JP2687417B2 - Automatic linear density switching system for facsimile machines - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear density switching system in a facsimile machine, and more particularly to an automatic linear density switching system in the sub-scanning direction.

Conventional Technology Conventionally, in this type of line density switching method in the sub-scanning direction,
The data change points of 0, 1 or 1, 0 of the binary image data of each line are counted in line units, and if the number of change points is equal to or more than an arbitrary constant, the next line image data is deleted and is equal to or less than an arbitrary constant. In that case, without deleting the next line image data,
The method of executing transmission was adopted.

Problems to be Solved by the Invention In the above-mentioned conventional method, the number of changes in image data for each line is detected. In other words, the autocorrelation coefficient in the image data time series for each line is calculated by calculating the adjacent image data. If this autocorrelation coefficient is greater than or equal to an arbitrary value, it is assumed that the entropy with the next line is high, and the next line is deleted and the transmission image data is compressed. Since the line density is controlled, accurate information compression cannot be performed because cross correlation between lines is not taken into consideration. For example, for a pattern having a high correlation in the sub-scanning direction and a low correlation in the main-scanning direction, the control is extremely useless. In addition, the thinned line is recorded by replacing the thinned line with the previous line without any special processing in the receiving facsimile machine, so the thinned line and the next line are connected. Has the disadvantage that it becomes worse.

The present invention has been made in view of the above-mentioned conventional circumstances, and therefore an object of the present invention is to provide a novel automatic linear density switching system capable of eliminating the above-mentioned drawbacks inherent in the conventional technology. Especially.

In order to achieve the above object, an automatic linear density switching method in a facsimile apparatus according to the present invention is an autocorrelation coefficient for each line of image data read and binarized by the facsimile apparatus. And the vertical adjacent image data with the previous line and the cross-correlation coefficient are also calculated, and line thinning in the sub-scanning direction is performed in consideration of entropy in the vertical and horizontal directions. With respect to the above, it is considered that the image quality that is visually good can be obtained by performing the interpolating smoothing processing predicted from the lines before and after the thinned line in the receiving side facsimile apparatus.

EXAMPLE Next, a typical example of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an automatic linear density switching system in a facsimile apparatus according to the present invention.

Referring to FIG. 1, the image data is processed by the image data A / D conversion and binarization unit 1, and in the sub-scanning line control unit 2, the correlation coefficient calculation unit and the sub-scanning line control signal generation unit 3 are processed.
The sub-scanning lines are thinned by the information from
The processed image data is MH or MR in the encoding unit 4.
It is encoded and sent from the modulator 5 to the line.

FIG. 2 is a system block configuration diagram of a correlation coefficient calculation and sub-scanning line density switching control unit.

In FIG. 2, input x _{i, j} represents binary image data. The x _{i, j} are input to the one-screen data delay element 6, and the calculation result is output from the autocorrelation coefficient generator 9.
In addition, the image data of one line before is accumulated in the working memory 7, the data processed by the cross-correlation coefficient calculation unit 8 is input to the cross-correlation coefficient generation unit 10, and the calculation result is output. .

Now, focusing on the i-th row and j-th column binary image data shown in FIG. 3, the concept of the autocorrelation coefficient H and the cross-correlation coefficient V will be shown.

Here, ι is the number of pixels for one line Calculation ab = + 1 (a = b) = -1 (a ≠ b) x _{i, j} are binary data of ± 1. The calculated correlation coefficients H and V are input to the sub-scan line control signal generator 11, and the control signal is passed to the sub-scan line controller 12 under the following conditions. Scan line decimation is performed.

Line thinning if H ≧ α and V ≧ β (3) No line thinning if H <α or V <β (4) However, α and β are arbitrary constants.

Further, in the receiving side facsimile apparatus, assuming that the i-th line in FIG. 3 is thinned and transmitted,
As shown by the above equations (3) and (4), it is assumed that the thinned lines have a high correlation with the surrounding image data, so that interpolation from the surrounding image data is easy. The following is assumed as an example of the interpolation of the i-th line.

xi, j = xi-1, j (when xi-1, j = x i + 1, j) or xi-1, j-1 (xi-1, j-1 = x i + 1, j + 1)
Or) xi-1, j + 1 (xi-1, j + 1 = x i + 1, j-1
(5) When the logical operation represented by the above equation (5) is executed in the facsimile machine on the receiving side, vertical lines and diagonal lines to the right and diagonal lines to the left are reinforced, and visually good image quality is obtained. To be

EFFECTS OF THE INVENTION As described above, according to the present invention, the transmission side of the facsimile apparatus executes the calculation of the autocorrelation coefficient and the cross-correlation coefficient for each line of the image data, judges the coefficient, and performs the sub-scanning. By having the automatic line density switching function for thinning lines, appropriate data compression is performed, and at the receiving side of the facsimile machine, by reproducing the thinned image data highly correlated with the adjacent image data by interpolation. , Visually good image quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an automatic linear density switching system according to the present invention, and FIG. 2 is a block diagram showing a concrete example of a correlation coefficient calculation unit and a sub-scanning line density switching control unit. FIG. 3 is a layout diagram of the read image data. 1 ... Image data A / D conversion and binarization unit, 2 ... Sub scanning line control unit, 3 ... Correlation coefficient calculation and sub scanning line control signal generation unit, 4 ... Encoding unit, 5 ... Modulator, 6 ... 1
Image data delay element, 7 ... Cross-correlation coefficient working memory, 8 ... Cross-correlation coefficient calculator, 9 ... Auto-correlation coefficient generator, 10 ... Cross-correlation coefficient generator, 11 ... Sub-scan Line control signal generator, 12 ... Sub scanning line controller

Claims (1)

(57) [Claims] 1. As a means for reducing transmission data and preventing image quality deterioration in a facsimile apparatus, for image data input from a reading unit, an autocorrelation coefficient is calculated for each line of the binary image data, and The image data for one line is accumulated, the cross-correlation coefficient with the current line is calculated, these two correlation coefficients are calculated in real time, and the value of the correlation coefficient is used as a condition to determine whether or not the current line can be transmitted. A facsimile machine including a function of automatically switching the line density in the sub-scanning direction and performing pixel interpolation smoothing processing on the thinned lines at the receiving side at the thinned line. Automatic linear density switching method in.