D '= A * SC + (1-A) * D
= A * {(AB0 * SC0 + AB1 * SC1 +
AB2 * SC2 + AB3 * SC3) / A} + (1-A) * D
= (AB0 * SC0 + AB1 * SC1 + AB2 * SC2 + AB3 * SC3) +
(1-A) * D
= (AB0 * SC0 + AB1 * SC1 + AB2 * SC2 + AB3 * SC3) +
{1- (B0 * A0 + B1 * A1 + B2 * A2 + B3 * A3)} * D
= B0 * A0 * SC0 + B1 * A1 * SC1 +
B2 * A2 * SC2 + B3 * A3 * SC3 +
{1- (B0 * A0 + B1 * A1 + B2 * A2 + B3 * A3)} * D
(24)

  Therefore, also in this aspect, the same effect as the above embodiment can be obtained. Further, this aspect has an advantage that the calculation content of the α blending unit 2 does not have to be changed from normal α blending. In this aspect, the interpolation point source color value SC output from the bilinear filter 1 is not multiplied by the α value (specifically, the interpolation point source α value A). There is an advantage that it is not necessary to change the calculation content of the luminance operation even when other calculation means for performing the luminance operation is interposed between the unit 2 and the unit 2.

(2) In the above embodiment, the pixel data of each source pixel constituting the source image includes the α value. However, the mode of associating the α value with the source pixel is not limited to this. For example, the α value may be associated with the color value such that α = 1 for a pixel having a certain color value and α = 0 for another pixel having a certain color value.

(3) The present invention is a dedicated hardware provided with the bilinear filter 1 and the α blending unit 2 of the above-described embodiments (including the modified aspects as shown in the above (1) and (2)). In addition to the implementation, the computer may be implemented as a computer program that causes the bilinear filter 1 and the α blending unit 2 of the above embodiments to function.

DESCRIPTION OF SYMBOLS 1 ... Bilinear filter, 2 ... (alpha) blending part, 3 ... Source image memory, 4 ... Destination image memory.

Claims (4)

In the source image, each source color value of the four source pixels surrounding the interpolation point that becomes the destination pixel of the destination image that is the rendering destination in the source image is multiplied by each α value of the four source pixels, and each α value multiplication is performed. Bilinear filter processing using four bilinear filter coefficients determined by the positional relationship between the four source pixels and the interpolation point is performed on the subsequent four source color values, and an interpolation point source is obtained based on the result. A bilinear filter that calculates a color value and performs bilinear filter processing using the four bilinear filter coefficients on each α value of the four source pixels to calculate an interpolation point source α value;
An α blending unit that mixes the destination color value of the destination pixel and the interpolation point source color value based on the interpolation point source α value, and calculates the color value of the destination pixel after α blending. A rendering device characterized by: The bilinear filter outputs, as the interpolation point source color value, a result obtained by performing bilinear filter processing using the four bilinear filter coefficients on the four source color values after each α value multiplication,
The α blending unit multiplies the destination color value by a value obtained by subtracting the interpolation point source α value from 1, and adds the multiplication result and the interpolation point source color value to obtain the α blended value. The rendering apparatus according to claim 1, wherein the color value of the destination pixel is calculated. The bilinear filter performs bilinear filter processing using the four bilinear filter coefficients on the four source color values after each α value multiplication, and divides the result by the interpolation point source α value. Is output as the interpolation point source color value,
The α blending unit multiplies the destination color value by a value obtained by subtracting the interpolation point source α value from 1 and multiplies the multiplication result by the interpolation point source α value and the interpolation point source color value. The rendering apparatus according to claim 2, wherein the color value of the destination pixel after α blending is calculated by adding. Computer
In the source image, each source color value of the four source pixels surrounding the interpolation point that becomes the destination pixel of the destination image that is the rendering destination in the source image is multiplied by each α value of the four source pixels, and each α value multiplication is performed. Interpolation point source color values are calculated by performing bilinear filter processing using the four bilinear filter coefficients determined by the positional relationship between the four source pixels and the interpolation points for the subsequent four source color values. And a bilinear filter that calculates an interpolation point source α value by subjecting each α value of the four source pixels to bilinear filter processing using the four bilinear filter coefficients;
A function as an α blending unit that mixes the destination color value of the destination pixel and the interpolation point source color value based on the interpolation point source α value and calculates the color value of the destination pixel after α blending. A computer program characterized by causing

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