JPS63249193A - Image data compression system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a compression method for image data containing characters, etc., and in particular, a method for approximating the outline of characters, etc. with a function curve or a set of straight lines,
The present invention relates to an image data compression method that compresses image data based on the contour specifying information.

[Prior Art] It is well known that the amount of dot data obtained by dividing image data such as characters into dots is extremely large.

Therefore, various data compression methods have been proposed in order to compress and store or transmit this large amount of data. One such data compression method is the so-called contour method.

[Problems to be Solved by the Invention] Linear approximation methods and n-th order curve approximation methods have already been proposed as data compression methods using the contour method, but the former linear approximation method does not guarantee contour smoothness. Furthermore, the latter n-dimensional curve approximation method has the disadvantage that it takes time to generate a curve.

Therefore, there is a method of using a cubic Bezier curve that generates a curve quickly, but this curve has the problem of being difficult to approximate.

The present invention has been made in view of the above-mentioned conventional example, and it is an object of the present invention to provide an image data compression method for approximating and encoding the outline of image data such as characters by curve approximation with a high generation rate.

[Means for Solving the Problems] In order to achieve the above object, the image data compression method of the present invention has the following configuration. That is, means for displaying line drawing information and specifying a straight line part and a curved part of the line drawing information, and means for calculating the slope and coordinates of the curved part at sections into which the curved part is divided or at both end points of the curved part. , means for determining dividing points within the section or on the curved section;
means for determining the coordinates of the dividing point; approximation means for approximating the curved section based on the slope of the curved section and the coordinates of the end points and the dividing point; and coordinates of a plurality of specific points of the approximated curve. and means for setting a code corresponding to the curve or section as an encoding code of the curve or section.

[Operation] In the above configuration, line drawing information is displayed, and the line drawing information is divided into straight parts and curved parts and specified. For a curved part, find the slope and coordinates of the curved part in the section where the curved part is divided or at both end points of the curved part, determine the dividing points within the divided section or on the curved part, and find the coordinates of those dividing points. . Next, the curved part is approximated by a curve equation based on the slope of the curved part and the coordinates of both end points and dividing points of the curved part,
It operates to compress image data by using codes corresponding to the coordinates of a plurality of specific points of the approximated curve as a curve or section encoding code.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Description of Functional Block Diagram (Fig. 1)] Fig. 1 is a block diagram showing the functional configuration of the embodiment.

In the figure, reference numeral 10 denotes an image data input unit that inputs image data that has been dot-decomposed into an [x, yl matrix, and is comprised of, for example, an image scanner. Reference numeral 11 denotes a contour extraction section that extracts the contours of image data such as characters inputted from the image data input section 10 and separated into dots. 12
1 is a straight/curved portion discriminating unit which displays the outline of a character or the like extracted by the outline extracting unit 11 on a display unit 20 such as a CRT display, and allows the operator to divide the outline into straight parts and curved parts. This is done by specifying a point on the outline using the digitizer 21, mouse, light ben, or the like.

The contour portion identified as a straight line is converted by the function determining unit 13 into a linear equation such as y=ax+b representing a straight line.

On the other hand, for the contour portion identified as a curve, the start point and end point are designated by the operator using the start point and end point designation section 14.

This instruction is also performed by pointing a point on the outline on the display using a light pen, digitizer, etc., as described above. Next, find a predetermined number of contour points that divide the curved section designated by the start point and end point, and calculate the contour (curve section) at both end points (start point, end point) from the average value of the slope with both end points (start point and end point). ) to find the slope.

In the point specifying section 15, the operator selects an appropriate point between the starting point and the ending point by specifying it using the digitizer 21, light ben, etc., as described above.

The cubic Bezier curve calculation unit 16 calculates a curve using a cubic Bezier curve equation based on the starting point, the ending point, and the points on the contour designated by the operator, and displays the curve on the display unit 20. The operator looks at the display and, if correction is necessary, instructs the correction section 17 again to specify a point.

If there is no need for correction in the correction unit 17, the coding unit 18 codes the coordinates of the four points adopted to obtain the curve using the Bezier curve, and codes the start and end points of the straight line part.
It is stored in the storage unit 19 as a compressed code.

Note that the decoding section 22 decodes the compressed code encoded by the encoding section 18 and converts it into coordinates and linear equations.

Based on this coordinate data, the curved part of the outline is obtained using the Bezier curve equation, and the straight part of the outline is synthesized to obtain the original outline of the character, etc.

The data IA filling of each part will be explained in detail below.

[Feature Extraction of Image Data (FIGS. 2 to 4)] The image data input unit 0 inputs image data by rask scanning using a scanner device, etc., and decomposes it into dots in the form of an [x, yl matrix. The binary dot pattern data thus obtained becomes the original image data to be processed.

The contour extraction unit 11 extracts from 0'', 1, or 1 to 0 in the X or y direction of the binary dot pattern data.
The dot position that changes to ” is extracted as a contour point.Second
The figure shows the contour data of the character ``ei'' obtained in this way.

The operator identifies a straight line part and a curved part of the contour data displayed on the display unit 20, for example as shown in FIG. 2, and indicates the starting point and end point of the straight part using the digitizer 21 or the like.

Figure 3 is a diagram showing the contour data identified in this way.
The solid line portion is a portion that the operator has identified as a straight portion, and the broken line portion is a portion that the operator has identified as a curved portion. The black circles at both ends of the straight line indicate the designated starting point or ending point. The straight line portions shown by these solid lines are converted into a linear equation by the function determining unit 13.

FIG. 4 is an enlarged view of portion 30 of FIG.

31 is a straight line portion identified as a straight line, and 32 and 33 are the starting point and end point of the straight line portion 31, respectively. When the dividing point 40 is input, the start point/end point indicating section 14 determines a curve 41 starting from point 32 and ending at 40, and a curve 42 starting from point 40 and ending at point 33.

[Calculation of slope of curve (Figs. 5 to 8)] Next, the slope at each point on the curve designated as a curved portion is calculated.

This method extracts a predetermined number of points before and after a point on a curve, calculates the slope of each line segment connecting the point and the points before and after it, and calculates the slope of the curve at a predetermined point.

Figure 5 is point P. 5 is a diagram showing a case where the slope to at a point Pa is determined when is the starting point of a curve 50. FIG.

Point Q1. Q2 is a point extracted on the contour to find the slope, and is a line segment P. The slope of Q+ is mo, the line segment Pa Q2
Let the slope of be ml. Line segment P. The slope mo of Ql is the coordinates of Po (X+, '/l), (1+ coordinates (x2, y
2), then x2 −x.

The slope mo is determined by Similarly, if the coordinates of Q2 are (x3, ys), then x3 -x.

becomes.

When the slope no and ml of each line segment are determined, the starting point P
The slope of 0 is obtained by

Note that the end point can also be obtained in the same manner.

FIG. 6 is a diagram showing the case where the slope t of the curve at the connection point PI between the curve 61 and the curve 62 (eg, point 40 in FIG. 4) is determined.

Here, the point Q−+ on the contour of each of curves 61 and 62
, Q+, and calculate the slope m-1 of the line segment Q-+P+ and the line segment P+
From the slope m of Q+, it can be found as follows.

's7 diagram is a song connected to straight line 71! This is a diagram showing the case where the slope t at the starting point P2 of the line 71 is calculated.The slope t2 at this time is equal to the slope mo of the straight line 71, and t,=m
It is represented by o.

FIG. 8 is a separate and enlarged view of the curve 41 in FIG. 4, and the same parts as in FIG. 4 are indicated by the same symbols.

In the figure, a point 80 is a point designated by the operator, and its coordinates are (xu, yu).

Add the coordinates of the starting point 32 to the curve 41 (Xor'jo)1 starting point 3
The slope of the curve at 2 is 70, and the coordinates of the end point 40 are (
X3. '/s)% The slope of the curve at the end point 40 is 1. shall be. If the division value of the point 80 is 0.5, the other two points 81 (x+, 3'l), 82 that specify the Bezier curve
(X2, y2)3'+-jo (XI-Xo)
“Y.

It is calculated by the formula V2=t+ (X2-X,)"Vs, and Pa (Xo, yo) l P 1(
XI, y+) I P2(X2y2), P3(X3
．． V3) Then, the curve is 0≦t≦1, and P +t+ -Pa (1-t)'÷3P+ (1-t
) 2t÷3P2 (1-t)t'+Pst'.

The Bezier equation calculated in this manner is displayed on the display section 20 as a dashed curve 83 in FIG.

The operator compares the curve 83 calculated above with the original curve 41, and if they do not match, moves the curve 80 on the curve 41 and repeats the Bezier calculation and display, so that the curve 83 and the curve 4 are
The above operation is repeated until the numbers 1 match.

[Explanation of coding (Figures 9 and 10)] Figure i9 (A
) is a diagram showing an example of a coded contour information format.

Here, as described above, the starting point coordinates of each sample section of the straight line and curved sections, the coordinates of the specific point of the approximate curve, and the end point coordinates are encoded and stored as a set of block data organized into each block. By doing so, it is possible to obtain compressed data that is faithful to the outline of image data such as arbitrary characters.

The block header 90 is an area for storing the number of sample points for one block, and the segment ladder 91 includes flags for distinguishing straight lines or Bezier curves, and flags for indicating the start and end of a line segment or curve. Segment information 9
2 encodes and stores the x and y coordinate values of the starting point, ending point, and each specific point.

FIG. 9(B) shows the case where the curve 41 of FIG. 8 is encoded and recorded.

The curve 41 is a part of the part indicated by 30 of the character "Ei" in FIG. 3, and the number of sample points of the part 30 is set in the block header 90. A flag indicating the starting point 32 of the curve 41 is set in the segment header 100 . That is, both the curve flag F93 and the starting point flag F94 are on. The segment information 101 stores a code that encodes the coordinates (xo, ya) of the starting point 32. The coordinates of specific points 81 and 82 on the curve 41 are stored in segment information 103 and 105, respectively, and only the curve flag is turned on in the corresponding segment headers 102 and 104. Also, the end point 40 of the curve 41 is the next curve 42
Since it is also the starting point of the segment header 106, the curve flag and starting point flag are turned on, and the segment information 107
The code of (X3+y3) is stored in .

Each block of data encoded in the above format is stored in units of blocks as shown in FIG. 10.

What has been described so far relates to character contour data compression, and next, a case will be described in which the contour data compressed in this manner is decoded into the original contour data.

For compressed data stored as shown in Figure 10, the segment head and segment information are read for each block data, and if the straight line flag of the segment header is on (straight line), the combined starting point and ending point are connected with a straight line. Reproduced. On the other hand, for those whose curve flag in the segment header is on (curve), O≦t≦1 using the Bezier curve formula described above from the decoded coordinates of the four specific points, P + t + = Po (1-t) ” 3P1t (1-t
) Find the curve using "3P2t2(1-t)"P3t'. At this time, the curve can be expressed by dividing t sufficiently finely between "O" and "1" and drawing each section with a straight line.

In this way, the reconstructed contour data is developed by a dot pattern in the image data storage section, and is supplied to an output device such as a laser beam printer or CRT, thereby reconstructing a desired character or image.

Note that in this example, a method of moving on the original curve was used to correct the input arbitrary point, but the input arbitrary point was fixed and the decomposition coefficient U was changed from "0" to "1". It can also be corrected by changing the value between ”.

As explained above, according to this embodiment, coding of contour lines using Bezier curves, which has been considered difficult in the past, can be done quickly and with good precision by specifying the start point, end point, and other points on the contour line. effective.

[Effects of the Invention] As described above, according to the present invention, the outline of image data can be easily encoded and reproduced (decoded) at high speed.

[Brief explanation of drawings]

Figure 1 is a functional block diagram of this embodiment. Figure 2 is a diagram showing the contour data of the input character "Mi". Figure 3 is a diagram showing the contour data of Figure 2 divided into straight and curved parts. Figure 4 is an enlarged view of a part of Figure N3. Figures 5 to 7 are diagrams each showing how to find the slope on the curve. Figure 8 is a part of the curve in Figure 4. Figure 9 (A) is a diagram showing an example of the format of contour information; Figure 9 (B) is an example of the contour information of the curve in Figure 8. A diagram showing an example: FIG. 10 is a diagram showing a format of block data. In the figure, 10... Image data input section, 11... Contour extraction section, 12... Straight line/curve section identification section, 13... Function determination section, 14... Start point, end point instruction section, 15... Point instruction unit, 16... Cubic Bezier curve calculation unit, 17...
Correction section, 18... Encoding section, 19... Storage section, 2
0...Display unit, 21...Digitizer, 22...Decoding unit. X Figure 2 Figure 3 Figure 4 Figure 8

Claims (3)

[Claims] (1) Means for displaying line drawing information and specifying a straight line portion and a curved portion of the line drawing information, and means for determining the slope and coordinates of the curved portion at sections into which the curved portion is divided or at both end points of the curved portion. a means for determining a division point within the section or on the curved section; a means for determining the coordinates of the division point; 1. A compression method for image data, comprising: approximation means for approximating; and means for using codes corresponding to the coordinates of a plurality of specific points of the approximated curve as an encoding code for the curve or section. (2) The image data compression method according to claim 1, wherein the line drawing information is contour information of input image data. (3) The approximation means performs curve approximation using a cubic Bezier curve, and stores the curve approximation as contour data of four specific points of the cubic Bezier curve. Image data compression method.