JPH09282474A - Gradational image generating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a gradational image fast with a small work memory by an image generating method which generates an outline from vector data and paints its inside out to generate an image of characters, a figure, etc. SOLUTION: The outline generated from the vector data is divided into a group of fine straight lines which are within the range of at least one pixel, and the area value of the shadow of each fine straight line viewed from a predetermined direction is calculated and added or subtracted, pixel by pixel, to eliminate the need to generate a binary image, thereby shortening the processing time and reducing the work memory. Here, the area value of the shadow that the fine straight line generates when viewed from the predetermined direction is calculated and then an accurate gradation value can be calculated as compared with conversion from the binary image; when a memory for storing the gradational image is used as an area storage memory, almost no work memory is needed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image generating method, and more particularly to a gradation image generating method for displaying gradation data on a display device such as a display or a printer.

[0002]

2. Description of the Related Art Conventionally, in a display device such as a display or a printer, characters, figures, etc. are expressed in pixel units, stored as they are in a video memory called a bit map memory, and sequentially read out to obtain a free pattern. The method of displaying is adopted. Such an image generation method requires a large amount of memory as a bitmap memory because the display image is stored in pixel units, but since the correspondence between the display image and the memory is direct, the operability is high,
Further, since multi-color display is easy, this kind of image generation method is required.

As an image generation method of this type, outlines (also referred to as "contour lines") of characters and figures are stored as discrete data (also referred to as "vector data"), and this is stored. After reading the vector data and performing transformation processing such as enlargement, reduction, rotation, etc. as necessary,
Calculate the outline by interpolating with straight lines and curves,
A method of creating a binary image on a memory by filling the inside of this outline is known. But,
In this method, since the image is a binary image, there is a problem that rattling or a small size image is crushed due to the limit of resolution at a shaded portion or a curved portion. In order to solve this problem, there is known a method of first generating a binary image from vector data and then converting the generated binary image into a gradation image.

As such a gradation image generating method, for example, JP-A-2-275494 and JP-A-3-156 are available.
The method described in Japanese Patent No. 494 can be mentioned.
In these methods, in order to generate a gradation image, binary image data having a larger size than that is generated from vector data. For example, 5 as shown in FIG.
When it is attempted to generate a 5-gradation image having a size of × 6, first, a larger image of 10 × as shown in FIG.
A binary image of 12 sizes is generated from vector data. Next, the generated binary image is divided into small blocks of size 2 × 2, the number of on pixels included in each block is counted, and the number is used as a gradation value to generate a gradation image. ing.

[0005]

However, according to the above-mentioned conventional gradation image generation method, 2
Since it is necessary to generate a binary image and an extra memory for binary image recording is required, there is a problem that a large binary image recording memory is required in accordance with a large number of output gradations. is there.

Further, the above-described conventional gradation image generation method requires a two-step process of generating a binary image and converting it into a gradation image, which causes a problem that it takes time to generate an image.

Further, in the above-described conventional gradation image generating method, since a gradation image is generated from binary image data, especially when an image of a small size with a small number of output gradations is generated, There is a problem that a binary image is distorted due to a quantization error and an accurate gradation image cannot be generated.

Therefore, the present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a gradation image generation method which enables a display device to generate an easily viewable image at high speed with a small memory. To aim.

[0009]

In order to achieve the above-mentioned object, the present invention provides an area storage memory for expressing a display object figure in a grid-like pixel unit and storing the area of the pixel for each pixel, Vector data storage means for storing vector data for generating a display target graphic, and subjecting the vector data read from the vector data storage means to transformation processing such as enlargement or reduction as necessary. After that, an outline is interpolated by a straight line and / or a curve to output an outline, the area of a region to be filled inside the outline is stored in the area storage memory in pixel units, and the area value of the area storage memory is a gradation value. A gradation image generating method is provided, which is characterized in that gradation data of the display target graphic is generated by converting into a gradation image.

Further, in the gradation image generating method of the present invention, the outline is divided into minute straight lines, and the area of the shadow formed by the minute straight lines when the fine straight lines are viewed from a predetermined direction is shaded. The calculation is performed for each certain pixel, and the area of the shadow is added to or subtracted from the area value of the area storage memory corresponding to the pixel having the shadow, depending on the direction of the outline.

Further, the gradation image generating method of the present invention is characterized in that the fine line is generated by dividing the outline so as not to cross the boundary line of the grid-like pixels.

[0012]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a flowchart for explaining an embodiment of the present invention. Referring to FIG. 1, the embodiment of the gradation image generating method of the present invention comprises an area storage memory corresponding to each pixel of a reproduced image, and first, step S1
Then, initial settings such as setting parameters for modification processing such as enlargement and reduction of vector data and initializing the area storage memory to “0” are performed. Next, in step S2, it is determined whether or not the vector data to be processed exists in the vector data storage means. If the vector data exists, the process proceeds to step S3, and all the vector data is read. If there is no vector data, the process proceeds to step S5.

In step S3, modification processing such as enlargement, reduction, rotation, etc. is performed on the vector data consisting of the start and end points and the interpolation information, and the process proceeds to step S4. In step S4, the contour line is reproduced from the vector data after the transformation process and the area is calculated in pixel units, and the process returns to step S2.

In step S5, after the area calculation processing is completed for all the vector data, the area value of each pixel is converted into a preset gradation value, and then the whole processing is completed. To do. At this time, in order to remove the influence of the quantization error, the maximum value and the minimum value of the area value may be limited or the maximum value and the minimum value of the calculated gradation value may be limited as necessary. May be. Also,
Since the gradation image generally has lower brightness than the binary image, gradation correction may be performed on the calculated area value or gradation value. It should be noted that when two gradations (the gradation value is “0” or “1”) are given as the gradation values to be output, it is naturally possible to generate a binary image.

FIG. 2 is a flow chart for explaining in more detail the processing contents of contour line reproduction and area calculation in step S4 shown in FIG. Referring to FIG. 2, in step S41, it is determined whether the vector data is a straight line section or a curve section. Here, in the case of a straight line section, after performing the process of step S43, the process of step S4 ends. On the other hand, in the case of a curved section, step S
Proceed to 42. In step S42, the curved section is approximated by a plurality of straight lines, and the process of step S43 is performed for each straight line. After finishing the process for all the straight lines, the process of step S4 is finished.

In step S43, the contour straight line given in step S41 or step S42 is subjected to processing such as division of the contour straight line, area calculation, and writing to the area storage memory. It should be noted that, in step S4, the curve is processed by linear approximation, but in general, there are problems such as the calculation being complicated if the curve is left as it is and it is difficult to obtain an analytical solution. It is common to perform linear approximation processing.

FIG. 3 is a flow chart for explaining the details of the processing for dividing the contour line and calculating the area in step S43 shown in FIG. Referring to FIG. 3, in step S431, the contour straight line is divided at the intersection of the contour straight line given in step S41 or step S42 and the pixel grid line of the reproduced image to generate a minute straight line, and the process proceeds to step S432. When the processing for all the minute straight lines is completed, the processing of step S43 is completed.

In step S432, the area of the shadow formed by the minute straight line when viewed from a predetermined direction is calculated for each pixel having a shadow, and the flow advances to step S433. At this time, the shadow area of the pixel including the minute straight line (for example, the area value S1 shown in FIG. 5B) and the shadow area of the pixel having other shadows (also shown in FIG. 5B). Only the area value S2) need be calculated. In step S433, step S4
The area calculated in 32 is added to or subtracted from the area storage memory corresponding to the shaded pixel, and the process returns to step S431. It should be noted that whether to add or subtract is determined according to the direction of the contour line.

FIG. 4 is a diagram showing an example of a contour line,
FIG. 5 is a diagram showing an example of a minute straight line. Hereinafter, the processing content in step S43 will be described more specifically with reference to FIGS. 3, 4, and 5.

In step S431, the contour straight line given in step S41 or step S42 is the contour line shown in FIG.
If the reproduced image is within the range of one-valued pixels as shown in (a), the contour straight line is set as a minute straight line and the process proceeds to step S432.

On the other hand, when the contour line extends over the pixel grid line of the reproduced image as shown in FIG. 4B,
Divide at the intersection with the pixel grid line. For example, in the case of FIG. 4B, the contour line (x1, y1)-(x2, y2)
Is (xp1, yp1), (xp2, yp2), (xp
3, yp3) and (xp4, yp4) intersect the pixel grid line at four points, so that a minute straight line (x1, y1)-
(Xp1, yp1), (xp1, yp1)-(xp2,
yp2), (xp2, yp2)-(xp3, yp3),
(Xp3, yp3)-(xp4, yp4) and (xp
4, yp4)-(x2, y2) are sequentially generated, and the process proceeds to step S432. When there is no unprocessed straight line section, the process of step S43 ends.

In step S432, as shown in FIG. 5A, as a shadow of a minute straight line when viewed from a predetermined direction (for example, the negative direction of the X axis in the case of FIG. 5), FIG.
As shown in (b), the shadow area value S of a pixel including a minute straight line
1 and the shadow area value S2 of pixels having other shadows are calculated, and the process proceeds to step S433. In the case of FIG. 5,
Since a minute straight line exists in the pixel (xi, yi), the pixel (x
The area value S1 is calculated as the shadow area of i, yi), and the area value S2 is calculated as the shadow area of each pixel from pixel (xi + 1, yi) to pixel (xmax, yi).

In step S433, the pixel (xi, y
The area value S1 calculated in step S432 is added to or subtracted from the area storage memory corresponding to i). Further, the area value S2 calculated in step S432 is added to or subtracted from each area storage memory corresponding to the pixels (xi + 1, yi) to (xmax, yi). Here, when the vector data is counterclockwise, that is, when the left side with respect to the direction of the generated contour line is the filling direction, addition is performed when the contour line is in the positive direction of the Y axis, and the contour line is the Y axis. The subtraction is performed when going in the negative direction of.

In the above description, the negative direction of the X axis is used as the predetermined direction, but either the positive direction of the X axis, the negative direction of the Y axis, or the positive direction may be used. You may use. However, in this case, addition or subtraction to / from the area storage memory is properly used according to the filling direction determined by the direction of the vector data and the direction of the contour line.

[0026]

Next, in order to more specifically describe the above-described embodiment of the present invention, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 6 is a diagram showing an example of vector data used in an embodiment of the present invention. Hereinafter, a process of generating gradation data of a reproduced image using the vector data shown in FIG. 6 will be described.

The vector data shown in FIG. 6 (a) has a rotation direction in the counterclockwise direction, that is, the left side of the contour line is the filling direction under the coordinate system shown in FIG. 6 (b). It is assumed that the conversion at the time of image reproduction is 1 time (that is, the same size). Further, as the direction of the shadow, the shadow created when viewed from the negative direction of the X axis is used. In such a case, the calculated area value is added when the direction of the contour line goes in the positive direction of the Y-axis from the coordinate system and the direction of rotation of the vector data, and is calculated when going in the negative direction of the Y-axis direction. Area value will be subtracted.

Referring to FIG. 1, in step S1, the deformation parameter is set (1 time), and the area storage memory corresponding to each pixel of the reproduced image is secured and initialized (initial value "0").
I do. The description of other settings such as the setting of the storage location of the vector data to be read is omitted here. Note that FIG. 7A shows the contents of the area storage memory at the stage when step S1 is completed.

Referring to FIG. 1, in step S2, vector data is sequentially read from the vector data storage means, and the process proceeds to step S3. In step S3, the process of equal size is performed, and then the process proceeds to step S4.

Referring to FIG. 2, in step S41,
It is determined whether the vector data is a straight line section or a curved line section. In the case of the vector data shown in FIG. 6, since the section vectors P0P1, P1P2, and P4P5 are straight sections, the process directly proceeds to step S43. On the other hand, since the section vectors P2P3 and P3P4 are curved sections, they are linearly approximated in step S42 and divided by Bi (i = 1, 2, 3, ..., 6) as shown in FIG. It proceeds to step S43. As a result, in step S43, P0P1, P1P2,
P2B1, B1B2, B2B3, B3P3, P3B4,
The processes of B4B5, B5B6, B6P4, P4P5 (= P0) are sequentially performed.

Referring to FIG. 3, in step S431, it is checked whether or not the given contour line crosses the pixel grid line. As shown in FIG. 8, contour lines P0P1, B1B2,
Since B2B3, B4B5, and B5B6 straddle the pixel grid line, the intersections of the contour line and the pixel grid line (Qi (i = 1, 2, 3, ..., 7) in the case of FIG. 8) are calculated. It is divided into minute straight lines, and the process proceeds to step S432 sequentially. On the other hand, in the case of other contour straight lines, there is no need for division, and therefore the process proceeds directly to step S432.

Referring to FIG. 3, in step S432, the area of the shadow formed by each of the minute straight lines when viewed from the negative direction of the X-axis is calculated.
Proceed to 433. For example, as shown in FIG. 9A, in the fine straight line P0Q1, since the fine straight line overlaps the pixel grid line, the area value S11 of the shadow portion may be calculated for one pixel. Further, as shown in FIG. 9B, in the fine straight line P2B1, the area value S21 of the pixel including the fine straight line is
And the shadow area value S22 of the other shaded pixels are calculated.

Referring to FIG. 3, in step S433, the area value calculated in step S432 is added to or subtracted from the area storage memory corresponding to each pixel. For example,
In the case of FIG. 9A, since the direction of the contour straight line is the positive direction of the Y axis, the area value S11 is added to the area storage memory corresponding to each target pixel. That is, the area value of the area storage memory corresponding to each pixel is set to Gxy (x = 0, 1,
, 4, y = 0, 1, ..., 5), G11 = G11 + S11, G21 = G21 + S11, G31 = G31 + S11, G41 = G41 + S11.

On the other hand, in the case of FIG. 9B,
Since the contour line is in the negative direction of the Y-axis, subtraction is performed, and the calculation is performed as follows: G24 = G24-S21 G34 = G34-S22, G44 = G44-S22.

As described above, the final section vector P4
When the processing up to P5 is completed, step S shown in FIG.
Move to 5. FIG. 7B shows the contents of the area storage memory at the stage when step S4 ends. Last step S5
Then, the calculated area value is converted into the output gradation value.

Although one embodiment and one example of the present invention have been described above, the present invention is not limited to such an embodiment and example, and various modifications based on the principle of the present invention. including.

For example, as the area value, a value multiplied by a constant may be used. In this case, an integer memory can be used as the area storage memory. In addition, when a memory for storing the generated gradation image is provided in advance, the memory can be used as an area storage memory.

[0039]

As described above, according to the present invention,
Read vector data such as characters and figures, calculate the outline by interpolating with straight lines and curves, store the area of the area to be filled inside the outline in pixel units in the area storage memory, and use this area value as the gradation value. Since the gradation image is generated by converting to, it is not necessary to reproduce the binary image as in the conventional case, and the processing time can be shortened.
Work memory can be reduced.

Further, according to the present invention, the area value of the shadow formed by the fine straight line is calculated when viewed from a predetermined direction for each fine straight line, so that it is more accurate than the conversion from the binary image. The key value can be calculated.

Further, according to the present invention, if a value obtained by multiplying the area value by a constant is used and the memory for storing the gradation image can be used as the area storage memory, almost no work memory is required. Have advantages.

[Brief description of drawings]

FIG. 1 is a flowchart for explaining an embodiment of the present invention.

FIG. 2 is a flowchart for explaining in more detail the processing contents of contour line reproduction and area calculation according to the embodiment of the present invention.

FIG. 3 is a flowchart for explaining in more detail the processing contents of contour straight line division and area calculation according to the embodiment of the present invention.

FIG. 4 is a diagram showing an example of a contour line.

FIG. 5 is a diagram showing an example of a minute straight line.

FIG. 6 is a diagram showing an example of vector data used in an embodiment of the present invention.

FIG. 7 is a diagram showing the contents of the area storage memory immediately after initialization and at the end of processing in an embodiment of the present invention.

FIG. 8 is a diagram for explaining processing of straight line approximation of a curved section and division of a contour straight line according to an embodiment of the present invention.

FIG. 9 is a diagram for explaining a process of calculating an area of a shadow of a minute straight line according to an embodiment of the present invention.

FIG. 10 is a diagram for explaining an example of a conventional gradation image reproduction method.

[Explanation of symbols]

 P0, ..., P4 End points of straight line section or curved section B1, ..., B6 Point when curve section is linearly approximated Q1, ..., Q7 Point obtained by dividing contour straight line

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location H04N 1/407 H04N 1/40 101E

Claims (3)

[Claims] 1. An area storage memory for expressing a display target figure in a grid-like pixel unit and storing an area of the pixel for each pixel,
Vector data storage means for storing vector data for generating the display target graphic, and subjecting the vector data read from the vector data storage means to transformation processing such as enlargement or reduction as necessary. After that, an outline is interpolated by a straight line and / or a curve to output an outline, the area of the area to be filled inside the outline is stored in the area storage memory in pixel units, and the area value of the area storage memory is gradation. A gradation image generating method, characterized in that gradation data of the display target graphic is generated by converting into a value. 2. The outline is divided into minute lines, and the area of the shadow formed by the minute lines when viewed from a predetermined direction for each minute line is calculated for each pixel having a shadow, and there is a shadow. 2. The gradation image generating method according to claim 1, wherein the area of the shadow is added to or subtracted from the area value of the area storage memory corresponding to a pixel according to the direction of the outline. 3. The gradation image generating method according to claim 2, wherein the fine line is generated by dividing the outline so as not to cross the boundary line of the grid-shaped pixels.