JPS6349821B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to bit reduction in the encoding of handwritten signals. The need for image information in recent communication systems and office equipment is rapidly increasing. Currently, facsimiles are often used to transmit image information. Naturally, when using a facsimile, you must prepare the letters and figures you want to send in advance. On the other hand, there may be information that you would like to convey to the other person while writing it on the spot, depending on the needs of the situation, or for supplementary explanation during a conversation. The system used in such cases is a handwriting input device such as a tablet.
Handwritten signal transmission systems consisting of handwritten signal display devices such as CRT displays have been proposed (e.g., “Teleboard, Scribophone and
Their Relation to Coded Text Transmission”
A paper entitled (Miinchener Kreis
conference record, June, 1978) etc.). In such systems, it is often necessary to send handwritten signals simultaneously with audio signals and other signals, so band compression of handwritten signals is extremely important. An example of a handwritten signal transmission system is shown in FIG. The sending side includes a tablet 10 and a stylus 20.
The handwritten signal input device includes a coordinate detection circuit 30 and an encoder 40. The receiving side includes a decoder 50 and an interpolation circuit 60 for interpolating between sample values.
It is composed of a CRT display device 70.
On the transmitting side, the position of the stylus 20 is output from the coordinate detection circuit as information on the horizontal axis (X coordinate) and vertical axis (Y coordinate) on the tablet 10. Since such a device is already widely known, a detailed explanation will be omitted. The principles of tablets are explained in an article entitled "Current status and history of data tablets, which are being actively researched and developed" (Nikkei Electronics, November 19, 1973 issue).
P.79-93) etc. The output of the coordinate detection circuit, that is, the signal representing the position information of the stylus may be either analog or digital. The position information is input to an encoder 40 and transmitted as a digital signal. The frequency component included in the handwritten signal can be considered to be at most 15Hz, so
Location information is sampled at around 30Hz. now,
The resolution of both the X and Y coordinates is 1/2000 of the total length.
If so, each coordinate can be represented by an approximately 11-bit digital signal. However, as it is, the number of bits per second is 660 (11 x 2 x 30). It has been reported that if a part of the coordinate signal is expressed using a difference (difference with the coordinates of one sample before), it will be approximately 200 bits/second (a paper entitled "A Study of Handwritten Signal Coding Methods"). (IEICE Communication Method Study Group Material CS80-64)). However, if we consider human hand movements, the number of bits can be further reduced. Further, by further reducing the number of bits of the handwritten signal, the flexibility of the handwritten signal transmission system will be greatly increased, and the possibility of improving services can be expected. An object of the present invention is to provide a handwritten signal encoding device that reduces the number of bits in encoding without degrading the quality of the handwritten signal. According to the present invention, there is provided a control section which inputs a signal for displaying the up-down of a pen on a tablet and outputs a control signal, and inputs an X coordinate and a Y coordinate and adjusts the two coordinates and each of them according to the control signal. A handwritten signal encoding device is obtained that includes a difference circuit that takes a difference from a predicted value and a coordinate conversion circuit that transforms the output of the difference circuit into polar coordinates. In order to encode handwritten signals, it is necessary to fully understand the properties of handwritten signals. Roughly speaking, handwritten signals can be thought of as a combination of short straight lines and circular arcs. FIG. 2 shows the sampling when the alphabet "B" is written by hand. The sampling frequency is 30Hz. The small circles in the figure indicate sampling points, and the numbers indicate their order. 1 to 5
It is almost a straight line from 6 to 11, and although it is slightly distorted, it can be considered as one arc. Also, 11 to 16
It can also be considered an arc. Considering the inertia of the human hand and pen, it is natural that the interval between sampling points becomes shorter near the start and end points of a straight line or arc. Considering the above-mentioned properties of handwritten signals, it becomes easy to understand the encoding method according to the present invention. 3 and 4 are block diagrams illustrating a first embodiment of an encoder 40 and a decoder 50 according to the present invention. The input signals of the encoder 40 are a signal X _i representing the X coordinate, a signal Y _i representing the Y coordinate, and a signal Z _i representing whether the stylus is in contact with the tablet. Both are output from the coordinate detection circuit 30. It is assumed that X _i and Y _i are each 11-bit digital signals. Z _i is a 1-bit digital signal that is 1 when the stylus is in contact with the tablet;
In other cases, it is 0. FIGS. 5 and 6 are block diagrams showing one embodiment of a differential circuit and an integral circuit using the first embodiment. FIG. 7 is an example of input coordinate information. The circles from 1 to 5 represent sampled coordinate information. At these points, the stylus is in contact with the tablet (pen down), that is, Z =
It is 1. At other points, Z=0. The two straight lines on the left and bottom of Figure 7 are the X axis and the Y axis.
The above description is for convenience of indicating the axes. The intersection of the X and Y axes is the coordinate origin 0. First, explanation will be given using FIGS. 3 to 7. 1st
The coordinate information of point 1 X ₁ ,
Y ₁ and Z ₁ are input. Here, X ₁ is the X coordinate of the stylus, Y ₁ is the Y coordinate, and Z ₁ is the pen down (Z ₁ =
1). The control circuit 41 knows that the stylus has touched the tablet because the signal _Z1 is applied to the Z input, and the difference circuits 42, 43, 4
Clear the contents of registers 5 and 46. All of these differential circuits have the configuration shown in FIG. The i-th input signal T _i to the difference circuit 80 is input to the subtracter 83 and the register 81 . When the signal T _i is input, the input signal T _i-1 of one sample before appears at the output of the register 81, and the multiplier 82
The predicted value α·T _i-1 is created by multiplying by the constant α. The subtracter 83 receives the input signal T _i and the predicted value α・
T _i-1 is input. Therefore, the output of the subtractor 83
U _i becomes U _i =T _i −α・T _i-1 . Good characteristics can be obtained by setting α=0.8, but it is easiest to set α=1 (multiplier 82 is not required). To simplify the hardware, α=1
It is better to In the following explanation, it is assumed that α=1.
For T _i and U _i in FIG. 5, when the register 81 indicating the input and output of each differential circuit is cleared, the output of the register 81 becomes 0, and the output U _i of the differential circuit 80 becomes T _i . Therefore, when the first samples X ₁ and Y ₁ are input, the internal registers of the difference circuits 42 and 43 are cleared, and the outputs of both difference circuits become X ₁ and Y ₁ . The control circuit 41 receives the first samples X ₁ and X ₂
A set signal is output to the differential circuits 42 and 43 before the signal disappears. Signals X ₁ and Y ₁ are stored in registers inside difference circuits 42 and 43. second sample
When X ₂ and Y ₂ are input, X ₁ and X ₂ become predicted values, and the outputs △X ₂ and △Y ₂ of the difference circuits 42 and 43 are △X ₂ = X ₂ −X ₁ △Y ₂ = Y ₂ −Y ₁ . In this way, a difference signal appears at the outputs of the difference circuits 42 and 43 from the second sample onwards. The difference signals ΔX ₂ and ΔY ₂ are applied to the coordinate transformation circuit 44. The coordinate conversion circuit 44 converts the information of ΔX ₂ and ΔY ₂ into an angle θ ₂ and a distance r ₂ as shown in FIG. Here, when the i-th sample is input, the angle θ _i and the distance r _i are θ _i = tan ^-1 (△Y _i / △X _i ) r _i =√(△ _i ) ² + (△ _i ) ² becomes. Outputs θ _i and r _i of the coordinate conversion circuit 44 are input to difference circuits 45 and 46. second sample
When the difference between X ₂ and Y ₂ is coordinate transformed to obtain θ ₂ and r ₂ , the control circuit 41 clears the difference circuits 45 and 46 . The difference circuits 45 and 46 output θ ₂ and r ₂ . The control circuit is designed so that before θ ₂ and r ₂ disappear,
A set signal is output, and θ ₂ and r ₂ are stored in the registers inside the differential circuits 45 and 46. Therefore, when the third and subsequent samples are input, the outputs of the difference circuits 45 and 46 are the differences between the signals θ _i , r _i and the predicted values θ _i-1 , r _i-1 Δθ _i = θ _i −θ _i-1 Δr _i =r _i −r _i-1 is obtained. The multiplexer 47 is a circuit for sequentially outputting control information and coordinate information, and is a circuit for sequentially outputting control information and coordinate information.
controlled by According to the example of FIG. 4, when the first samples X ₁ and Y ₁ are input, the multiplexer outputs a control signal I ₁ =1 indicating the beginning of a stroke, and then X ₁ and output Y ₁ . When the second sample and subsequent samples are input, the control signal I _i =0 indicating the second and subsequent samples and the outputs of the difference circuits 45 and 46 are sequentially selected and output. The input signals, the outputs of each circuit, and the output of the multiplexer 47 are summarized as shown in Table 1.

【table】

Claims (1)

[Claims] 1 A control section that inputs a signal to display the up-down of the pen on the tablet and outputs a control signal, and
A handwritten signal code having a difference circuit which inputs a coordinate and a Y coordinate and calculates the difference between the two coordinates and their predicted values according to the control signal, and a coordinate conversion circuit which converts the output of the difference circuit into polar coordinates. conversion device.