JP2625452B2 - Image data encoding and decoding methods - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for efficiently encoding and decoding a series of coordinate values representing a drawn image such as a handwritten character or a graphic.

(Prior Art) Conventionally, an electronic blackboard device equipped with a digitizer and a tablet having the same principle as the digitizer has been configured to sequentially detect and output a series of coordinate values representing a drawn image of a handwritten character or a figure. I was

When a video conference system or the like is configured using the digitizer or the electronic blackboard device, it is necessary to transmit the obtained series of coordinate values in real time via a telephone line or the like.

At this time, the series of coordinate values can be transmitted as they are, but the amount of data to be transmitted becomes enormous, and particularly when an inexpensive and low-speed modem is used, the time required for transmission becomes longer. Was compressed and transmitted.

As a conventional data compression method of this type, there has been a difference method.

This is because the transmitting side calculates the difference between the coordinate value (previous coordinate value) obtained at the previous coordinate detection and the coordinate value obtained at the last two coordinate detections, and calculates the difference and the previous coordinate value. Is calculated as the coordinate value of the predicted point, and the error between the coordinate value of the predicted point and the actually obtained coordinate value is encoded and transmitted. And the error obtained by decoding the received data is added to reproduce the actually obtained coordinate value.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional method, for an image based on constant velocity linear motion, for example, for a straight line drawn with a ruler on a plate surface, a coordinate value of a predicted point and an actual coordinate value Error is small, and effective data compression can be achieved.However, there are few images based on constant velocity linear motion in actual drawn images, and therefore, in practice, a very large data compression effect is not obtained. When large errors are continuously obtained, such as when a marker is quickly moved and drawn on a wide board of an electronic blackboard device, there has been a problem that data transmission is significantly delayed and real-time performance is impaired.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image data encoding and decoding method capable of eliminating the above-mentioned problems, obtaining a prediction point with a small error, and efficiently compressing the image data.

(Means for Solving the Problems) FIG. 1 shows an outline of an image data encoding method according to the first invention of the present application, in which a coordinate value immediately before a current coordinate value (hereinafter referred to as a preceding coordinate value). Difference calculating means 1 for calculating a difference between the previous coordinate value (hereinafter referred to as the coordinate value before the previous one).
A first predicted point calculating means 2 for calculating the coordinate value of the first predicted point by adding the difference and the previous coordinate value;
A difference difference calculating means 3 for calculating a difference from the immediately preceding difference (hereinafter referred to as a difference difference), and adding the difference difference and the coordinate value of the first prediction point to obtain the coordinate value of the second prediction point. A second prediction point calculating means 4 for calculating; an error calculating means 5 for calculating an error between the current coordinate value and the coordinate value of the second prediction point; and an encoding means 6 for encoding the error. FIG. 2 shows an outline of a decoding method for image data according to the second invention of the present application, in which a decoding means 7 for decoding encoded data to obtain an error, and a difference between a preceding coordinate value and a preceding coordinate value. , A first prediction point calculation means 2 for adding the element and the previous coordinate value to calculate a coordinate value of the first prediction point, and a difference between the difference and the immediately preceding difference. A difference difference calculating means 3 for calculating a difference difference between the first prediction point and a second difference value for calculating a coordinate value of the second prediction point by adding the difference difference and the coordinate value of the first prediction point. A measuring point calculation unit 4 consists of a coordinate value calculating means 8 which adds the coordinate value and the error of the second predicted point obtains the current coordinate values.

(Operation) In the first invention, the difference calculating means 1 calculates a coordinate value to be transmitted from a series of coordinate values input from an image input device (not shown), that is, a coordinate value before and a coordinate value before the current coordinate value. Is calculated, and this is calculated by the first prediction point calculation means 2.
And to the difference calculating means 3.

The first prediction calculation means 2 adds the difference and the previous coordinate value to calculate the coordinate value of the first prediction point, and sends it to the second prediction point calculation means 4.

The difference difference calculating means 3 calculates a difference difference between the difference and the immediately preceding difference (that is, the difference between the two-preceding coordinate value and the immediately preceding coordinate value), and calculates the difference between the difference and the second predicted point calculating means. 4

The second prediction point calculation means 4 adds the coordinate value of the first prediction point and the difference difference, calculates the coordinate value of the second prediction point, and sends it to the error calculation means 5.

The error calculating means 5 calculates an error between the current coordinate value and the coordinate value of the second prediction point, and sends it to the encoding means 6.

The encoding means 6 encodes the error according to a preset rule to form encoded data.

In the initial state, the previous coordinate value and the coordinate value before the previous coordinate value are set to the current coordinate value, that is, the same as the first coordinate value,
The difference and the immediately preceding difference are both set to zero.

Further, in the second invention, assuming that the encoded data corresponding to the current coordinate value is immediately before being input to the decoding means 7, it is calculated by the coordinate value calculating means 8 in the same manner as the current coordinate value described later. The previous coordinate value and the previous coordinate value are supplied to the difference calculating means 1 and the first predicted point calculating means 2,
With these, the difference, the difference difference, the coordinate value of the first predicted point, and the coordinate value of the second predicted point are calculated in the same manner as described above, and the coordinate value of the second predicted point is sent to the coordinate value calculating means 8.

The decoding means 7 decodes the encoded data, converts it into an error, and sends it to the coordinate value calculating means 8.

The coordinate value calculation means 8 adds the error and the coordinate value of the second prediction point to calculate a current coordinate value.

The coordinate values are sent as image data and sent to the difference calculation means 1 and the first prediction point calculation means 2 to be used for calculating the coordinate values of the next second prediction point.

In the initial state, both the previous coordinate value and the before-last coordinate value are set to be the same as the first coordinate value, and both the difference and the immediately preceding difference are set to 0.

(Embodiment) FIG. 3 shows one embodiment of an image data processing apparatus to which the method of the present invention is applied.
Denotes an image processing device, 13 denotes an encoding device, 14 denotes a decoding device, 15 denotes a transmission device, 16 denotes a data line, 17 denotes a display device, and 18 denotes an output device.

The image input device 11 is, for example, a digitizer or an electronic blackboard device. The image input device 11 converts the coordinate values of points (sample points) obtained by sampling a drawn image of a handwritten character, a figure, or the like at regular time intervals. Send to 13 sequentially.

The encoding device 13 converts the coordinate values into encoded data as described later, and sends the encoded data to the transmission device 15.

The transmission device 15 is, for example, a modem or the like, modulates the coded data, and sends it to another similar image data processing device via a data line 16 such as a telephone line.

On the other hand, data transmitted from another similar image data processing device via the data line 16 is demodulated by the transmission device 15, becomes encoded data, and is transmitted to the decoding device 14.

The decoding device 14 decodes the coded data into a series of coordinate values by the reverse procedure of the coding, and sends the data to the image processing device 12.

The image processing device 12 forms an image based on the coordinate values input from the image input device 11 or the decoding device 14, and
And a hard copy by an output device 18 such as a plotter if necessary.

The image input device 11 actually outputs data indicating various commands in addition to the coordinate values, but these are sent to the image processing device 12 and the encoding device 13 as they are.

Next, the manner of encoding in the encoding device 13 will be described in detail.

FIG. 4 shows a hardware configuration when the encoding device 13 is constituted by a microprocessor. In the drawing, reference numeral 21 denotes a central processing unit (CPU), 22 denotes a read-on memory (ROM), 23
Is random access memory (RAM), 24 is input port, 2
5 is an output port and 26 is a bus.

A program according to the flowchart shown in FIG. 5 is built in the ROM 22, and a work area X is stored in the RAM 23.
i, Yi, Yi−1, Yi−1, AXi, AYi, dXj, dYj, dXj−1 and dYj−
1 is set.

FIG. 6 shows an example of a drawn image in the image input device 11, in which 30 is the locus of the drawn image, and P0, P1, P2,.
3, Pk-2, Pk-1, Pk, Pk + 1,... PN indicate sample points obtained by sampling the trajectory 30 at fixed time intervals.

Each of the sample points Pn (where n = 0, 1, 2,..., K−3, k−2, k
-1, k, k + 1,... N) in the x and y directions (Xn,
Yn) are sequentially input from the image input device 1 via the input port 24.

When the coordinates (X0, Y0) of the first sample point P0 are input,
The work area in the RAM 23 is defined as Xi = Xi-1 = X0, Yi = Yi-
1 = Y0, dXj = dYj = 0 and dXj-1 = dYj-1 = 0, and the coordinate values (X0, Y
0) (hereinafter, this is referred to as a whole coordinate value) is output as it is.

The following processing is performed on the second and subsequent arbitrary sample points Pk (Xk, Yk).

First, the work areas dXj−1 and dYj−1 are stored in the work areas dXj−1 and dYj−1.
j, dYj data is stored as it is, and the work area dXj, dYj
And the difference between the work areas Xi, Yi and Xi−1, Yi−1, that is, dXj = Xi−Xi−1 (1) dYj = Yi−Yi−1 (2), and the work area Xi− 1, Work area X on Yi-1
i, Yi data is stored as is, and the work area AXi, AYi
And the sum of the work areas Xi−1, Yi−1 and dXj, dYj, that is, AXi = Xi−1 + dXj (3) AYi = Yi−1 + dYj (4), and a new work area Xi, Yi. Data Xk and Yk.

At this time, the work area Xi-1 and Yi-1 have 1
The coordinate values (Xk-1, Yk-1) of the immediately preceding sample point Pk-1 are stored, and the work areas AXi, AYi have the coordinate values (AXk, AXk) of the first prediction point APk corresponding to the sample point Pk. AYk) is stored, and the work areas dXj and dYj store the sample points Pk-1 and the differences dXi and dYi between the sample points Pk-2 immediately before the sample points Pk and the work areas dXj-1. , dXj-1 contains the sample Pk-2
And the difference dX2, dY2 between the sample point Pk−3 before the sample point Pk
Is stored.

Next, the data of the work areas dXj, dYj and dXj−1, dYj−1, that is, the differences aX, aY of dX1, dY1 and dX2, dY2 are obtained, and aX = dXj−dXj−1 = dX1−dX2 (5) AY = dYj−dYj−1 = dY1−dY2 (6) The data of the difference difference aX, aY and the work area AXi, AYi, that is, the sum of AXk, AYk is taken, and the second prediction corresponding to the sample point Pk is taken. Point B
Find the coordinate value (BXk, BYk) of Pk.

BXk = AXi + aX = AXK + aX (7) BYk = AYi + aY = AYK + aY (8) The coordinate value (BXk, BYk) of the second prediction point BPk is the coordinate value of the final prediction point with respect to the sample point Pk. In FIG.
It can be seen that the second prediction point BPk is closer to the sample point Pk than the first prediction point APk.

Further, the coordinate value (Xk, Yk) of the sample point Pk and the second prediction point B
From the coordinate value of Pk (BXk, BYk), the following error (ΔXk, Δ
Yk).

ΔXk = Xk−BXk (9) ΔYk = Yk−BYk (10) Next, the error (ΔXk, ΔYk) is encoded as described below.

First, it is determined which of the following four ranges the magnitude of the error (ΔXk, ΔYk) belongs to.

I) -2 ≦ ΔXk ≦ 2 and −2 ≦ ΔYk ≦ 2 II) (-2> ΔXk or ΔXk> 2) and (-2> ΔYk or ΔYk> 2) and (−4 ≦ ΔXk ≦ 4 and −4 ≦ ΔYk ≦ 4) III) (−4> ΔXk or ΔXk> 4) and (−4> ΔYk or ΔYk> 4) and (−8 ≦ ΔXk ≦ 8 and −8 ≦ ΔYk ≦
8) IV) (−8> ΔXk or ΔXk> 8) and (−8> ΔYk or ΔYk> 8) FIG. 7 shows the above ranges I to IV.
Is a prediction point, 32 is a dot range belonging to range I, 33 is a range II
The dot range belonging to the range III is a dot range belonging to the range III, and the dot range belonging to the range IV corresponds to a portion (not shown) outside the dot range.

 Encoding differs depending on the range.

First, encoding of range I (hereinafter, referred to as mode I encoding) will be described.

FIG. 8 (a) shows the correspondence between the dots in the range I in the mode I encoding and the numbers indicating their positions. In the figure, x indicates the dot at the prediction point, and ● (black circle) and ○ ( (White circles) indicate dots within the range I with respect to the prediction points. Here, numbers 0 to 24 assigned to the dots indicate the positions of the dots. Also, ● indicates a dot that is coded in 4 bits, and ○ indicates a dot that is coded in 6 bits.

In the actual encoding, a number m indicating the position of the sample point Pk is obtained from the following equation (11) based on the errors ΔXk and ΔYk, and m = (ΔYk + 2) · 5 + (ΔXk + 2) (11) The corresponding code is output according to the encoding table shown in FIG. 9 (a). In FIG. 9A, codes "1010" and "1011" are used as identification codes of ESC1 and ESC2 described later, and code "111111" is used as a flag (start) described later.

Next, encoding of the range II (hereinafter, referred to as mode II encoding) will be described.

FIG. 8 (b) shows the correspondence between the dots in the range II and the numbers indicating their positions in the mode II encoding. In the figure, x indicates the dot at the prediction point, and o indicates the dot at the prediction point. Show dots in range II. Here, the numbers 0 to 80 assigned to each dot indicate the position of each dot.

However, here, since it is not necessary to perform encoding within the encoding range in the mode I, the numbers 20 to 24, 29 to 33, 38
There is no need to encode dots corresponding to ~ 42,47 ~ 51,56 ~ 60. Therefore, the total number of points that actually need to be coded is 81-25 = 56, and can be coded with a 6-bit code.

In the actual encoding, a number m indicating the position of the sample point Pk is obtained from the following equation (12) based on the errors ΔXk and ΔYk, and m = (ΔYk + 4) · 9 + (ΔXk + 4) (12) The corresponding code is output according to the encoding table shown in FIG. 9 (b). However, in this case, in order to distinguish it from the 6-bit code in Mode I, the above-described ESC1 identification code is added before the output and output.

Next, range III and encoding (hereinafter, referred to as mode III encoding) will be described.

FIG. 8 (c) shows the correspondence between the dots in the range III and the numbers indicating their positions in the mode III encoding. In the figure, x indicates the dot at the prediction point, and ○ indicates the dot at the prediction point. Shows dots within range III. Here, numbers 0 to 288 assigned to each dot indicate the position of each dot.

However, here, since it is not necessary to perform encoding within the encoding range in the modes I and II, the numbers 72 to 80, 89
~ 97,106 ~ 114,123 ~ 131,140 ~ 148,157 ~ 165,174 ~ 182,
The dots corresponding to 191 to 199 and 208 to 216 do not need to be encoded. Therefore, the total number of points that need to be actually encoded is 289−81 = 208, and it is possible to encode with an 8-bit code.

In actual encoding, a number m indicating the position of the sample point Pk is obtained from the following equation (13) based on the errors ΔXk and ΔYk, and m = (ΔYk + 8) · 17 + (ΔXk + 8) (13) The corresponding code is output according to the encoding table shown in FIG. 9 (c). However, in this case as well, in order to distinguish it from the codes of other modes, the above-mentioned ESC2 identification code is added before the output and output.

It should be noted that for the range IV, encoding is disabled, a flag (end) is output, and the initial state is returned.

FIG. 10 (a) shows an overview of the entire encoded data of one frame (256 bytes or less) outputted from the output port 25, which is constituted by the above-mentioned encoding process. (Start), C is a control byte, X0 and Y0 are absolute coordinate values of the first sample point, D is data encoded for the second and subsequent sample points, and fb is a flag (end).

FIG. 10 (b) shows a part of the data D in detail. In FIG. 10 (b), the 4-bit code and the 6-bit code indicate the coding codes according to the mode I, and 6 bits following the ESC1 identification code. The bit code indicates the encoded code according to the mode II, and the bit code following the ESC2 identification code indicates the encoded code according to the mode III.

Usually, the coordinate values from pen down to pen up are composed of one or more frames. Mode I
V, that is, if encoding is impossible, data up to immediately before is 1
One frame is formed, and the subsequent data is incorporated into a new frame.

Since the decoding process is the reverse process of the encoding process, if the encoding process is performed in a reverse procedure, the errors ΔXk and ΔYk can be obtained from the encoded data. Coordinate values can be calculated.

(Effects of the Invention) As described above, according to the present invention, the difference between the previous coordinate value and the coordinate value before the previous coordinate value, that is, the speed in the drawn image is calculated for a series of image data such as handwritten characters and figures. In addition, the difference between the difference and the immediately preceding difference, that is, the acceleration in the drawn image is calculated, and the coordinate value of the prediction point is calculated based on the difference. Since the coordinate values of the points can be obtained, and the error between the coordinate values of the predicted points and the actual coordinate values is coded, the data amount can be efficiently compressed, and the communication function can be improved. There is an advantage that a large amount of data can be transmitted in real time when used in an electronic blackboard device provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of an image data encoding system of the present invention, FIG. 2 is a diagram showing an outline of an image data decoding system of the present invention, and FIG. FIG. 4 is a diagram showing an embodiment of a processing device, FIG. 4 is a diagram showing a hardware configuration of an encoding device, FIG. 5 is a flowchart of processing in the encoding device, FIG. FIG. 7 is a diagram showing a coding range, FIGS. 8 (a), (b) and (c) are diagrams showing correspondences between dots in the coding ranges I, II and III and numbers indicating their positions, respectively. FIGS. 10 (a), 10 (b) and 10 (c) show the correspondence between dot positions and codes in modes I, II and III, and FIG. 10 (a) shows an overview of the encoded data of one frame. FIG. 10 (b) is a diagram showing a part of the data D in detail. 1... Difference calculating means, 2... First predicted point calculating means, 3.
... Difference difference calculation means, 4 ... Second prediction point calculation means, 5 ...
Error calculating means, 6 ... coding means, 7 ... decoding means,
8 ... Coordinate value calculating means.

Claims (6)

(57) [Claims] An image data encoding / decoding system for encoding / decoding image data composed of a series of coordinate values representing a drawn image of a handwritten character, a figure, or the like, in a coding system preceding a current coordinate value. Difference calculating means for calculating a difference between a value (preceding coordinate value) and a coordinate value immediately before (coordinate value before two), and calculating the coordinate value of the first prediction point by adding the difference and the preceding coordinate value A first prediction point calculation unit that calculates a difference between the difference and the immediately preceding difference (difference difference); a difference calculation unit that calculates a difference between the difference and a coordinate value of the first prediction point. Second prediction point calculation means for calculating the coordinate value of the second prediction point; error calculation means for calculating the error between the current coordinate value and the coordinate value of the second prediction point; encoding means for coding the error And a coding method for image data. 2. A method for determining whether an error belongs to one of a plurality of predetermined ranges. If the error is included in the smallest range, a code corresponding to the code sequentially assigned to all positions in the range is determined. If the code is included in a range other than the smallest range, the code is converted to a corresponding code among codes sequentially added to each position except for a portion included in a smaller range within the range, and the code is 2. The image according to claim 1, further comprising: an encoding unit that adds an identification code immediately before the code to indicate which of the plurality of ranges corresponds to the code. Data encoding method. 3. The image data according to claim 2, wherein the size of each of the plurality of ranges is set such that the larger the range is, the larger the difference from the one smaller range is. Encoding scheme. 4. The image data encoding method according to claim 3, wherein the number of bits of a code sequentially assigned to each position in one range is reduced as the range becomes smaller. 5. An image data encoding and decoding method for encoding and decoding image data consisting of a series of coordinate values representing a drawn image of a handwritten character, figure, or the like, wherein an error is obtained by decoding the encoded data. Decoding means; difference calculating means for calculating a difference between the immediately preceding coordinate value (previous coordinate value) and the immediately preceding coordinate value (two-preceding coordinate value); A first prediction point calculation unit that calculates a coordinate value of the first prediction point by adding the value to the first prediction point; a difference difference calculation unit that calculates a difference (difference difference) between the difference and the immediately preceding difference. Second prediction point calculating means for calculating the coordinate value of the second prediction point by adding the difference difference and the coordinate value of the first prediction point; and adding the coordinate value of the second prediction point and the error to obtain the current coordinate. And a coordinate value calculating means for obtaining a value. 6. A method for determining whether or not an identification code is present immediately before a code. If there is no identification code, the identification code corresponds to a position designated by the code in the smallest range among a plurality of preset ranges. A decoding unit for converting the error into an error and, if there is an identification code, converting the error into an error corresponding to a position designated by the code within a range specified by the identification code among a plurality of preset ranges. 6. A method for reconstructing image data according to claim 5, wherein: