JPS635945B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image signal processing method for improving the recording reproducibility of facsimile image signals.

In a facsimile, a photoelectric conversion operation is performed on the original to be transmitted in the main scanning direction on the transmitter side.
The original is decomposed into pixel signals on each scanning line and then transmitted as serial image signals according to the scanning difference order, and the receiver side uses the received image signals to divide the scanning and the transmitter side. A recording scan is performed to record corresponding dot-shaped pixels, thereby obtaining a received image that is identical to the transmitted original.

However, when scanning is mainly performed on the transmitter side, it may be difficult to distinguish between black and white objects with high spatial frequency components, such as thin lines, due to photoelectric conversion processing.
When this is used as a received image, what should be a thin black line is often omitted, resulting in a so-called missed reading phenomenon. In order to solve these drawbacks, a means is provided for determining the halftone signal between the white signal and the black signal, and by this means, the halftone signal after the white signal is forced to be the black signal,
Furthermore, there is a system in which the halftone signal after the black signal is forcibly determined as a white signal and the image signal is sent out. However, although this method can prevent the above-mentioned phenomenon of missing thin lines in the sub-scanning direction, since the halftone signal is forcibly determined as a black or white signal and sent, the halftone signal is continuous for a long time. If the line is thin in the main scanning direction, it has the disadvantage that it is easy to miss.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image signal processing method for preventing the main/sub-scanning omission phenomenon on a received image and improving the resolution of the portions of a transmitted image that change from black to white and from white to black. It is about providing.

In order to achieve such an object, the image signal processing method according to the present invention processes a white signal exceeding a first discrimination level, a black signal below a second discrimination level, and a first discrimination level and a second discrimination level for a facsimile image signal. means for sequentially extracting signals corresponding to three gradations of a halftone signal between the image signals from the image signal; and a means for sequentially extracting signals corresponding to three gradations of the intermediate tone signal from the means, and determining whether the signal corresponding to the three gradations extracted from the means is a black signal as the immediately preceding image signal. , or storage means for storing whether the signal is a white signal or a halftone signal, and a storage means for storing whether the image signal is a white signal or a halftone signal; means for transmitting a white signal and transmitting a black signal in place of the halftone signal when the immediately preceding image signal is a white signal and a halftone signal; a signal in place of the halftone signal and the white signal and the black signal; The present invention is composed of means for combining and transmitting the images at the same timing, thereby preventing the phenomenon of missing thin lines on the received image, and improving the resolution of the portions of the transmitted image that change from black to white and from white to black. This is what I did.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the image signal processing method according to the present invention, in which the halftone output after the black signal output is used as the white signal in a configuration in which up to one pixel signal of the halftone output is used. It is. In the same figure,
a peak value hold circuit PH that holds the highest value in the white level direction of the image signal given from the input terminal In;
Based on the peak value output of this peak value hold circuit PH, a potentiometer RV ₁ sets the discrimination level L ₁ of the white level W, and a discrimination level L ₂ of the intermediate level between the white level W and the black level B is set. Potentiometer V ₂ and these discrimination levels
Comparators CM 1 and CM each have L ₁ and L ₂ as one input, and input the image signal given from the input terminal In to the other, and send out the output when the input level of the image signal exceeds the _respective discrimination level. ₂ and these comparators
They are set by the outputs of CM ₁ and CM ₂ , respectively, and reset by the reset clock pulse CPr.
RS flip-flops FF ₁ and FF ₂ and these
D-type flip-flops FF 3 and _{FF 4 receive} the outputs of the RS flip-flops FF ₁ and FF ₂ , respectively, and sample and hold them using the sample clock pulse CPs given at a predetermined timing;
D to send out the output of flip-flop _FF4 , that is, the halftone output, for one pixel as a white signal.
Type flip-flop FF ₅ and AND gate AG ₁
and an OR gate _OG1 which synthesizes the white signal for one pixel sent from the AND gate AG1 and the white signal obtained from the output of _the D-type flip-flop _FF3 and outputs the result. The reset clock pulse CPr and the sample clock pulse CPs are provided as shown in FIGS. 2a and 2b. Also, at the input terminal In,
As shown in Fig. 2c, a picture signal, that is, a pixel signal, synchronized with the clock pulse CPr is provided.
The upper reference line is the black level B, and the lower line is the lower level W.

In addition, the peak value hold circuit PH, potentiometers VR ₁ , VR ₂ , comparators CM ₁ , CM ₂ , RS flip-flops FF ₁ , FF ₂ , and D-type flip-flops
FF ₃ and FF ₄ constitute means for sequentially extracting signals corresponding to three gradations from the facsimile image signal. That is, when there is an output from the D-type flip-flop FF ₃ , it is an unconditional white signal, and when there is no output from both the D-type flip-flops FF ₃ and FF ₄ , it is a black signal, and only the output from the D-type flip-flop FF ₄ is present. is a halftone signal.

The operation will be explained in detail below using the time chart shown in FIG.

First, when the image signal shown in FIG. 2c is applied to the input terminal In, _the comparators CM ₁ and _CM
Outputs as shown in Fig. 2d and e are sent from CM ₂ . The output of the comparator _CM1 is generated only when the image signal exceeds the discrimination level _L1 , and the output of the comparator _CM2 is generated only when the image signal exceeds the discrimination level _L2 .
Therefore, when the outputs of comparators CM ₁ and CM ₂ are generated, a white signal is generated, when both comparators CM ₁ and CM ₂ are not generating outputs, a black signal is generated, and only the output of comparator CM ₂ is generated. When it is, it is judged as a halftone signal. Although no particular output is produced as a black signal, the time when the output of the comparator _CM2 is not produced can be considered as a black signal.

The image signals whose density levels have been determined by these comparators CM ₁ and CM ₂ are set to RS flip-flops FF ₁ and FF ₂ as white signals and halftone signals, respectively. To explain the order of the image signals shown in the time chart of FIG. 2, first, the image signal is determined to be a white signal, and RS flip-flops FF ₁ and FF ₂ are set at the same time. The set state of these RS flip-flops FF ₁ and FF ₂ continues until they are reset by the next clock pulse CPr, as shown in FIGS. 2f and 2g, respectively. The outputs of these RS flip-flops FF ₁ and FF ₂ are sampled and held in D-type flip-flops FF ₃ and FF ₄ , respectively, by the rising edge of the sampling clock pulse CPs that rises after time tD from the rising edge of the clock pulse CPr. Then, signals corresponding to the three gradations of white, black, and intermediate tones are sequentially extracted from the image signal. Figures 2h and 2i show the outputs of the D-type flip-flops _FF3 and _FF4 . On the other hand, the D-type flip-flop FF ₅ is also triggered by the clock pulse CPs at this time, and the output of FF ₄ is temporarily stored as _the previous image signal. is not set, this D-type flip-flop _FF5 is not set. In other words, the image signal before the image signal in FIG. 2c was a black signal. Therefore, the AND gate _AG1 sends out a white signal for one pixel as shown in FIG. 2k in accordance with the memory contents of the D-type flip-flop _FF5 . And the white signal output of this AND gate AG ₁ is OR gate OG ₁
The image signal output to the output terminal Out is combined with the output of the D-type flip-flop FF ₃ , but since the white signal is also output from the D-type flip-flop FF ₃ at this time, the image signal output to the output terminal Out is combined with the output of the D-type flip-flop FF 3. The corresponding white light will be activated. The image signal obtained at the output terminal Out is a white signal at the "H" level, and is output after a time tD after the image signal is applied to the input terminal In (FIG. 2, 1). Next, when an image signal is applied, since the signal level is less than the discrimination level _L2 , it is determined as a black signal. Therefore,
Both RS flip-flops FF ₁ and FF ₂ are not set, and D-type flip-flops FF ₃ and FF 2 are not set.
FF ₄ is also reset by the clock pulse CPs after a time tD after the image signal is applied. on the other hand,
Since the D-type flip-flop _FF4 had been set by the image signal, the D-type flip-flop _FF5 is set by the clock pulse CPs at this time. In other words, the D-type flip-flop _FF5 is
This means that the output of the D-type flip-flop _FF4 is read after one cycle of the clock pulse CPs.
The fact that the D-type flip-flop _FF5 is set means that a white signal was input one period before the clock pulse CPs. In this way, once the D-type flip-flop _FF5 is set, if the next image signal is a halftone signal, the D-type flip-flop _FF5 is reset by the rising edge of the clock pulse CPs, and only the D-type flip-flop _FF4 is reset. is set, the halftone signal at this time is 1
A white signal corresponding to the number of pixels is sent out from AND gate _AG1 . That is, when the image signal read into the image signal is a halftone signal as shown in FIG. 2c, only the D-type flip-flop _FF4 is set. Then, since the D-type flip-flop _FF5 has already been reset by the image signal, the AND gate
The input condition of AG ₁ is met and a white signal is sent from its output. In this way, the AND gate _AG1 , which sends out a white signal as a substitute for the extracted halftone signal, causes the D-type flip-flop _FF5 to update the output content of the D-type flip-flop _FF4 with a delay of one cycle of the clock pulse CPs. Therefore, the input condition of AND gate AG ₁ is clock pulse CPs.
holds true for only one period. That is, in this embodiment, the white signal as a substitute for the halftone signal following the black signal is always sent for one pixel. All subsequent halftone signals are processed as black signals.

Therefore, in the photoelectric conversion process of thin lines, etc. when scanning documents on the transmitter side, even if an image signal is input at a level that is difficult to distinguish between black and white, it will not be processed as a white signal or a black signal, but will be converted into a black signal. Since the subsequent halftone signal is treated as a white signal for one pixel and the rest as a black signal, it is possible to prevent the thin line dropout phenomenon and improve the resolution of the transition part from black to white and from white to black in the transmitted image. can be done.

Further, this embodiment has similar effects when applied not only to the transmitter side but also to the input side of the receiver.

As explained above, according to the present invention, it is possible to completely prevent the phenomenon of missing fine lines in both the main and sub-scanning directions on a received image in a facsimile device, and at the same time, it is possible to completely prevent the phenomenon of missing thin lines in both the main and sub-scanning directions on a received image in a facsimile device, and at the same time, it is possible to completely prevent the phenomenon of missing thin lines in both the main and sub-scanning directions on a received image, and at the same time, it is possible to completely prevent the phenomenon of missing thin lines in both the main and sub-scanning directions on a received image in a facsimile device. Since the resolution can be improved, it can be used to reproduce fine lines in black-and-white two-tone drawings, etc., and has an extremely excellent effect.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the image signal transmission system according to the present invention, and FIG. 2 is a time chart for explaining the operation of the circuit shown in FIG. PH...Peak value hold circuit, CM ₁ , CM ₂ ...
... Comparator, RV ₁ , RV ₂ ... Potentiometer,
FF ₁ , FF ₂ ...RS flip-flop, FF ₃ , FF ₄ ,
FF ₅ ...D flip-flop, AG ₁ ...AND gate, OG ₁ ...OR gate.

Claims (1)

[Claims] 1. First and second discrimination levels are provided for a facsimile image signal, and a white signal exceeding the first discrimination level, a black signal below the second discrimination level, and a difference between the first discrimination level and the second discrimination level are provided. means for sequentially extracting signals corresponding to three gradations of intermediate tone signals from the image signal; and a signal corresponding to the three gradations extracted from the means as the immediately preceding image signal, which is a black signal, or storage means for storing whether the signal is a white signal or a halftone signal, and a white signal is output in place of the halftone signal when the immediately preceding image signal is a black signal according to the storage contents of the storage means for each halftone signal taken out; means for transmitting a black signal in place of the halftone signal when the immediately preceding image signal is a white signal and a halftone signal, and a means for transmitting a black signal in place of the halftone signal; An image signal processing method characterized by comprising: a means for combining and transmitting the synthesized signal at the timing of .