JPS634993B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an automatic line density switching control system in which the sub-scanning line density is automatically switched in order to change the resolution according to the density of an image in a two-dimensional encoding type facsimile apparatus. Regarding, especially
This paper relates to an automatic line density switching control method that performs density determination based on the number of vertical mode encodings in a facsimile machine that applies the two-dimensional encoding method of CCITT Recommendation T.4.

In facsimile image transmission, one method for achieving high image quality and high speed transmission is to switch the sub-scanning line density according to the density of the image, with standard resolution for coarse areas and high resolution for dense areas. Read/record. There is a variable linear density switching method.
This method counts the points at which white or black pixels change within a certain range, determines density, and switches the sub-scanning line density for reading or recording the next line.

This conventional method requires an image information change point counter to be provided separately from the image information compressor/decompressor. In addition, since the number of change points within a certain range on each line is used as the criterion for line density switching, even if the currently encoded line has little change visually compared to the line immediately before it, the number of change points If there are many numbers, it is determined that the density is high, and scanning is performed at a high resolution line density, which adversely affects the transmission time and causes problems.

The present invention aims to solve the above-mentioned problems, and therefore compresses or restores image information using a two-dimensional encoding method, and on the transmitting side, the image information of the encoded line is divided into In a facsimile device, image signals are compressed or When performing restoration, the vertical mode code for a certain encoded line is
Count V _L and V _R , compare the counted value with a predetermined reference value, and if the counted value is larger than the reference value, it is considered dense, and on the other hand, the counted value is the reference value. If the density is smaller than that, the density of the image is determined to be coarse, and the sub-scanning line density is sequentially switched in order to change the resolution based on the result of the determination.

Seriously, let's briefly explain the conventional linear density automatic switching control method.

FIGS. 1a and 1b are schematic diagrams of a conventional automatic selection method.

FIG. 1a shows the transmitter section, in which the read data signal of the facsimile transmission image read by the read controller 1 is transmitted to the data compressor 2 and the change point calculator 3.
given to. The data compressor 2 encodes the data according to a predetermined data compression method and sends it to the line via the modem 4. On the other hand, the change point counter 3 counts the number of change points in the read data, and when the change point count value in a certain range of the main scanning line is larger than a predetermined reference value, it is determined that the image being read has small changes. The determination is made, and the line density switch 5 outputs a line density instruction signal to the reading controller 1 to reduce the feed width of the sub-scanning line. The linear density counter 3 is
It operates completely independently of the data compressor 2, and is composed of an asynchronous counter or the like that is counted at the leading or trailing edge of an input pulse. Counter 3
is constructed such that it produces an output signal when a reference count value is reached within a certain time period related to the main scanning time, and is otherwise cleared. Next, FIG. 1b shows the receiver section. The facsimile signal received via the modem 6 is restored to the original image information signal by the data restorer 7. This restored signal corresponds to the read data signal output from the read controller 1 in FIG. 2a. Based on this restoration signal, the change point counter 8 and the linear density switch 9 operate in exactly the same way as in case a above, and send a linear density instruction signal to the recording controller 10 to control switching of the linear density. to make it possible to reproduce the original image.

As described above, in the conventional system, it was necessary to provide a dedicated change point counter for both transmission and reception.

Next, the present invention will be explained in detail.

The present invention improves the shortcomings of the conventional method by utilizing the two-dimensional encoding (modified read) method according to CCITT Recommendation T.4, and enables faster and clearer facsimile image transmission. This is to realize the following.

The two-dimensional encoding method according to Recommendation T.4 is based on the position of each changing pixel on the line currently being encoded.
This is a sequential encoding method in which encoding is performed by referring to the position of a corresponding reference pixel on an encoding line or a reference line immediately before the encoding line. After encoding a coded line, the coded line is used as a reference line for the next coded line.

However, in order to prevent the spread of parts disturbed by transmission errors, after one line is one-dimensionally encoded, up to K-1 subsequent lines are two-dimensionally encoded.
The operation of inserting a one-dimensional encoded line again and continuing with a two-dimensional encoded line is performed. Here, K is called parameter K.

Furthermore, there are three encoding modes: vertical mode, pulse mode, and horizontal mode, and encoding procedures and the like for each mode are defined. Among these, the vertical mode is one in which the relative distance between the change point to be encoded on the encoding line and the corresponding change point on the reference line is within 0 to 3 pixels, and V _R if the change point is to the right of the change point on the reference line, V _L if it is to the left, and V _O if there is no displacement, or 1 to 3 depending on the relative displacement.
A total of seven types of encoding modes are defined.

The present invention was made by focusing on the fact that when an image changes continuously over each line, this vertical mode is well represented as having that change. In other words, the portion where the relative displacement from the corresponding change point on the reference line encoded immediately before the current encoded line is within the range of 1 to 3 pixels is defined as the density determination element of the image, and the calculation for this one line is The linear density is determined by comparing the numerical value with a certain reference value.

The present invention calculates the number of encodings in encoding modes V _L and _VR in a two-dimensional encoding line (L≠K when L = current encoding line and K = one-dimensional encoding line with parameter K). When counting and comparing this value with a certain reference value, if (reference value) ≦ (count value) then high resolution, if (reference value) > (count value) then standard resolution and sub-scanning line density are determined.

For example, as shown in FIG. 2, when the image has almost the same pattern across multiple scanning areas 12, such as a series of vertically continuous linear images on the screen 11 (in the two-dimensional encoding mode) (V _O mode, etc.) read signal 13 can be obtained, but the effect on image quality is extremely small whether the linear density is set to high resolution or standard resolution, so it is not enough to achieve high resolution.

In the case of the image pattern shown in Fig. 2, in the conventional line density switching control method shown in Fig. 1, each scanning line (i),
Since the number of change points detected in (ii), (iii), and (iv) is large, each line is regarded as a dense line, and a high-resolution line density is selected, reducing transmission efficiency. However, according to the present invention, a high-resolution line density is selected for the first line (i), but for lines (ii) to (iv) there is no relative change with (i), so the vertical mode V _O , so it can be ignored and the standard resolution line density selected. This will be explained in detail below.

FIG. 3 is a diagram for explaining the principle of the system of the present invention. In the figure, 14 indicates a screen, and 15 indicates a main scanning line. The pulse waveforms of the reference line and data line shown at the bottom of the figure represent black pixels of a character figure located above the corresponding position.
Data located below the pulses of the reference line (encoded) according to the encoding rules of CCITT Recommendation T.4
If the line pulse is shifted one pixel to the left
The vertical mode codes are given as V _L1 , V _L2 if the shift is two pixels to the left, and V _L3 if the shift is three pixels to the left. Similarly, in the case of rightward deviation, V _R1 ,
The vertical mode codes of V _R2 and V _R3 are given. If there is no pixel shift, the vertical mode code of V _O is given.

Since V _L and _VR indicate that the image is changing, they require higher resolution processing than V _O.
In this specific example, within one line as shown by to
Only V _L and _VR are counted and used as data for density determination.

Next, the present invention will be explained based on examples.

FIG. 4 is a block diagram showing the configuration of an example of a facsimile device implementing the method of the present invention. In the figure, reference numeral 16 denotes a transmission scanning section, which includes a photoelectric converter consisting of a photosensor array for converting an image into an electrical signal, a photosensor array driver, a pulse motor, and a pulse motor driver. Reference numeral 17 denotes a data compression unit, and 18 denotes a data decompression unit, which perform data compression and data decompression of image signals respectively according to the two-dimensional encoding method based on Recommendation T.4 as described above, and also perform data compression and data decompression of each image signal. The compression and data restoration processes incorporate a vertical mode code V _L /V _R encoding number counter and a density determination function for controlling linear density switching based on the method of the present invention.

Reference numeral 21 denotes a control unit, which has mechanisms for sequence control and line control for both transmission and reception. Reference numeral 22 denotes an interface section, which includes a modem and a network control device for connection with lines and telephones. Reference numeral 23 denotes a reception recording section, which is composed of a recording conversion section for electrostatic recording, a multi-stylus driver, a pulse motor, and a pulse mode driver.

The density determination signals from the data compression section 17 and the data restoration section 18 are used to control the pulse motor drivers in the transmission scanning section 16 and reception recording section 23, respectively. Sub-scanning line feeding is performed to provide density.

FIG. 5 is an operation flow diagram for the data compression section of this embodiment. The basic steps of this flow follow Recommendation T.4. When the process starts, it is first checked at 24 whether the scan line is the first one or the K line based on the parameter K. In the case of these lines, one-dimensional encoding processing is performed at 25. In the case of other lines, the process proceeds to step 26 and subsequent steps to undergo two-dimensional encoding processing based on the first line or K line.

The two-dimensional encoding processing after No. 26 is divided into path mode, vertical mode, and horizontal mode encoding processing according to the positional relationship of pixels between the reference line and the encoding line.

In step 26, it is checked whether the pixel corresponds to the pass mode (whether pixel b ₂ is to the left of pixel a ₁ according to Recommendation T.4). If applicable, pass mode encoding is performed at 27, and if not, it is further checked at 28 whether the vertical mode applies (whether the difference between pixel a ₁ and pixel b ₁ is 3 or less according to Recommendation T.4).

If the vertical mode is applicable, vertical mode encoding processing is performed at 29, and if not, horizontal mode encoding processing is performed at 30.

Every time vertical mode encoding processing is performed in 29, 31
The V _L /V _R mode encoding number counter is counted up by +1. The above processes are repeated while determining whether the end of the line is the end of the page at steps 32 and 33. Note that the V _L /V _R mode encoding number counter is
Although not shown, it is cleared at the end of the line.

At the end of each line scan, the content Pi of the V _L /V _R mode encoding number counter is checked at 34 and compared with the V _L /V _R mode encoding number reference value Q for density determination.
If Q≦Pi, an instruction signal to switch to high resolution linear density is generated at 35. If Q>Pi, the signal 35 generates a signal indicating the standard resolution linear density.

Note that the density determination for the one-dimensional encoded line (K line) is processed by substituting the coarseness determination result of the immediately preceding two-dimensional encoded line (K-1) line.

FIG. 6 shows an example of the line density in the sub-scanning direction processed in this embodiment. The meanings of the symbols in the diagram are as follows.

Pi: Number of V _L / V _R mode encodings for each line Q: Reference value of V _L / V _R mode encoding number for density determination Y: Line to be read/recorded at standard resolution Z: Line to be read/recorded at high resolution K: Parameter K in two-dimensional encoding method {m n}: Arbitrary natural number In the figure, line number n・K, (n+1)・
Every Kth line, denoted by K, (n+2)・K,..., is a line that is one-dimensionally encoded, and as mentioned above, density determination is not performed here, and the previous line, for example (n+1 )・K for (n
+1)・K−1 line density determination Q<Pi is applied. Therefore, (n + 1) K follows (n
+1)·K+1 line density is Z of the high resolution line. In general, Q=Pi or Q<Pi
The next line after the line for which the density judgment is obtained becomes Z, and the line whose number of density judgments is Q<Pi becomes Y of standard resolution.

As described above, the present invention scans at high resolution an encoded line in which the number of change points whose relative displacement with respect to the reference line is within 1 to 3 pixels is greater than the reference value, thereby detecting areas with many minute changes within one screen. By guaranteeing the image quality for the image and shortening the transmission time for parts with a large number of changes but few minute changes, it is possible to actually reduce the need for facsimile transmission, which is clearer and faster than the conventional method.

In addition, since a two-dimensional encoding compressor or decompressor is used, no other counter is required.
There are also great advantages in terms of circuit design, such as reducing the circuit scale and simplifying the device.

[Brief explanation of the drawing]

Figures 1a and b are explanatory diagrams of the conventional automatic line density switching control system, Figure 2 is an explanatory diagram of line density switching processing in a vertical line pattern, Figure 3 is an explanatory diagram of the principle of the present invention, and Figure 4 is an explanatory diagram of the line density switching process in a vertical line pattern. FIG. 5 is a block diagram of a facsimile apparatus according to an embodiment of the present invention, FIG. 5 is an operation flow diagram of the embodiment, and FIG. 6 is an explanatory diagram of processing results in the embodiment. In the figure, 16 is a transmission scanning section, 17 is a data compression section, 18 is a data decompression section, and 19 and 20 are V _L /V _R
Mode encoding number counter and density determination function, 2
Reference numeral 1 indicates a control section, 22 an interface section, and 23 a reception recording section.

Claims (1)

[Claims] 1 Compress or restore the image information using the two-dimensional encoding method, and the transmitting side changes the sub-scanning line feed according to the density of the image information of the encoded line and transmits it, and the receiving side changes the feed of the sub-scanning line according to the density of the image information received. In a facsimile device that restores the coded line by changing the sub-scanning line feed accordingly, when compressing or restoring the image signal, the vertical mode codes V _L and V _R regarding a certain coded line are counted, The counted value is compared with a predetermined reference value, and if the counted value is larger than the reference value, it is considered dense, and on the other hand, if the counted value is smaller than the reference value, it is considered coarse. An automatic line density switching control method characterized in that the density of an image is determined and the sub-scanning line density is sequentially switched in order to change the resolution based on the result of the determination.